Feeling of being bumped when stopped [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Feeling of being bumped when stopped


March
04-08-2006, 02:18 AM
has anyone ever experience the feeling of being bumped from behind only to look in your review mirror and no one hit you? occasionally when at a stop sign/light i get a jolt like someone bumped my vehicle from behind which of course didn't happen ...any ideas why??/


Lisa

ugotmale2day
04-08-2006, 02:23 AM
Is this coming from a woman? Iam thinking it is? hehe

March
04-08-2006, 02:46 AM
lol....yessssssssss, and i just realized I posted on the trailBlazer instead of the Envoy to make matters worse. But I am serious about the question it really does happen.:(

ENVOY2LOW43
04-08-2006, 02:49 AM
has anyone ever experience the feeling of being bumped from behind only to look in your review mirror and no one hit you? occasionally when at a stop sign/light i get a jolt like someone bumped my vehicle from behind which of course didn't happen ...any ideas why??/
Actually it did happen to me i think twice. My wife thought somebody hit us from behind. It happened right after stopping about a second later. It's kinda strange and I have no idea what must have caused it.:confused:

Gaspar
04-08-2006, 03:02 AM
Yes, everytime I stop a little hard I feel that small bump right after the TB stops. Maybe something with the breaks? (I hope not)

-Gaspar

March
04-08-2006, 03:12 AM
i just had the envoy in because of 4w drive problems and they replaced the transfer switch. When I picked it up the cashier asked if they took care of the bump.....I assumed they did so she asked the service guy and he said with a confused face "oh ya that was related to the 4w drive problem" I really think he forgot to look at it and was passing if off as part of the problem with the switch. The bump happen again tonight so they didn't fix it.

Lisa

ps thats what the hubby said maybe the breaks.

Dave
04-08-2006, 04:53 AM
Moved to the correct forum.

MTPockets
04-08-2006, 07:28 AM
I havent been under my 2005 TB much yet, but a driveline thump or bump upon a stop or take-off on a 4x4/AWD is usually a dry slip yoke on the font or rear driveshaft. The driveshafts need to 'telescope' in/out to absorb chassis/drivetrain movement. A nice layer of (thick/sticky) grease in the 'telescoping' slip yoke is needed. If it drys up, the movement becomes abrubt and jerky, giving the *bump* feeling. Not sure if the envoy has grease fittings or not on the driveshafts (look for rubber boots on the driveshafts), but most require the driveshafts to be dropped, boot clamps cut, driveshaft serperated, splines cleaned, regreased and the hole thing reassembled and reinstalled with new boot clamps. The driveshafts are typically flanged & bolted at both ends for easy removal. You also need to mark the driveshaft halves anytime you seperate it @ the splines so you reassemble it the same way for proper balancing. Slip yokes are one of those 4x4 maintenance items that never seem to get listed anywhere.:duh:

G/luck
Joel

rbarrios
04-08-2006, 01:30 PM
Ive also experienced a small bump- under 2 scanarios...
1- I have slowed down suddenly and right before I stop completely, i feel a light bump/jerk, and I attribute that to the driveshaft/gears "letting go" is the best I can describe it... or shifting into the lowest gear........
Ive felt it in my 70 Monte carlo too... so thats what I think my case is....
the other case is when im on a road or highway and my side of the road or lane has come to a stop and the opposite side of the road has vehicles traveling at fast speeds... as a vehicle drives by it creates a wave of air or a small vacuum and I can feel the trailblazer move... sometimes its enough movement that I think the vehicle behind me has tapped my bumper.. and I look and the car is at a safe distance behind me.
Semis will cause this if im slowly moving. trucks, suvs cause it more, and some passenger cars will do it also if theyre traveling fast enough in the opposite lane....
But i feel this alsmost everyday when im stuck in traffic in Loas Angeles in morning rush hour and im in the carpool lane and the oopsite side of the freeway has a car zoom by at 75 mph... , i can feel the TB really move.

betts687
04-09-2006, 03:43 AM
i had the same prob. and every few times it did it the oil pressure gage would drop and the driver info display said oil pressure low. apparently my truck was leaking oil, and enough to make a noticable difference. moreover, when you come to a stop, the pressure drops (which is normal), but if your low on oil, the pressure gets too low, and the engine begins to stall. mine died on me several times after this happend. pay attention to if your truck is leaking oil. at first the dealer couldn't find a problem, then i noticed it leaking oil and took it in for that, and they had to put die in my oil to find my leak. once the leak was fixed, no more problems since

Dshow
04-10-2006, 01:49 PM
I have experience this when starting from a stop. The first time it happened I almost got out to see if there was any damage... I think this has to do with the rear brakes releasing. They appear to let go after the front and it gives you the bumping sensation.

Envoy Fan
04-10-2006, 01:56 PM
has anyone ever experience the feeling of being bumped from behind only to look in your review mirror and no one hit you? occasionally when at a stop sign/light i get a jolt like someone bumped my vehicle from behind which of course didn't happen ...any ideas why??/


Lisa

Do you by any chance have the rear air suspension on your Envoy?

MTPockets
04-10-2006, 08:18 PM
So much for the dry driveshaft slip-yolk idea (that was the cause on isuzu rodeos & my old chevy truck). It looks like TB's dont even have them.:duh: I got a good look underneath my 2005 LS 4x4 to notice this. The only unfamiliar thing I noticed was a funky flex coupling type thing at the transfer case end of the front driveshaft? :confused: Never saw anything like it. Instead of a slip-yolk and u-joint at that end, there's only cylinder/barrel shaped coupling thingy on the xfer case end?! What the heck do u call them?

Thanks
Joel

the roadie
04-10-2006, 09:01 PM
The only unfamiliar thing I noticed was a funky flex coupling type thing at the transfer case end of the front driveshaft?

CV (Constant Velocity) joint. Less rotationally erratic than U-joints.

http://www.roadie.org/FrontSuspension.JPG

MTPockets
04-10-2006, 09:18 PM
CV (Constant Velocity) joint. Less rotationally erratic than U-joints.

Cool pic! :hail: The joint I'm referring to is at the transfer case output, on the drivshaft that goes to the front diff. It's got a metallic collar on it. Also wassup with the ball joints? They look like they are integral with that cast steering knuckle?

Joel

the roadie
04-11-2006, 01:34 AM
Cool pic! :hail: The joint I'm referring to is at the transfer case output, on the drivshaft that goes to the front diff. It's got a metallic collar on it. Also wassup with the ball joints? They look like they are integral with that cast steering knuckle?

Sorry.:o I should have figured you knew what front driveshaft CV joints were. The manual calls the shaft from the transfer case to the front differential a prop shaft.

Anyway, that's an excellent question. The shop manual, page 4-5 calls out the front u-joint spider assembly and the shaft itself, but is silent on the function of the collared item. No cross section or replacable parts shown.

On page 4-17, the theory of operation says the front prop shaft consists of a shaft tube, u-joint, flange yoke, and a CV joint. So I'd guess the mystery collar is hiding a CV joint. Why, I don't know.

The manual has a LOT more details about how the CV joints in the front drive shafts can be rebuilt, with many drawings. But the front prop shaft is not documented 1/10 as well.

Oh, and the ball joints? The upper control arm has what they call a pinch bolt and nut that clamps the top end of the upper ball joint. Once you remove the pinch bolt, you can pry the upper control arm up off the cast steering knuckle. The ball joint is retained by a circlip that's normally hidden since it's between the control arm and the steering knuckle. Once the circlip is off, you can press out the ball joint.

The lower ball joint is retained by a flared flange! You have to chisel off the old one before you press out the old joint, and the installation instructions refer to a special GM flare tool. The designers of this suspension were especially evil.

MTPockets
04-11-2006, 09:33 AM
Great info roadie. Thanks. That does make sense that the item on the front prop shaft is a type of CV joint as something has got to have some 'give' in this system (move axially). The rear prop shaft appears solid (not allowed to move axially) which seems very odd for a 4x4. Man... I would never have figured out the circlip/flange thing for the upper/lower BJ's!! I thought the 3 rivet deal on the older GM's was very rude of the suspension designers.:hissy:

Joel

the roadie
04-11-2006, 09:57 AM
The rear prop shaft appears solid (not allowed to move axially) which seems very odd for a 4x4.

The shaft is solid, but there is a traditional slip spline section where it connects to the transfer case. The transfer case rear output has a longish "snout" to accommodate the slip spline, and the seal is at the rearmost part of the snout, so you can pry it out with a screwdriver when the prop shaft is removed.

The front prop shaft out of the transfer case doesn't need a dynamic slip spline because the geometry is fixed. The transfer case is hard bolted to the rear of the transmission, and the front differential is bolted to the oil pan, so there's no relative motion for the shaft to accommodate.

If somebody ever does a SAS (solid axle swap), the front prop shaft would have to have some slip spline section and much more serious joints. Maybe in 5-6 years when my daily driver might be a full electric vehicle, I can take the Envoy down for a few months and put in a pair of Dana 60's. :rotfl:

CopyGuard
04-11-2006, 11:16 AM
Both my 96 and 2000 Tahoes did the same thing here in Florida. When they got real dry. it would clunk almost every time you took off from a stop. Sitting in traffic after a hard stop the thing would let go with a bump and a clunk.
Grease'er up and that will go away.

Envoy Fan
04-11-2006, 11:42 AM
Both my 96 and 2000 Tahoes did the same thing here in Florida. When they got real dry. it would clunk almost every time you took off from a stop. Sitting in traffic after a hard stop the thing would let go with a bump and a clunk.
Grease'er up and that will go away.

Your bump different than thread starter. Origional poster stated felt a bump while sitting still.

MTPockets
04-11-2006, 03:16 PM
You usually get the *thump* somewhere between the time of releasing the brake pedal and hitting the gas pedal, so you could essentially be not in motion yet. That's how the 'slip-yolk thump' worked anyway. My bets are still on some type of driveline bind induced movement causing this.

G/luck
Joel

Matt
04-11-2006, 03:43 PM
I have the exact same problem as the original poster. The "bump" actually does occur while at a dead stand still, constant brake pressure applied. It seems to only occur when coming to a full stop shortly after the truck has just been sitting (Like when I stop at the very first stop light after I leave work and the Envoy as sat all day). Also, someone asked if the original poster had the air suspension...I do. I haven't really thought too much about it, but will inquire to the dealer next time I'm in for an oil change.

Envoy Fan
04-11-2006, 03:48 PM
Matt, welcome to the forum:yes:

Your post describes exactly what was happening to me when I had my '03 Envoy SLT with air suspension. After startup, and then come to a complete stop and about 20 seconds later (while foot on brake pedal and selector in drive) the mysterious bump would occur. Usually only once, but on occasion two or three times while still at the origional stop. Service dept never able to fix. Ended up trading and no problems yet on my '05 Envoy, also with air suspension.

Matt
04-11-2006, 04:46 PM
Envoy Fan,

Thanks for the welcome. What happened with your 03 is exactly what is happening with my 05 Denali. It is just more of an annoyance than anything and doesn't occur on a daily basis. I certainly won't plan a special trip to the dealership for it, but just might mention it next time I'm in for service. Who knows?!

Matt, welcome to the forum:yes:

Your post describes exactly what was happening to me when I had my '03 Envoy SLT with air suspension. After startup, and then come to a complete stop and about 20 seconds later (while foot on brake pedal and selector in drive) the mysterious bump would occur. Usually only once, but on occasion two or three times while still at the origional stop. Service dept never able to fix. Ended up trading and no problems yet on my '05 Envoy, also with air suspension.

Envoy Fan
04-11-2006, 04:52 PM
Envoy Fan,
Thanks for the welcome. What happened with your 03 is exactly what is happening with my 05 Denali. It is just more of an annoyance than anything and doesn't occur on a daily basis. I certainly won't plan a special trip to the dealership for it, but just might mention it next time I'm in for service. Who knows?!

:duh: Didn't realize you had a Denali. At what mileage did yours start to do this?

CopyGuard
04-11-2006, 11:03 PM
Envoy Fan,
As I said, the bump happened while sitting still after a fairly hard stop. The yolk gets hung up and then breaks lose while sitting at a light. The first time it happened, I looked in the mirror expecting to see knuckles on a steering wheel behind me, yet noone was around but me.
The other thing I mentioned, the clunk, happens only when accelerating.
Took it into the dealer and they greased the yoke. Stays for about six months. Then starts up again.

thebeast
04-11-2006, 11:54 PM
I'm with Joel on this one. I think it has something to do with the driveline. My Ascender does it. Just like Joel, I thought it was the same thing my other Isuzus did. You always had to grease the yoke. I would bet the thump won't hurt anything, but it would be nice to fix it.
jeff

Matt
04-12-2006, 09:16 AM
:duh: Didn't realize you had a Denali. At what mileage did yours start to do this?

No problem, I don't think I said anything previously to indicate that. I think it started around 7,500 miles or so. I'm currently at about 16,000. Now that I think about it, the weather is starting to really get warm here, 70's, and it hasn't done it for a while.

my-tb
04-12-2006, 03:47 PM
I am getting the same deal with mine on acceration and braking. I have an 04 W/ 22k 2wd and G80. So does the slip yolk thing still apply to mine? Lord knows I have thought several times I was tapped and when giving it gas it seems like the drive shaft might break off. One more thing to take it in for.

March
04-16-2006, 12:24 AM
Do you by any chance have the rear air suspension on your Envoy?

Yes I have rear air suspension!

Lisa

March
04-16-2006, 12:28 AM
Your bump different than thread starter. Origional poster stated felt a bump while sitting still.

Yes your right my bump is differnt, the bump only occurs when stopped and the brakes firmly applied. Doesn't happen everytime you stop.:worried:

Lisa

March
04-19-2006, 11:35 AM
:duh: I needed to vent........well the envoy is in service as we speak. This is the third time and each time I have explained in detail how is bumps only when at a COMPLETE stop. They service guy calls and says its normal for the bump to happen when driving out of a stop its the shifting:duh: ....Hello!! I explained for the third time only when I am stopped COMPLETELY not while moving and anywhere from 5 to 20 seconds later a bump and my foot it on the brake!! The guy says that is different...YA ... looks like a huge communication problem.
When you call the service you speak to a lady who writes down the problem, when I drop it off the vehicle no one in service asks you to explain the problem. But I explained it once again in detail to the service guy and he still gets it wrong:duh: . I think he may get it now because I explained for a fourth time ....hopefully. thanks for letting me vent...not that you wanted to here it but at least I feel better:)

Jr_454
04-21-2006, 01:17 PM
Hey everyone I have a 05 TB and just brought it in to the dealer ship to havet he brakes looked at. If felt like the peddle was dropping just before a complete stop. The mechanic said that they have had to replace the rear calipers on some of the full size trucks for the same reason pedal drop or a pedal that go's almost the floor. I will let every one know if this is the problem but it sounds like this may be the problem.

Envoy Fan
04-21-2006, 04:01 PM
:duh: I needed to vent........well the envoy is in service as we speak. This is the third time and each time I have explained in detail how is bumps only when at a COMPLETE stop. They service guy calls and says its normal for the bump to happen when driving out of a stop its the shifting:duh: ....Hello!! I explained for the third time only when I am stopped COMPLETELY not while moving and anywhere from 5 to 20 seconds later a bump and my foot it on the brake!! The guy says that is different...YA ... looks like a huge communication problem.
When you call the service you speak to a lady who writes down the problem, when I drop it off the vehicle no one in service asks you to explain the problem. But I explained it once again in detail to the service guy and he still gets it wrong:duh: . I think he may get it now because I explained for a fourth time ....hopefully. thanks for letting me vent...not that you wanted to here it but at least I feel better:)

Seems to be a common problem in the service dept. If you don't speak directly to the technician problems often occur. Hope that they can duplicate your problem and come up with a fix. It is not "normal". Keep us posted.

Dave
08-30-2006, 08:35 PM
Has anyone found the fix for this issue (feeling like you are bumped while you are stopped)? My Denali is doing it right now. It feels like it comes through the brake pedal. My natural instinct is to push the pedal harder. It happens through out the day but not every time. I'm going to have the dealer look at it during its next service. The problem really doesn't bother me. It can be annoying but not near as bad as the radio noise on my first Denali.

Jr_454
08-31-2006, 10:16 AM
Just had the TB in again and they repalaced the Master Cyl and said that it had an internal leak. Will see if this fixes it. the tech also said that the bumb is sometimes from the transmission disengaging i am not sure if this is true or not, I still feel it a little bit but it has gotten better and this happens just before a dead stop.

big ed
08-31-2006, 01:48 PM
my voy was this problem too. but it seems some people are mixing 2 different things together. when stopped it seems like your brakes have let go, but you don't move or your first thought is you got bumped. it only happens sometimes, I'll have to see if its after the first start of the day.I don't think its anything serious and don't think its worth having checked out or dealing with stealership

Envoy Fan
08-31-2006, 01:55 PM
I'm thinking all the owners that are having the "bump" while stopped have the air suspension.:undecided

big ed
08-31-2006, 02:01 PM
I'm thinking all the owners that are having the "bump" while stopped have the air suspension.:undecided

yes I do, is that the cause?

OurZoo
08-31-2006, 02:06 PM
No, I get this sensation from time to time and I don't have the air suspension. Only happens when I'm running the AC. I always look behind me too and I always wonder if it was my fault and somehow my foot wasn't completely on the brakes.

Envoy Fan
08-31-2006, 02:09 PM
yes I do, is that the cause?

Seems to be a common denominator in the "bump". The problem has been discussed over on Edmunds. A Rainier owner reported that he got it fixed with a new driveshaft. Haven't heard him saying if problem solved or not. An Envoy owner over there asked his dealer for same fix, was denied because it was a Rainier that was repaired, not an Envoy.

big ed
08-31-2006, 02:19 PM
Seems to be a common denominator in the "bump". The problem has been discussed over on Edmunds. A Rainier owner reported that he got it fixed with a new driveshaft. Haven't heard him saying if problem solved or not. An Envoy owner over there asked his dealer for same fix, was denied because it was a Rainier that was repaired, not an Envoy.

thanks for the info. I'm not worried about it, more of a annoyance than a problem.

Envoy Fan
08-31-2006, 03:12 PM
Has anyone found the fix for this issue (feeling like you are bumped while you are stopped)? My Denali is doing it right now. It feels like it comes through the brake pedal. My natural instinct is to push the pedal harder. It happens through out the day but not every time. I'm going to have the dealer look at it during its next service. The problem really doesn't bother me. It can be annoying but not near as bad as the radio noise on my first Denali.

How many miles on your Denali before you noticed the "bump"?

gbman209
09-01-2006, 08:17 PM
Have the same problem with my 06 TB EXT 2WD 4.2. Happens ony after starting cold and coming to a stop before eng reaches full op temp bumps 1-3 times but not every time under these conditions. Feels like a misfiring cyl but no check eng light yet

Dave
09-18-2006, 01:17 AM
I'm thinking all the owners that are having the "bump" while stopped have the air suspension.:undecided


I think Envoy Fan might be right about the bump that occurs when you are 100% stopped. Your tranny gears and drive shaft are not rotating. The main question is does it happen to everyone with the air suspension and why does it take thousands of miles to be noticed. It should happen when the vehicle is brand new. I will listen for the air suspension noise next time it happens.

jjl1298
09-18-2006, 02:45 AM
I have the same problem on my 06 TB LS with 18,000mi on it. Only when its cold. It almost feels like its coming from the rear like a caliper is releasing late or something. But the same "bump" feeling as you guys described. i never thought about the driveshaft.

dufunnel
09-19-2006, 10:06 AM
I haven't really noticed it in my 06 Denali, but I have this really bad in my 01 F150 Supercrew 2wd. It sounds to me like it's in the driveline there, but since my Denali is so much quieter I don't even notice it there, if it even happens. Maybe I'll keep my eye out to see if I get it there. I've got 15000 miles on the Denali.

AllThings_SS
09-19-2006, 10:57 AM
It has not happen to me but it does remind me of a funny story... When my wife first started driving she bumped this guy, not hard but enough to notice, So he turns around and my wife was looking straight ahead like nothing happened, So you can she the puzzled look on the guys face :duh: like did she bump me??? or was it my imagination. So he turns back around and keep driving. We still laugh at that one :rotfl:

anglarry04
10-29-2006, 10:41 AM
hope this thread isnt dead yet, but I was gonna post one on this too. I have the same issue. Mine is an 06 tb with 17,000, 2 wheel drive, 6cyl. The first clunk I noticed as I got in about to drive off. I did let the truck idle maybe a min to get situated. As I shifted gears, I got that bump, so I figured it was the trans engaging. However yesterday, it happened to me twice. Both times I was just sitting in a parking spot ac on and idling, not on the brakes. All I can figure is maybe the suspension settling, or since I have the park brake on, the caliper settles with the weight of everyone in the truck, or maybe the ac compressor cycling on, but thats one huge jolt if it is. I don't know if I have that air suspension you guys are talking about. Any takers?

bobzilla
10-30-2006, 03:27 PM
I too have noticed it in my 02 TB. Sitting at a complete stop and I could have sworn I got tapped, but no one was behind me.

diggitydog
11-02-2006, 07:18 PM
I have an 04 Rainier I6 AWD with air suspension. This "bump" occurs to me quite frequently (3 to 4 times a week), but only on the first long stop after the truck is parked for awhile. I also have to be stopped for at least 15 or 20 seconds before it occurs.

At first, I too thought I was rear-ended. I even reached for the glove box to get my insurance card while looking in the rear view, only to see nobody behind me. Now, I've come to expect it, and press the brake pedal extra hard at long stop lights in anticipation.

Sometimes, I get 2 or 3 smaller bumps in a row, but mostly it is one larger surge.

I just got it back from picking up the Rainier at the dealer who was checking this out among other things, and of course they "could not duplicate the problem." Funny thing is, as I drove off somewhat disappointed in their futile attempt, I looped around the parking lot and stopped in a secluded area .... began counting to 20 ... and "BUMP".

Don't know how hard to press this, but it is rather annoying. My warranty runs out next summer so I want to get it resolved by then. If anybody has any info regarding a fix please do share.

Thanks,
Dave - Minneapolis

Super 88
11-02-2006, 08:40 PM
I just got it back from picking up the Rainier at the dealer who was checking this out among other things, and of course they "could not duplicate the problem." Funny thing is, as I drove off somewhat disappointed in their futile attempt, I looped around the parking lot and stopped in a secluded area .... began counting to 20 ... and "BUMP".

Thanks,
Dave - Minneapolis

I don't have any info of fixing the problem, but if it was me I would have went back into the dealership and asked the service manager to jump in the vehicle with you and go back to the parking lot and show him what you found!

Of course he might respond with "Oh, they all do THAT"!:crazy:

the roadie
11-02-2006, 09:16 PM
Of course he might respond with "Oh, they all do THAT"!:crazy:Being able to say that lie with a straight face is a job requirement. They all take training on lying convincingly. :mad:

Blueblazed
11-03-2006, 02:42 AM
Being able to say that lie with a straight face is a job requirement. They all take training on lying convincingly. :mad:

True! Very sad, but true! I wish I had a dollar for everytime I've heard that! :yes:

diggitydog
11-03-2006, 11:20 AM
I don't have any info of fixing the problem, but if it was me I would have went back into the dealership and asked the service manager to jump in the vehicle with you and go back to the parking lot and show him what you found!

Of course he might respond with "Oh, they all do THAT"!:crazy:

Thanks Super 88, problem is it only happens once. After that, it won't happen until it sits for a long time and is restarted cold.

Makes it quite difficult to reproduce for them. I'll have to be more persistent.

Envoy Fan
11-03-2006, 12:25 PM
I have an 04 Rainier I6 AWD with air suspension. This "bump" occurs to me quite frequently (3 to 4 times a week), but only on the first long stop after the truck is parked for awhile. I also have to be stopped for at least 15 or 20 seconds before it occurs.

At first, I too thought I was rear-ended. I even reached for the glove box to get my insurance card while looking in the rear view, only to see nobody behind me. Now, I've come to expect it, and press the brake pedal extra hard at long stop lights in anticipation.

Sometimes, I get 2 or 3 smaller bumps in a row, but mostly it is one larger surge.

I just got it back from picking up the Rainier at the dealer who was checking this out among other things, and of course they "could not duplicate the problem." Funny thing is, as I drove off somewhat disappointed in their futile attempt, I looped around the parking lot and stopped in a secluded area .... began counting to 20 ... and "BUMP".

Don't know how hard to press this, but it is rather annoying. My warranty runs out next summer so I want to get it resolved by then. If anybody has any info regarding a fix please do share.

Thanks,
Dave - Minneapolis


What you have related is EXACTLY what I was experiencing when I had my 2003 Envoy SLT with the air suspension. Is it related to the air suspension or something in the drive train? I don't know, but the sensation was coming from the rear of the truck. Problem for me went away when I sold it and got my 2005 Envoy Denali. It hasn't developed the problem (yet?) Hope I haven't jinxed myself.

nyraider56
11-21-2006, 11:14 PM
What you have related is EXACTLY what I was experiencing when I had my 2003 Envoy SLT with the air suspension. Is it related to the air suspension or something in the drive train? I don't know, but the sensation was coming from the rear of the truck. Problem for me went away when I sold it and got my 2005 Envoy Denali. It hasn't developed the problem (yet?) Hope I haven't jinxed myself.

Well I can tell you I have it w/ my 2006 Envoy Denali!!!

dziubad
11-23-2006, 03:14 AM
On my 02 Envoy SLE I get the exact same mysterious "bump" while sitting still at stop lights. I thought the guy behind me had just barely tapped my bumper. It doesn't happen all the time...maybe once a week I'll notice it and I drive mine daily. I never had it checked out...figured if it got more frequent or the bump got worse I would have it checked out. Has anybody had this checked out or know what causes it?

Envoy Fan
11-23-2006, 10:55 AM
On my 02 Envoy SLE I get the exact same mysterious "bump" while sitting still at stop lights. I thought the guy behind me had just barely tapped my bumper. It doesn't happen all the time...maybe once a week I'll notice it and I drive mine daily. I never had it checked out...figured if it got more frequent or the bump got worse I would have it checked out. Has anybody had this checked out or know what causes it?


Does your Envoy have air suspension in the rear?

blktbon20s
11-23-2006, 11:13 AM
Mine does it also and i have no air susp. just drop springs

FDZ-Denali
11-28-2006, 06:29 PM
I have a 2006 Envoy Denali with 2500 miles and just started to noticed this "bump" last week.

Same conditions:
At complete stop
After a long time parked (In the moring or after work)
Seems to come from the right side, can't say for sure, but seems from the front..

There is something going on. This is NOT normal, don't care how frequent or mild the bump is, this should not happen. Please post as soon as someone gets more info about this.

06DenaliPusha
11-28-2006, 11:51 PM
My 06 does the same thing. Also sometimes when i get down on it after i have been driving for awhile i kinda feel a rubbing on the drivers side seems like its coming from the axle not sure though has anyone else experienced this? I did the dealer thing and of course they didnt notice it.:mad:

jeranamo
03-07-2007, 09:51 PM
This is something my dad's trailblazer does at just about every complete stop. It actually does still happen even if it is not a complete stop, but you just don't notice/feel it as much. Has anyone got this figured out yet?

Wake
03-07-2007, 10:17 PM
This is something my dad's trailblazer does at just about every complete stop. It actually does still happen even if it is not a complete stop, but you just don't notice/feel it as much. Has anyone got this figured out yet?

I noticed this is an old thread but still a valid question I guess... I felt the same thing with mine shortly after buying it... I noticed one day that the spare tire was hanging very loose under the vehicle... I think there was supposed to be a pad against the frame that may have fallen out...

The spare was cranked up as far as it would go but still wasn't held tight against the underbody... I had a spare window shade that is pretty thick, I placed it on top of the spare and cranked it back up fully and the noise just about disappeared...

Check the spare, it might be worth a shot...

mswartz
03-07-2007, 10:24 PM
I had a Ranier that I leased and noticed it did the same thing, my tech said it had something to do with the load leveling. He messed with it for a day or so and I never had any issues again. I owned it for 4 or 5 months after his fix.
I now have a TBSS and have never felt the bump.

Jr_454
03-14-2007, 04:36 PM
I have the same problem I have an 05 tb ls and the shop said it was the tranny disengaging. Any one heard of this.

n0kfb
03-29-2007, 12:58 PM
My '06 Envoy with air suspension does this as well. It's going to the dealer soon for routine service, and I'll be bringing the subject up.

Wish me luck!

-- Dan Meyer

n0kfb
03-31-2007, 01:42 PM
The dealership service department once again demonstrated their incompetency.

Here is what I wrote into a document that I presented to the service writer:

"There is the feeling that the car has been bumped lightly in the rear at a light after being stopped for 20 to 30 seconds with the brake applied."

What was written on the work order:

"CUSTOMER STATES THERE IS A BUMP FEEL AFTER DRIVEN AND STOPPED FOR 20 TO 30 SECONDS AT STOP LIGHT."

"DRIVETEST VEHICLE.NO PROBLEM FOUND AT THIS TIME. SUGGEST CUSTOMER ROADTEST WIUTH FOREMAN."

The work order also states that 0.10 hours (6 minutes) were spent investigating this issue.

The dealer where I bought my Envoy has lost all of my service business. I'm trying a Chevy dealer that is closer to home. If I don't get warm fuzzy feelings from them, I may try the Cadilac/Hummer dealer near me.

It is my feeling that the root cause of this problem is the air suspension settling, due to either being mis-calibrated or a leak in a valve in the compressor assembly. I've complained about teh compressor runing too often as well, but neither the dealer nor GM can provide any typical operating parameters.

If anyone comes up with anything definitive to this problem, please post the solution!

Thank you

-- Dan Meyer

MrBigStuff
03-31-2007, 06:23 PM
The most common cause for this problem, as well as the solution, was posted back on the first page of this thread by MTPockets.

ChrisnLaurenG
04-01-2007, 03:00 AM
Ditto I have the same problem on my 06 denali

n0kfb
04-13-2007, 04:47 PM
After going round and round with both the dealer where I bought my Envoy, and GM "customer assistance" (yeah, uh-huh...they don't know squat about squat, and refuse to connect you to anyone except your dealer) my frustration level was very, very high. Since I had a little time after work, I drove to the Chevrolet dealer that is very close to work to talk to them about this (and other problems.

I walk into the service department at the end of the day, and am greeted by a service writer. His first question was what 4 wheel drive mode I was using. I use the automatic mode. He explained about how the system works, and that the problem would probably go away if I use 2wd mode. Why "customer assistance" is not aware of this, I'll never understand.

Since my problem was quite intermittent, I'm still waiting to confirm if my problem is indeed resolved.

The Chevy dealer also listened to my other issues, and seemed to be much more helpful than the dealer where I purchased the truck. Because of this, I'm taking my next routine service to the Chevrolet dealer.

Can anyone else try using 2 wheel drive instead of automatic 4wd mode, and confirming the fix?

Thanks!

-- Dan Meyer

MTPockets
04-13-2007, 05:12 PM
Dan, I don't know what type of conditions you drive in, but if it's dry or even just wet roads, I would not drive continuously in A4wd mode. Your front axle disconnect is engaged, as is the front prop shaft when you are in A4wd mode. The bump you feel, may some slack and/or tension releasing in the front drivetrain from being pushed along on dry roads, parking lots, etc... Our part-time 4x4 systems are not at all like an automotive AWD setup. My take on it is: Use it only when you need it & test it often.

Joel

ltz03
04-13-2007, 06:16 PM
it could be the tranny shifting into first gear as you come to a stop, my old 03 felt that way, basically the same symptoms

Dave
04-13-2007, 07:39 PM
I think MTPockets did provide the answer. The question is can you get the dealer to fix it and how often will you have to grease the parts. I don't even realize mine any more but I know it still happens. I drive mostly in 2wd (for reasons mentioned above) unless the weather is real crappy and I only use 4WD if the roads are real bad (6 inches of snow or so) or if I'm off road.

n0kfb
04-16-2007, 12:26 AM
What I am feeling happens AFTER BEING STOPPED FOR 20 - 30 SECONDS! It is not the transmission shifting into low gear while slowing to a stop.

The problem still exists in 2 wheel drive.

It is my feeling that the problem is somehow related to the air suspension. I'll be taking the truck to get this checked out within the next 2 weeks.

-- Dan Meyer

Envoy Fan
04-16-2007, 11:29 AM
What I am feeling happens AFTER BEING STOPPED FOR 20 - 30 SECONDS! It is not the transmission shifting into low gear while slowing to a stop.

The problem still exists in 2 wheel drive.

It is my feeling that the problem is somehow related to the air suspension. I'll be taking the truck to get this checked out within the next 2 weeks.

-- Dan Meyer

Dan, what you are describing was exactly what was occuring in my '03 Envoy SLT with air suspension. My '05 hasn't done it....yet.

sirjorge
04-16-2007, 11:48 AM
My 04 thumps, too. It has neither 4wd nor air suspension. About once a month when sitting at a light, it feels and sounds like someone kicks a soccer ball underneath the rear passenger door, and then absolutely nothing for another month or so. So weird!

n0kfb
04-17-2007, 12:43 AM
what you are describing was exactly what was occuring in my '03 Envoy SLT with air suspension.

Hi Bill

What was the solution to the problem in your '03 Envoy? Trading it in for an '05? :dielaugh:

-- Dan Meyer

n0kfb
07-21-2007, 12:12 PM
Well, it was time for another regular service, so I stopped into the Chevrolet dealer that gave me the warm fuzzies when I spoke to them in April.

I dropped off the Envoy for an oil change and "Maintenence II" (Why is it the service writers don't have a clue what is in the owners manual...), and also reported the problems I experience with the air suspension compressor running too frequently and the bump that I feel when I am sitting at a stop light in drive.

The dealer gave me a ride to the office. The service writer called me after an hour or so to say that the sway bar links on the front were shot, and would be replaced under warranty. I objected because I wondered how front sway bar links related to the problem I reported, but when he insisted this would resolve the problem I said fine. He also said that my front tires were cupping and needed a front end alignment, which I declined. When I asked about the air suspension, He said that the computer diagnostics of the air system were ran, and no problems were noted. When I pressed him for particulars of how often the compressor should run while I am commuting to work, he tried to plead ignorance by telling me that they don't get many Envoys in their shop, and Trail Blazers don't have an air suspension option, and that other Chevy trucks have a different system. He also said they could not reprduce the bump that I felt when sitting at a stop light. (The number of miles they drove the truck was under 2; I noted the in and out odometer readings). Needless to say I was steamed when I felt the bump symptom 3 blocks from the dealership.

Lessons learned:

1) Dealers are incompentent and only want your money. Treat the service department just like the sales department. The bastards are out to get everything they can from you, and do not care in the least if you return.

2) If they say you need repairs that don't make sense, don't allow the repairs to be made no matter who will be paying for the repair.

3) Take the service writer (and whoever else will go along) on a test drive to demonstrate the problem. That eliminates the "We are unable to reprduce the problem" bullcrap.

Once this bump problem is resolved, I'm seriously considering not going back to any dealer but taking my Envoy to my local independant mechanic.

If anyone knows of a dealer worthy of my patronage anywhere near the Minneapolis - Saint Paul area, please let me know.

Sign me "Still ticked off at treating me like a mushroom" :mad:

-- Dan Meyer

Envoy Fan
07-21-2007, 12:35 PM
Hi Bill

What was the solution to the problem in your '03 Envoy? Trading it in for an '05? :dielaugh:

-- Dan Meyer

The bump, and the fact the '05s had the 5.3L V8 were motovation for me to get the '05. :D

Sorry the Chevy dealer couldn't fix your bump problem. I am honestly not surprised they couldn't, as only the TB SS has the air suspension. This doesn't give them much experience at all with troubleshooting any problems. Many dealers have yet to sell their first TB SS.

If it were me, I would search for a dealership that sold both GMC and Buicks. They will have had Rainiers and Envoys in the shop and should be better able to troubleshoot the bump problem. The bigger the dealership the better.

I have only noticed a very slight bump infrequently on mine. It may even be an imaginary bump at this time :weird: Mine has been lowered since about the first day I owned it. Don't know if this has any thing to do with it or not :undecided

I have not seen any of the TB SS owners complain about the bump yet. So I don't know if they are experiencing it or not. Same with the Saab 9-7x.

n0kfb
07-23-2007, 09:50 PM
>snip<

If it were me, I would search for a dealership that sold both GMC and Buicks. They will have had Rainiers and Envoys in the shop and should be better able to troubleshoot the bump problem. The bigger the dealership the better.

>snip<


I bought my Envoy brand-new at a GMC/Buick/Pontiac dealer, and they are not much help. When I requested the name and contact information of the GM zone representative from my dealer (and also the GMC help line) they refused to give me the name and contact information.

I'll be taking the guys from the Chevy dealer for a test drive soon - hopefully later this week, to demonstrate the symptom. I may also print this thread so that they know that I'm not some sort of kook who likes to bother dealers for no reason.

I'll keep everyone posted.

-- Dan Meyer :chillpill:

n0kfb
09-05-2007, 07:17 PM
I stopped by my dealer yesterday, and went for a test drive with a service writer. At first I thought that the problem would not occur, but after a few tries the problem was reproduced, but not as pronounced as I would like.

I dropped my Envoy off this morning, and got a ride to work from my wife. They called me and said that they were finished, and they recalibrated the air suspension, and also had found a document from GM that addressed the problem; THe document ID is 1993632, and it is also known as "PIT3954E".

What the work order says is "NEC TO RECALIBRATE LEFT SIDE AIR RIDE SENSOR. PER BULLITEN #06-03-09-006A" They also drove the truck 10 miles, which is better than the last time I dropped it off and mentioned this problem.

Hopefully this issue is resolved. I didn't feel the symptom during the drive home, but I didn't have very many opportunities for the problem to appear. Expect another update - good or bad - in the coming days.

-- Dan Meyer

n0kfb
09-13-2007, 10:15 PM
Well... It seems the problem still exists, as bad as it was before. At this point, I don't know what I'm going to do about it. :cry:

Is anyone else pursuing this with GM?

-- Dan Meyer

mgh_ca
09-18-2007, 10:23 PM
I have the same thing happen to me. everytime i come to a stop. I have had my envoy into my mechanic several times and they are stumped. Im worried it might be a problem with the transmission or something. $$$$$$$

Envoy Fan
09-19-2007, 12:58 AM
I have the same thing happen to me. everytime i come to a stop. I have had my envoy into my mechanic several times and they are stumped. Im worried it might be a problem with the transmission or something. $$$$$$$

What year Envoy? Do you have rear air suspension?

Fud
09-19-2007, 01:43 PM
I havent been under my 2005 TB much yet, but a driveline thump or bump upon a stop or take-off on a 4x4/AWD is usually a dry slip yoke on the font or rear driveshaft. The driveshafts need to 'telescope' in/out to absorb chassis/drivetrain movement. A nice layer of (thick/sticky) grease in the 'telescoping' slip yoke is needed. If it drys up, the movement becomes abrubt and jerky, giving the *bump* feeling.
G/luck
Joel
__________________________________________________ _______________

I had this same "bump" when stopping with my Silverado pickup (2 wheel drive) when it only had about 10,000 miles on it. Two trips to the dealer finally fixed the problem. (A 4WD vehicle has more shafts to compound the problem so bigger and more bumps.)
My truck's problem was a dry and rusty yoke on the driveshaft. It had enough rust on the shaft that they had to use a file to remove it. They then greased the shaft and splines. That fixed it but I still have it lubed every 2nd-3rd oil change just for fun.

Fred
Ohio

dziubad
09-19-2007, 06:57 PM
I have been complaining about this "BUMP" Service dept. several times. They are never able to duplicate the problem. I always use 2wd and I do have the air suspension with 4.10 gears. 92,500 miles...

The dealership wrote on the work order
"inspect customer states at times when sitting at stops can feel a clunking in body and also at times when rolling into stop and reacell seems like trans takes off in 2nd gear and bangs into low...
Diag system has lost comunication and low voltage faults in all controllers due to failing Ignition Switch...install new switch assembly, clear codes and retest ok."
This did not fix the problem!!!!
Mine only does the "bump" when completely still at stop lights...not when I accelerate. So they didn't even really listen to me!
The next time I took it in...they were unable to duplicate the problem.
This is extremely annoying. Glad to see I'm not the only one with this problem.
Just had transmission flushed hoping that it might help...But nope...it still does it

Envoy Fan
09-19-2007, 08:14 PM
Mine only does the "bump" when completely still at stop lights...not when I accelerate. So they didn't even really listen to me!
The next time I took it in...they were unable to duplicate the problem.
This is extremely annoying. Glad to see I'm not the only one with this problem.
Just had transmission flushed hoping that it might help...But nope...it still does it

I noticed this a lot on my '03 Envoy SLT with Air Suspension. It would do it after sitting for a few hours and then when I would start up and come to a stop light it would almost with out fail bump after sitting still for 20 or so seconds.

Hasn't been noticed yet on my '05, but owners of newer than '05 have complained about this issue.

LawBlazer
09-19-2007, 11:47 PM
I have the same problem sometimes. Get a little extra bump forward just before my truck comes to a complete stop. I have a 2005 Trailblazer. It has 4wd and not the air suspension.

ss454trk
09-20-2007, 02:04 PM
Same here with my wife's 07 2wd envoy denali. at first it would do it just as you rolled off from being parked. now, it does it after the engine is started. dealer of course, "cannot duplicate". She has had people ask her what she ran over.

n0kfb
10-05-2007, 02:04 PM
I was at the dealer earlier this week for an oil change, and the service writer I worked with last time said that he spoke with another customer who reported the same symptoms as I did. He also said that GM still has no resolution for this.

I related to him that I have a theory about what is happening:

1) During the stop, the car goes nose down and tail up.

2) Once stopped, the brakes and other components continue to hold the car in a nose down/tail high attitude due to effect of the wheelbase getting shorter because the rear axle pivots in an arc. Because the rear of the vehicle is too high, the air suspension begins to vent pressure in an attempt to level itself.

3) The air suspension continues to vent. Eventually the weight of the car overcomes tire traction and/or the brake's ability to hold the rear end high, and the rear end drops abruptly.

The service writer did not show much interest in this theory.

What I believe will fix this is a recalibration of the electronics of the air suspension system. The system is much too aggressive at correcting ride height. If the system were re-calibrated to adjust ride height only after 2-3 minutes of being too high or too low, this symptom would be gone.

-- Dan Meyer

P.S. It should not be very difficult to get in touch with someone at GM who can help. For some reason this is almost impossible. It is no wonder that imported cars and trucks have a much better perception of selling quality, durable products. When you spend over $40,000 on a new vehicle, the expectation is that any problems that come up will be taken care of expediently. Unfortunately this is not that case. :mad:

Dave
10-05-2007, 02:10 PM
I would guess it was the air suspension if other people without the air suspension didn't have the same problem. My Denali has around 23k miles on it and I don't notice it any more.

big ed
10-05-2007, 03:10 PM
since I've been fooling around with my air bags trying to lower my truck, I can say yes, it is the air bags. mine had stopped or I just didn't notice it so much anymore. but since I lowered it, it has gotten worse. I guess the air bag inflate as the truck comes to a stop and the weight shifts to the front of the vehicle and once it comes to a complete stop the bags deflates slightly but rapidly enough to give it that feeling. one time at a light it was so noticeable, I looked in the mirror and saw this guy so close I knew he had hit me. I got out to find he was about 2 feet behind me but had not hit me..I was hot, for a few second's ...::hissy:...:o...:D

pWaGoN
10-08-2007, 09:54 PM
Had the same problem !! Ended up being my spare tire was loose and the tire was bumping around at stops and go !

Blusondai
10-22-2007, 12:58 PM
Like some of you I am also experiencing a mysterious Bump when holding the brakes at a stop sign/light on my Envoy

Related Specs:

2006 SLE Envoy
38000+ miles
NO Air Suspension
Mobile1 5w-30

Problem:

As stated by the original poster and several others the bump isn't felt until the Voy is at a complete stop and the Brakes are applied. You feel a jolt forward as if you have been slightly rear-ended or as if your brakes have just released your vehicle on a hill, which causes you to increase pressure on the brakes. I seriously doubt the problem is a loose spare tire, our jolts are a lot heavier than what a spare tire is capable of creating. And I seriously doubt the problem is limited to Air suspension problems seeing as I have a SLE and I don't have the air suspension.

It just started happening within the last 500 miles and I have only exprienced it between 5 and 10 times. Most of the time my radio is so loud I mistaken it for the bass, but on several occasions with the music off the jolt is still present.

One of the users stated it is possibly a dry yolk, but then another stated the TV's don't have yolks....So Which One is it!!!!

It was scary at first cause you start to get the feel the TV is going to roll into the car infront of you, but then you realize how brief the jolt is and it just becomes irritating :hissy: because it wasn't doing this before and you are still making payments....LOL

So I am hoping that with my addition information someone will be able to point all of us affected in the right direction now that we know the problem isn't just limited to Air Suspension and hopefully the TV's do have yolks so I can get mines greased again. Thanks Guys

LPlum
10-25-2007, 05:37 PM
This has also happened to my 2006 TB, I had been completely stopped for a second or two then the feeling that someone had bumped into me. After reading through 10 pages of posts, the ideas for the fix are all over the board. If it is the drive train/drive shaft moving or unloading seconds after stopping. How about an owner who's SUV does the bump often, take a video camera secure it to the under side, point it at the driveshaft and go for a drive. maybe we could all get some insight from this exercise. Thanks,
Lowell

n0kfb
11-05-2007, 11:08 AM
In light of the fact people are feeling this with both air suspension and non-air suspension, the problem isn't likely to be the air suspension system.

I've taken trips with my brother, and the first time he felt the problem he thought it was the locking rear axle unlocking; a co-worker also recognizes this as a symptom his he had in an old pickup.

Could this in fact be a problem with the optional locking rear axle?

-- Dan Meyer

the roadie
11-05-2007, 11:16 AM
...he thought it was the locking rear axle unlocking;If you were on dry pavement, there would have been no chance for you to get the 100 RPM difference between the two rear wheels that it takes to lock up the G80. But it could be a malfunctioning unit. People who feel the bump should also report if they have the G80, so we have more data points to ponder.

Envoy Fan
11-05-2007, 11:42 AM
If you were on dry pavement, there would have been no chance for you to get the 100 RPM difference between the two rear wheels that it takes to lock up the G80. But it could be a malfunctioning unit. People who feel the bump should also report if they have the G80, so we have more data points to ponder.

My '03 Envoy SLT had the G80, air suspension. Interesting, none of the TB SS guys have reported this problem yet. Maybe they never stop long enough for the issue to occur. :rolleyes:Also the TB SS has a different rear end in it.

rjgnwdc
11-06-2007, 01:08 PM
My '03 Envoy SLT had the G80, air suspension. Interesting, none of the TB SS guys have reported this problem yet. Maybe they never stop long enough for the issue to occur. :rolleyes:Also the TB SS has a different rear end in it.

It's the rear-end? cause I don't have the G80 :cry:

Jim at 73PD
12-04-2007, 05:23 PM
My 2006 Envoy Denali with 13,000 miles recently began experiencing the same “bump” when stopped. Coincidentally, it began after a sprag was replaced. I described the problem to the service writer when I took the truck in for it’s annual inspection. He directed me to a service bulletin, which declares the phenomenon as “normal” in trucks with the air suspension. I suggested that to qualify as normal it should have been present when the truck was new. He agreed but didn’t waver (a unique way of doing nothing).

I will continue to monitor the problem. I will try to isolate the transmission from the equation by shifting to neutral as I prepare to stop. I will not let GMC off this easy. There is no way a $40,000 SUV should have any sort of bump or shudder.

I will re-post when I have more to report.

Be safe.

blueblazer5_3
12-04-2007, 05:39 PM
My opinion is that under the load of stopping the vehicle (Gross Vehicle weight of 4500 lb's), the rear end twists, torqueing the rear end so that the rear axles and therefore the rear brakes become torqued under pressure. After remaining stopped, the bushings must release the pressure of this twist and therefore release the rear end and giving the "foward" motion feeling.

I've had this happen to me with the g80 and NO AIR suspension. Air suspension would have NOTHING to do with this.

The rear control arms and all the links that hold the rear end to these links are made from rubber I suppose. I have experienced similar problems with poly bushings on my other cars.

Most of the time, a rear yolk issue with lack of lubrication will give the same effect. I've noticed the issue on mine only a few hundred miles after owning it.

So, rule out the air suspension, rule out the just an Envoy thing. It come down to brakes or rear end. PERIOD!!!!

Don't bother with the dealer as they will only TRY to duplicate the issue and nothing will come of it. I do notice that it only happens in the first few miles of driving (cold or warm weather).

Don

Exit32
12-09-2007, 01:53 PM
I bought a really nice used 2004 Rainier V8 Rainier last week, and I'm thankful I found this forum and all the knowledgable people here.

My Rainier has 33,000 miles on it, and I've experienced the "bump" while stopped twice now. With the Rainier, I've got full-time AWD and rear air suspension. I've driven it about 250 miles so far, and absolutely love this vehicle, but I hope we can continue to communicate to determine the cause of our mystery bumps.

I'm fortunate to have a two-post lift in my barn and will defiinitely look at and lubricate all the splines in my Rainier's drivetrain. I haven't ruled out the air suspension as the culprit either.

Dave
12-09-2007, 05:54 PM
The bump while stopped, driveline clank while shifting and wind noise around the rear door are all "normal" operations. The dealer really can do nothing about this so the service advisor was correct. The question is that would you buy another GM car knowing what they consider normal problems? After looking around at various enthusiast sites, I must say that just about every car out there that is not bland (IE boring) has some issues that are normal.

Envoy Fan
12-09-2007, 08:32 PM
I bought a really nice used 2004 Rainier V8 Rainier last week, and I'm thankful I found this forum and all the knowledgable people here.

My Rainier has 33,000 miles on it, and I've experienced the "bump" while stopped twice now. With the Rainier, I've got full-time AWD and rear air suspension. I've driven it about 250 miles so far, and absolutely love this vehicle, but I hope we can continue to communicate to determine the cause of our mystery bumps.

I'm fortunate to have a two-post lift in my barn and will defiinitely look at and lubricate all the splines in my Rainier's drivetrain. I haven't ruled out the air suspension as the culprit either.

I'm now starting to experience the bump on my '05 Envoy Denali (19K mi) :hissy: Had this same issue with my '03 Envoy SLT with air suspension. :suicide:

Hope you come up with some sort of fix, Exit32.

So far I have not heard of the TB SS guys complaining about this issue. Maybe they never stop :undecided :laugh: The TB SS also has a different rear end, but has the air suspension.

n0kfb
12-09-2007, 11:49 PM
The bump while stopped, driveline clank while shifting and wind noise around the rear door are all "normal" ... (remaining stuff deleted)

What a load of crap. There is no way this sort of thing can be considered normal. :nono:

I think someone has been drinking too much the kool-aid supplied by GM or their "helpful" GM dealer. :crazy:

-- Dan Meyer

FrizB
12-10-2007, 05:29 PM
First off let me say thanks for all the useful information on this site. This is my first post. :thumbsup:

I thought I would quickly chime-in as I too have the infamous "bump" issue while sitting still with foot on brake petal. I started noticing it about 2 weeks ago on my 06 Denali with Air Suspension and around 16,000 miles. I too have had several ghosts rear-end me while sitting at a stop light and it is getting quite annoying.

If it ends up that this issue is "normal" and not something to cause concern, fine, but lets please find out what it is so we don't have to worry about it anymore.

Hopefully we can find some answers to this soon...
-FrizB

Envoy Fan
12-10-2007, 05:57 PM
At one time there was an extensive thread over on Edmunds about this problem. One guy said GM replaced his driveshaft on his Rainier and the problem solved (short term). I haven't been over there for about a year so don't know the long term outcome.

Exit32
12-10-2007, 07:22 PM
I was at the dealer earlier this week for an oil change, and the service writer I worked with last time said that he spoke with another customer who reported the same symptoms as I did. He also said that GM still has no resolution for this.

I related to him that I have a theory about what is happening:

1) During the stop, the car goes nose down and tail up.

2) Once stopped, the brakes and other components continue to hold the car in a nose down/tail high attitude due to effect of the wheelbase getting shorter because the rear axle pivots in an arc. Because the rear of the vehicle is too high, the air suspension begins to vent pressure in an attempt to level itself.

3) The air suspension continues to vent. Eventually the weight of the car overcomes tire traction and/or the brake's ability to hold the rear end high, and the rear end drops abruptly.

-- Dan Meyer

I was thinking about Dan's theory today and decided to see if I could get my Rainier to behave accordingly. While driving on a secondary road at about 45 mph, a traffic light turned red ahead. I braked firmly, came to complete stop with my hoof solidly planted on the brake pedal, counted to 10, then slowly released the brake pedal. The rear of the Rainier dropped noticeably and suddenly as soon as the brakes released their grip. It was so pronounced that my wife, who was in the passenger's seat, asked, "What was that all about?"

I think Dan's theory has merit. I believe the "bump" may be caused by the vehicle reverting back to its normal ride height after a brisk stop has caused the suspension to contort itself temporarily. The brakes serve to lock it in its contorted position until something gives -- most likely the rear pads slipping on the rotor due to marginal clamping force while the vehicle is stopped. The sudden unloading of the suspension is what causes the "bump." It's possible this happens to vehicles equipped with either air- or conventional-suspension systems.

I'll continue to experiment and will report new findings here. I'd like to find out if the "bump" can be prevented by applying more pressure to the brake pedal while stopped, thus locking everything more securely until its time to start moving again.

wheelieking
12-16-2007, 01:40 AM
I have an 04 ls TB and DO NOT have air susp and have experienced the bump when releasing the brake.

Envoy Fan
12-16-2007, 01:49 AM
I have an 04 ls TB and DO NOT have air susp and have experienced the bump when releasing the brake.

The bump we are experiencing is while sitting still in gear with foot on the brake.

Fud
12-16-2007, 02:14 AM
I had the same "bump" in my '03 Silverado 2WD pickup at about 10k miles from new. I went to the dealer thinking I had a bad U-joint and they claimed they had to use a file to get rust off the splined shafts at the driveshaft yokes.
They also greased the yokes and that completely cured the problem ..... until about 10k miles later. Same repair and then no bump/clunk.

Not sure if that's the problem with the TB/Envoy but it's worth a look.

Fred

Trannyman95
12-16-2007, 03:46 AM
I am glad to find a thread of this exact topic but dissappointed to see noone has really found a cause for this. Our 02 TB has been doing this for a few years now. NO rear air-ride, 3.73 gear with locking diff, 4wd, I6. It has done this since before the warranty ran out I think and of course, dealer couldnt duplicate the problem. We are now sitting at 88K miles, no change better or worse. It is exactly as described in post #1, sitting still at a stop with foot on brake pedal it feels like someone hit you from behind. My theory always was and still is the garbage Gov-Lock limited slip diff that is used. I have been building rearends for a long time and every single one of these diffs I have seen low miles or not is junk and they always get replaced with a good diff. I can see why GM uses it but its a piece of garbage and always causes issues that no dealer wants to admit. If they put in a new diff it will still act up. My thoughts are the diff is binding up and sitting relaxed with the brakes applied it unloads. The transmission still wants to spin and the wheels are held tight, so anything that CAN still move from between the two will. I know the diff will stay locked up when it shouldnt because I have been in drive-thrus before and the truck will make a very loud pinging/popping noise from the rearend like there is a real locker in the rearend or something is severerly binding. Again I have replaced a lot of these differentials and I know the dealerships do also from lots of complaints, but I think this is one that has gone unfixed for far too long, especially with this many people complaining. Now whether everyone who has this bump while sitting still with foot on brake after a quick stop does have the locking diff option would be good to know. I complained a number of times about the diff to the dealer while under warranty and they kept saying it worked fine and blah blah blah. I am a driveline specialist and some idiot pup-tech that looked at it is telling the service writer that its fine..... I gave up and even if they did replace the diff I would still be unhappy with it so if it ever really does go out I will upgrade it with a good one.

Exit32
12-16-2007, 01:58 PM
Now whether everyone who has this bump while sitting still with foot on brake after a quick stop does have the locking diff option would be good to know.

Yup. I've got the locking differential option and have experienced the mystery bump while stopped with my foot on the brake pedal.

FYI, the RPO code for the locking differential is G80 (AXLE POSITRACTION, LIMITED SLIP). Look at the list of RPO codes on the sticker in your glove compartment to find out if your vehicle is equipped with the G80 differential.

agates1272
12-17-2007, 08:36 PM
I've got an 05 Envoy SLE 4wd...no air suspension, and am experiencing the same problem. Slight bump just after stopping, and I'll go even further by saying that I feel another little bump when I lift my foot off the brake pedal. It's annoying as all hell. I hope someone finds a fix for this. The fact that GM could call this "normal" is absurd. From my early morning diesel sound to the wind noise to the bump when stopped...my $30k "Professional Grade" SUV is really starting to piss me off. Believe me, my next vehicle likely will not be a GM product unless GM gets off thier butts and starts explaining and fixing these bugs. Simply inexcusable.:weird::hissy::mad:

Oh yeah...I've also got the 3.73 with the G80...imagine that.

wheelieking
12-17-2007, 10:00 PM
I've got an 05 Envoy SLE 4wd...no air suspension, and am experiencing the same problem. Slight bump just after stopping, and I'll go even further by saying that I feel another little bump when I lift my foot off the brake pedal. It's annoying as all hell. I hope someone finds a fix for this. The fact that GM could call this "normal" is absurd. From my early morning diesel sound to the wind noise to the bump when stopped...my $30k "Professional Grade" SUV is really starting to piss me off. Believe me, my next vehicle likely will not be a GM product unless GM gets off thier butts and starts explaining and fixing these bugs. Simply inexcusable.:weird::hissy::mad:

Oh yeah...I've also got the 3.73 with the G80...imagine that.


ok i did some testing today and mine does it after braking firmly with the pedal still on most of the time. The reason i noticed it more when releasing the pedal it is slightly louder then but happens less often that way. I have an 04 ls tb without g80 3.42 and it is the 4wd I6. I am going to grease the slip in the driveshaft (if it has one) and see if that helps

edit; i also do not have air susp as mentioned earlier

Danmo
12-21-2007, 03:14 AM
i have noticed the bump feeling too when moving at slow speeds around 10-15 mph. it almost feels like the tranny is shifting into 2nd but it doesnt shift like that when im accelerating. could the yoke still be the problem?

stpolo
01-18-2008, 11:15 PM
We have this same issue. 05 Denali with Air Ride. We bought this truck used with 50,000 miles on it. We noticed the "bump" at a dead stop. We're starting to think that this "Professional Grade" truck is junk. Water pump already replaced, and then putting it in 4 Hi the truck made a huge clunk and was hard to shift out of park. Scary!!!!

mgokool
02-10-2008, 04:38 AM
Same prob on my 07' Denali....and I to have the G80 opt. Any ideas on a replacement rear end? Price ect.?

ozshadow
02-11-2008, 09:22 PM
I have an 04 Rainier I6 AWD with air suspension. This "bump" occurs to me quite frequently (3 to 4 times a week), but only on the first long stop after the truck is parked for awhile. I also have to be stopped for at least 15 or 20 seconds before it occurs.

At first, I too thought I was rear-ended. I even reached for the glove box to get my insurance card while looking in the rear view, only to see nobody behind me. Now, I've come to expect it, and press the brake pedal extra hard at long stop lights in anticipation.

Sometimes, I get 2 or 3 smaller bumps in a row, but mostly it is one larger surge.

I just got it back from picking up the Rainier at the dealer who was checking this out among other things, and of course they "could not duplicate the problem." Funny thing is, as I drove off somewhat disappointed in their futile attempt, I looped around the parking lot and stopped in a secluded area .... began counting to 20 ... and "BUMP".

Don't know how hard to press this, but it is rather annoying. My warranty runs out next summer so I want to get it resolved by then. If anybody has any info regarding a fix please do share.

Thanks,
Dave - Minneapolis



I have this exact problem:

Our 2005 Buick Rainier I6 AWD exhibits clunking every once in a while after coming to a complete stop, not every time, but sometimes multiple times. It also exhibits clunking on acceleration - almost like the vehicle is missing but it isn't. You can feel the slight clunking multiple times. It also sometimes has a low speed surge when it down shifts when coming to a stop.

blktbz
02-11-2008, 09:29 PM
While my S10 is lowered and riding on bumpstops in the rear, I actually have the same thing happening. Whether the cause is the same is doubtful, but it's almost like the spare tire swings like a pendulum, striking the rear diff. Not a hard hit, but definitely audible, and felt.:undecided

wheelieking
02-12-2008, 09:01 AM
Ok will everyone that has this problem please go out and grease their slip joints in the drive shafts. I am pretty sure that is the culprit on mine. 04 tb 4wd with NO air susp.

Something else i have been wondering....how many of you with this issue still have stock shocks? Possibly the valving as it settles? The reason i ask is the other day we went to get groceries and I had the hatch open unloading it at home and had it almost empty and had to lean on it to get the last sack. my weight leaning on the rear bumper caused the "bump" I have been hearing. ??? I have since greased the shaft and will report back soon.

BUC NASTY
02-12-2008, 09:09 PM
I dont know what you guys are talking about. My truck is 6 years old and has a G80. I never ever felt whatever it is that you guys experienced. :coffee

Envoy Fan
02-13-2008, 12:06 PM
I dont know what you guys are talking about. My truck is 6 years old and has a G80. I never ever felt whatever it is that you guys experienced. :coffee

You also don't have air suspension in the rear. The issue seems to occur with this "feature". Be glad you don't have the problem.

wheelieking
02-13-2008, 03:31 PM
You also don't have air suspension in the rear. The issue seems to occur with this "feature". Be glad you don't have the problem.



Aparently no one is listening to me when i say I have the problem also and i DO NOT have air suspension!! Please read my post above.

Clockman06LT
02-13-2008, 06:37 PM
My 06 LT acts the same way and it DOES NOT have air suspension. I just avoid hard stops by letting off the brake slightly before coming to a complete stop. This seems to keep the bump from happening. No G80.

My :m2:.

BUC NASTY
02-16-2008, 01:26 PM
You also don't have air suspension in the rear. The issue seems to occur with this "feature". Be glad you don't have the problem.

Thank god!

Im curious what is the point of putting air suspension on the rear? Does it help at all?

curtplat
03-23-2008, 12:04 PM
I have the same issue with my 06TB. Coil springs, not AB suspension. Truck going in tomorrow for service. 29K

SCs_5th_Gen
03-24-2008, 06:25 PM
I have had it a couple times also and I do have 4 wheel drive.

jmoudry
03-25-2008, 10:56 AM
Just felt the "bump" last night. It happened a few seconds after I was stopped. Seemed like it was comming from the right rear. I do not have air bags or 4WD. When do the issues end with these things:hissy:

I have had it for 3 months and have had the engine replaced, now I have a coolant leak, the side windows are scratching and now the bump.

redz71tahoe
04-20-2008, 02:49 AM
I am bound and determined to get to the bottom of this. My wife says she hears/feels “the Bump” as described by the original poster almost every day on her way to work. I thought she was crazy until I found this post. I drive this thing about ˝ as much as her and I have never felt or heard “the Bump” quite as described. I have pretty much ruled out driving style, sometimes I drive it like it’s stolen, sometimes I baby it.
Now what I have heard is the air conditioner compressor kicking in (also comes when your climate control is set to defrost) and in my envoy it is a loud clunk. The ac compressor kicks in and out every 15 to 60 seconds depending on the climate control fan speed setting, humidity level, and engine rpm. There have been quite a few times when like stated here; a few seconds after stopping I hear the clunk.
Now I also hear it then the truck is in park in my driveway.
since my wife don't listen to me, is there someone else out there who experiences “the Bump” regularly who can just humor me and test this by turning the climate control completely off and see if the problem disappears, or turn on the AC with the truck in park, keeping the fan speed low will cycle the compressor on and off faster, tell us what you hear
Thanks

Dave
04-20-2008, 03:05 AM
My Denali now has around 32k on it and I haven't noticed the bump for awhile. Of course my wife mostly drives it now though. None of my other cars does it though so I'm sure I would definitely notice it when I drive the Denali though.

Coach Steve
04-20-2008, 04:24 AM
Just felt the "bump" last night. It happened a few seconds after I was stopped. Seemed like it was comming from the right rear. I do not have air bags or 4WD. When do the issues end with these things:hissy:

I have had it for 3 months and have had the engine replaced, now I have a coolant leak, the side windows are scratching and now the bump.
So they did end up replacing your engine afterall? Details man, we need details. Did you have to resort to threatening them? What, how, how much, etc.

Steve in Chandler

tschneider4x4
11-07-2008, 01:52 AM
Just thinking out loud after reading all 14 pages of data. My 04 Envoy used to do the "surge" when in D at a stop light occasionally, but now has a extremely powerful shudder when stopped in D at a stop light (or in the driveway, etc. for that matter). I am thinking that the Torque Converter (TC) for whatever reason is not disengaging when "loaded" and creating too much for the brakes to hold constantly (similar to "power braking"). So, after enough time, and when the engine starts to wear, eventually the loaded TC is too much for the engine to maintain smooth idle so it starts to shudder as the TC and engine are battling for position (i.e. engine slows, TC starts to release but then can decide between releasing and holding so "shuddering" results).

Okay, it may be far fetched, but I thought I would at least offer a different idea from those already posed.

Thanks,

Todd

Monoposto_Racer
11-19-2008, 10:40 PM
There seems to be a common theme here, but it is also clear that there are multiple phenomena being discussed on this thread and plenty of talking at cross-purposes. I too have the infamous "bump" and have had it since new (2002 Envoy SLT, air suspension). A few posters here have accurately described the issue: sitting fully stopped at a traffic light in D, minding your own business when there is this funny little lurch. It feels like you didn't have the brakes on quite hard enough and they just slipped a little. Although it is noticeable, it is not particularly alarming and I never regarded this as a problem, more a curiosity. It was curiosity that drove me to read 14 pages of this thread to see if anybody had an explanation - not! Most of the "fixes" discussed here are actually fixes for some other problem. The most plausible explanation that I have read is that the chassis remains in a nose-down stance after a firm stop and at some point the air suspension tries to level it up. That doesn't really feel like what is going on and certainly doesn't explain why it would occur on coil sprung models (although it is not entirely clear that they are all describing the same issue). Personally, I always assumed that it had something to do with the ABS system trying to rebalance itself after a prolonged period of brake application (perhaps due to some sort of internal leakage or bleed-down), especially since it seems to be accompanied by a slight movement of the brake pedal, although I could be imagining that part. Anybody have any knowledge or experience to support or refute that idea?

Inconspicuous
01-28-2009, 10:25 PM
Kicking this one to the top.

Just bought an '07 Trailblazer, have owned a '99 Tahoe for the last 5 years. The Tahoe had the thump from the rear that was very noticeable right away when I first got it. Found that it was indeed the driveshaft slip-yoke at the rear output of the transmission that had dried up and was binding.

Those of you that are saying that it is happening while you're just sitting there at a traffic light and still dismissing this as being the problem are likely incorrect. This has been a common problem for GM vehicles for a long time. They have tried curing it with nickel plated slip-yokes, as they are smoother on the surface and are supposed to resist binding, but apparently that change didn't really help. The thump can occur without having the vehicle move at all, it only takes a slight movement of the yoke on the splines to cause a noticeable thump. I've found that coating the splines with anti-seize paste works well, but I end up having to do it with each oil change on the Tahoe.

The only reason I found this thread is because I had to do a search on it to see if others were having this same issue. I was expecting this problem to have been resolved by GM engineers by now, so I was quite surprised to hear/feel that same familiar thump in the '07. :rolleyes:

canetherton
01-29-2009, 10:20 PM
Some of you have described an issue similar to mine. As I slow down almost to a stop, I get a little lurch. I had it in the dealer to get my tranny flushed and had them check it out. They drove it arround and said that it was a dirty throttle body. I haven't got it cleaned yet so I will see if it helps when I can do it. :m2:

gelato
02-02-2009, 03:06 AM
lots of postulating about the mystery driveline bump, but disappointingly no consensus on diagnosing the root cause :(

i too have experienced the bump under the following conditions:
after a cold start (i.e. vehicle sitting overnight, startup to go to work).
within the first 2 miles of my commute there is a stoplight that i usually catch, so i need to come to a complete stop while waiting for the green.
while waiting at the stoplight, i experience the "bump" sensation while the transmission is in drive and my foot is on the brake firmly.
the bump sensation feels akin to shifting on-the-fly from neutral to drive at an elevated engine rpm (mini "neutral-drop"), however the vehicle cannot move forward because the brakes are engaged (hence the chassis pitches downward ever so slightly).
there are no obvious audible sounds associated with the "bump" (no scraping, no clanking, no banging).
in my experience, the bump only occurs once (within 3 minutes of cold starting).

my vehicle specs:
2003 envoy slt
4x4
g80 locking rear diff (3.73)
trans mode selector in 2wd
rear airbag suspension (load leveler)
no trouble codes or idiot lights present
72,000 mi

my 2cts:
i don't buy the connection to the air suspension theory.
any venting of the airbags would be accompanied by a sharp and audible "hissing" (due to the magnitude of the bump sensation).
any filling of the airbags would be accompanied by the loud air compressor kicking in (which does not occur).
the vehicle does not come to a severe angle when i stop, therefore the rear suspension position sensors are not engaged (this is not an emergency stop, the front end does not dive excessively, it is a stop under normal conditions and speeds).

also dont believe it is associated with worn u-joints. worn universal joints would exhibit an audible and tactile bump sensation during every start-stop situation (i.e. stoplight traffic). worn u-joints are especially evident during forward-reverse situations. i have not experienced this behavior with the "mystery bump".

not so sure about the slip yoke theory either. the road i travel on is very smooth, so there is not much suspension movement which would require the yokes to be displaced significantly. keep in mind the mystery bump occurs while sitting at a stoplight - a static situation. if the yokes were sticking, i would expect to experience the bump more frequently in dynamic/moving suspension situations (which i do not).

my only educated guess would be that the bump has something to do with the transmission. it feels as if the transmission is decoupling from a high pressure situation to a low pressure situation. the drivetrain cycles from a high tension state (rear driveshaft torque loaded), to low tension state (rear driveshaft torque relieved). hence the sensation of the chassis/rearend pitching downward slightly (rear end of the vehicle settles).

does the fact that the engine rpm's are in the cold-start-fast-idle mode have anything to do with this?
does this transmission have a lockup torque converter?
is it possible that the torque convertor is "sticking" and abruptly unlocking, thus causing the bump sensation?
is it possible that excess transmission line pressure is being switched from high-to-low inside the transmission, thus causing the bump feeling?

this post is raising more questions than answers. but maybe someone can quantify this information and deduce a more scientific answer (paging GMT360...). :confused:

so far, no damage has resulted from the mystery bump behavior.

Inconspicuous
02-08-2009, 09:55 PM
not so sure about the slip yoke theory either. the road i travel on is very smooth, so there is not much suspension movement which would require the yokes to be displaced significantly. keep in mind the mystery bump occurs while sitting at a stoplight - a static situation. if the yokes were sticking, i would expect to experience the bump more frequently in dynamic/moving suspension situations (which i do not).

The slip yoke is constantly moving on the output shaft of the transmission while the vehicle is in motion, smooth roads or rough roads. Think about it this way: pretty much any time the front or rear shock absorbers/springs move up or down in tandem, the slip yoke is moving one way or the other on the output shaft, .

Whenever your vehicle's body "pitches down" no matter how slight the movement, the slip yoke is moving on the output shaft.

When you come to a stop, the rear of the vehicle's body comes up, and the front goes downward. If the slip yoke is not lubricated, it will bind and stick momentarily, and the body of the vehicle will settle and place enough force on the yoke to break the bind. This can happen right after the stop, or even a few seconds after the stop. If I hold the brakes tight enough, I can prevent the thump until I release and get ready to move forward.

Do the experiment on your own. Take out the driveshaft, spread some anti-seize on the splines of the yoke and put it back in. Your thumping will be gone.

The reason it is only happening when your vehicle is cold is likely because of the change in dynamics of the friction between the two pieces between when they are warm or cold.

peteinsonj
02-16-2009, 01:54 PM
In the last couple of weeks my '08 9-7x with 11k miles has been doing this exact thing.

Be curious what the dealer might know about it, I assume he sees a lot fewer of this body truck than the average Chevy or GMC dealer.

Good info! Pete

n0kfb
02-16-2009, 08:14 PM
>snip<

...This has been a common problem for GM vehicles for a long time...

>snip<

Why didn't any of the dealers have a clue, even after the issue was brought to their attention on multiple visits and one test drive?

The problem has been gone since my 60,000 service that was not performed at a dealer, but at a local independent garage. I suspect that lubricating the driveshaft splines splines is what resolved the problem.

-- Dan Meyer :coffee

the roadie
02-16-2009, 08:29 PM
Why didn't any of the dealers have a clue...Some (note: not all) dealers couldn't catch a clue during the height of the clue mating season under a full clue moon on the clue mating grounds if they smeared their bodies with clue pheromones, wore clue bondage gear and did the clue mating dance, surrounded on all sides by thousands of raging, horny clues.

Yes, that's how I truly feel. :tiphat

keith
02-25-2009, 06:23 PM
I don't know if this helps anyone, but I've had the same problem intermittantly, even when I slow down easy to a full stop. This problem was driving me nuts ! so I began to watch the tach closely and even tried putting
the vehicle in neutral as I tried different ranges from stopping hard to nearly rolling to a stop. This is what I found : During the "bump" while the vehicle was in "drive", the tach jumps up just a little at near complete stop, and after a complete stop, with a noticeable bump. When in neutral or 1st gear
the vehicle stops smooth as glass every time, so I'm wondering if the trans
is having a late shift down to 1st gear ? I brought my envoy to the dealer to have the radiator fan clutch replaced, during which they had to reset the vehicle computer...I've never even had the slightest hint of that problem since.
K.G.

CrzyFireman82
02-26-2009, 11:59 PM
yeah i have the same problem in mine. front/rear brakes and rotors recently replaced. i was told it could be the transmision out put shaft but that came back ok. then someone said motor moutns but they are tight. so i have the same problem. hopefuly not to expensive to fix

Mentalmadness
02-27-2009, 12:36 AM
Thinking about the yoke theroy, and i really like it. I mean I can understand how it works and the binding and then with a settling down of the truck the binding gives way....

I think I'll go lube my shaft

SBUBandit
03-25-2009, 01:07 PM
Sound exactly like the problem my Grand Am had last spring. Mine ended up being the real wheel cylinders, they were sticking and then would suddenly let loose and thud back into place and the car would lurch just a hair, felt exactly like i was being bumped

sse1990
03-25-2009, 01:38 PM
I read through as many pages as I could and I have also experienced this with my 06 Rainier. Not often, just once and a while. What I did notice is when I feel the bump, I look out the back window and align a rear defroster line with something like a building and notice my rear goes down right after the bump. Sometimes it is 2 bumps. So I always figured it was the air suspension.

EvoSaab
03-25-2009, 08:20 PM
I own a 2006 Saab 9-7x 5.3 its AWD and has air suspension. The following post describes our issue exactly.

"I have an 04 Rainier I6 AWD with air suspension. This "bump" occurs to me quite frequently (3 to 4 times a week), but only on the first long stop after the truck is parked for awhile. I also have to be stopped for at least 15 or 20 seconds before it occurs.

At first, I too thought I was rear-ended. I even reached for the glove box to get my insurance card while looking in the rear view, only to see nobody behind me. Now, I've come to expect it, and press the brake pedal extra hard at long stop lights in anticipation.

Sometimes, I get 2 or 3 smaller bumps in a row, but mostly it is one larger surge."

First I want to say the Saab dealership has been great to deal and are a 1st class bunch of guys to work with. Unfortunately they have yet to duplicate the issue on any test drives. Its intermittent and I couldn't see how they could duplicate it in the shop. They did perform TSB 13823. This included replacing of the yoke, ujoint and prop shaft however we still have the problem.

Truck is going in to the dealership again next Monday, I'll update on how that goes. Thankfully this truck came with a 5yr 50,000 mile warranty and covers loaners, 2009 9-3 Aeros AWD are fun loaner vehicles. :)

Some crazy ideas I'm going to try this weekend is jacking up the rear of the truck in the driveway just a bit, apply the brakes, release the jack slowly, and then see if I can replicate the problem. Its driving my wife nuts :crazy:

Denali n DOO
03-25-2009, 08:30 PM
yep. I had the mystery bump once today. I'll be watching for the update...

babe
03-28-2009, 03:12 PM
I think it has somthing to do with the air ride system it self adjust with no load at a stop.Have you ever watch a tractor trailer at stop light with no trailer you see the rear axel air bags raise.That's what I think!

Robert1101
03-28-2009, 03:32 PM
Mine has always downshifted into 1st just prior to coming to a full stop. I guess that could be called a "bump".

CrzyFireman82
04-01-2009, 10:33 PM
03 tb ls....i to experience the bumb at a stop or slowed movement. ive replaced both front and rear brakes and rotors. also new bushing on the sway bar links. ive taken it to the dealership and they said everything looks fine. the trans output shaft was suggested but that to was fine. others say it could be a u joint or trans itself. but idk. i experince it every time i stop. so idk any help would be great

cdpyjs
04-01-2009, 10:52 PM
Some (note: not all) dealers couldn't catch a clue during the height of the clue mating season under a full clue moon on the clue mating grounds if they smeared their bodies with clue pheromones, wore clue bondage gear and did the clue mating dance, surrounded on all sides by thousands of raging, horny clues.

Yes, that's how I truly feel. :tiphatwow...wtf...someone needs to cut the roadie off....:rotfl::rotfl:

cdpyjs
04-01-2009, 10:54 PM
I don't know if this helps anyone, but I've had the same problem intermittantly, even when I slow down easy to a full stop. This problem was driving me nuts ! so I began to watch the tach closely and even tried putting
the vehicle in neutral as I tried different ranges from stopping hard to nearly rolling to a stop. This is what I found : During the "bump" while the vehicle was in "drive", the tach jumps up just a little at near complete stop, and after a complete stop, with a noticeable bump. When in neutral or 1st gear
the vehicle stops smooth as glass every time, so I'm wondering if the trans
is having a late shift down to 1st gear ? I brought my envoy to the dealer to have the radiator fan clutch replaced, during which they had to reset the vehicle computer...I've never even had the slightest hint of that problem since.
K.G.Ok guys, I haven't read this entire thread, just the last couple pages. This above sounds the most accurate. My father in-law worked for Chrysler trans plant and I have drove a few test vehicles (Jeeps). One was doing this exact same thing. I would come to a stop and about 1-2 seconds later, thud. It was shifting down into first gear after the stop and not while decelerating. I'm not sure exactly what the cause was, maybe a bad shift solenoid, or a PCM problem. Start with those.:m2:

EvoSaab
04-07-2009, 03:44 PM
I own a 2006 Saab 9-7x 5.3 its AWD and has air suspension. The following post describes our issue exactly.

"I have an 04 Rainier I6 AWD with air suspension. This "bump" occurs to me quite frequently (3 to 4 times a week), but only on the first long stop after the truck is parked for awhile. I also have to be stopped for at least 15 or 20 seconds before it occurs.

At first, I too thought I was rear-ended. I even reached for the glove box to get my insurance card while looking in the rear view, only to see nobody behind me. Now, I've come to expect it, and press the brake pedal extra hard at long stop lights in anticipation.

Sometimes, I get 2 or 3 smaller bumps in a row, but mostly it is one larger surge."

First I want to say the Saab dealership has been great to deal and are a 1st class bunch of guys to work with. Unfortunately they have yet to duplicate the issue on any test drives. Its intermittent and I couldn't see how they could duplicate it in the shop. They did perform TSB 13823. This included replacing of the yoke, ujoint and prop shaft however we still have the problem.

Truck is going in to the dealership again next Monday, I'll update on how that goes. Thankfully this truck came with a 5yr 50,000 mile warranty and covers loaners, 2009 9-3 Aeros AWD are fun loaner vehicles. :)

Some crazy ideas I'm going to try this weekend is jacking up the rear of the truck in the driveway just a bit, apply the brakes, release the jack slowly, and then see if I can replicate the problem. Its driving my wife nuts :crazy:

Yes I just quoted myself! :crazy:

Update from picking truck up from Saab: They were still unable to replicate our issue however, before I could swing over to the shop the mechanics called the Saab Tech line and they decided to try replacing the output shaft. BAM! No more random thuds at stoplights! They said the output shaft was pretty rusty.

Envoy Fan
04-07-2009, 04:37 PM
Yes I just quoted myself! :crazy:

Update from picking truck up from Saab: They were still unable to replicate our issue however, before I could swing over to the shop the mechanics called the Saab Tech line and they decided to try replacing the output shaft. BAM! No more random thuds at stoplights! They said the output shaft was pretty rusty.


What is the output shaft? Drive shaft or ????:undecided

EvoSaab
04-07-2009, 05:48 PM
What is the output shaft? Drive shaft or ????:undecided

Well, I didn't see the part first hand so I am assuming its the output shaft from the transmission. They already performed TSB 138232 on an earlier visit which I was told included driveshaft slip-yolk and ujoints? That didn't help so this time the replaced the output shaft. Something tells me once the grease wears out or gets old the problem will come back again. :bonk:

cdpyjs
04-07-2009, 07:05 PM
Well, I didn't see the part first hand so I am assuming its the output shaft from the transmission. They already performed TSB 138232 on an earlier visit which I was told included driveshaft slip-yolk and ujoints? That didn't help so this time the replaced the output shaft. Something tells me once the grease wears out or gets old the problem will come back again. :bonk:The output shaft is the splined shaft coming out of the trans, and the slip yoke attaches to it, then to the driveshaft. Wonder if they caused the problem when they did the TSB for the slip yoke??:undecided

EvoSaab
04-12-2009, 11:56 AM
The output shaft is the splined shaft coming out of the trans, and the slip yoke attaches to it, then to the driveshaft. Wonder if they caused the problem when they did the TSB for the slip yoke??:undecided

No they didn't cause it. I had this problem before ever bringing it in to Saab. The TSB was their first attempt to fix this issue and it made no difference, my second visit they gave the truck back to me saying they could never replicate issue, the last visit the replaced the output shaft and that made the difference.

Over a week of driving and the issue has gone away completely, Saab solved it, lets hope it doesn't come back.

Envoy Fan
04-12-2009, 02:14 PM
What all is involved in replacing the output shaft? Is this an easy DIY or does it need dealer or shop to replace the shaft?

TXBlazer
04-12-2009, 02:32 PM
I'm thinking all the owners that are having the "bump" while stopped have the air suspension.:undecided

I've also had the mystery bump while completely stopped with my foot on the brake. The tach actually jumped up a bit and the truck tried to surge forward, almost like I was hit from behind but without being hit. The slight surge on the tach was a little odd, almost like the truck was starting to take off without me being ready to go.

My truck doesn't have air ride, go figure!!

the roadie
04-12-2009, 02:58 PM
I've also had the mystery bump while completely stopped with my foot on the brake. The tach actually jumped up a bit and the truck tried to surge forward, almost like I was hit from behind but without being hit. The slight surge on the tach was a little odd, almost like the truck was starting to take off without me being ready to go.

My truck doesn't have air ride, go figure!!My experience exactly. No air ride, and I believe the air ride compressor works too slowly to give you a jolt like that anyway. I've always discounted that theory.

My own belief is there's three causes that can give us this effect. One is the known driveshaft slip joint issue of needing regular lubrication. The slight nosedive on deceleration requires the driveshaft to lengthen. When you come to a stop and the rear suspension settles down, the driveshaft has to shorten, and if it's sticky, you get a bump.

The second cause (I think) is the age-old dirty throttle body issue. As you decelerate, even in neutral, the tables in the PCM don't allow the idle RPM to go down to the lowest setting of 600 RPM until your speed is zero MPH. You can see this if you throw it in neutral at 20-30 MPH. The idle speed isn't set to drop before your speed decays on its own. So when you come to a stop, your idle is higher than 600. Then you stop, the PCM sets the idle to minimum, your AC is on, the dirty throttle body syndrome causes (sometimes) a jump in RPM to 1200 as it overshoots, and that bumps you through the transmission.

And the third totally plausible possibility is the delayed downshift to 1st. I could check this out by driving around for a bit with EFILive and datalogging turned on to get data on the downshift point. This cause could give a much sharper jolt than a dirty throttle body engine blip, so it's a compelling story.

My bumps are almost always accompanied by the RPM blip, and cleaning the throttle body has been the cure (for me.) Other people observe the no-RPM issue and I believe the driveshaft splined slip joint lube will be their cure.

Army Mike
04-13-2009, 02:37 AM
I am glad you brought this up and I hope you read what MTPockets had to say....Some damn good advice, nice to hear it from a pro... I have the same problem and now I know what I need to fix it....Thanks MT

tomas216
05-28-2009, 01:15 AM
everyone go lube their shaft :thx

twinsdaddy24
05-28-2009, 11:01 PM
[QUOTE=MTPockets;91308]I havent been under my 2005 TB much yet, but a driveline thump or bump upon a stop or take-off on a 4x4/AWD is usually a dry slip yoke on the font or rear driveshaft. The driveshafts need to 'telescope' in/out to absorb chassis/drivetrain movement. A nice layer of (thick/sticky) grease in the 'telescoping' slip yoke is needed. If it drys up, the movement becomes abrubt and jerky, giving the *bump* feeling. Not sure if the envoy has grease fittings or not on the driveshafts (look for rubber boots on the driveshafts), but most require the driveshafts to be dropped, boot clamps cut, driveshaft serperated, splines cleaned, regreased and the hole thing reassembled and reinstalled with new boot clamps. The driveshafts are typically flanged & bolted at both ends for easy removal. You also need to mark the driveshaft halves anytime you seperate it @ the splines so you reassemble it the same way for proper balancing. Slip yokes are one of those 4x4 maintenance items that never seem to get listed anywhere.:duh:

Bingo:thumbsup:

Very common problem in the Jeep world too

Envoy Fan
05-29-2009, 12:53 PM
[QUOTE=MTPockets;91308]I havent been under my 2005 TB much yet, but a driveline thump or bump upon a stop or take-off on a 4x4/AWD is usually a dry slip yoke on the font or rear driveshaft. The driveshafts need to 'telescope' in/out to absorb chassis/drivetrain movement. A nice layer of (thick/sticky) grease in the 'telescoping' slip yoke is needed. If it drys up, the movement becomes abrubt and jerky, giving the *bump* feeling. Not sure if the envoy has grease fittings or not on the driveshafts (look for rubber boots on the driveshafts), but most require the driveshafts to be dropped, boot clamps cut, driveshaft serperated, splines cleaned, regreased and the hole thing reassembled and reinstalled with new boot clamps. The driveshafts are typically flanged & bolted at both ends for easy removal. You also need to mark the driveshaft halves anytime you seperate it @ the splines so you reassemble it the same way for proper balancing. Slip yokes are one of those 4x4 maintenance items that never seem to get listed anywhere.:duh:

Bingo:thumbsup:

Very common problem in the Jeep world too

:offtopic: What ever happened to member MTPockets? Just quit posting one day :worried: He had a lot of good tech info :hail:

Denali n DOO
05-29-2009, 07:08 PM
check his contact info and send him an e mail??:undecided.......

Olive Oil
07-08-2009, 05:51 PM
When this first happened to me, it scared the poop out of me. I thought maybe the breaks were going out. I call it shuddering. It almost feels like the breaks are slipping. Did you ever get a lamens terms of what the problem is?

Uber
09-16-2009, 12:17 AM
ha... guess I have to contribute!
It appears that you have not posted on our forums in several weeks. Please take a few moments to perhaps ask a question, help provide a solution or just engage in a conversation with another member in any one of our forums. Thanks!

2004 4.2L SLT with air ride

Yes.... I have the magic thump in D after stopping at the lights every morning....I think I would miss it now....like part of my routine:bonk:... I have complained to every dealer at every service.... never find a solution...

it's in the shop right now getting a new air con condenser under warranty.... apparently the fact that the hydraulic tappets have decided to make it sound like a diesel in the last two weeks is also totally "normal". The service writer actually said to me that is hard to explain to customers..."people don't understand...they seem to think that just becuse it starts suddenly then it is a problem....they say...but it didn't do it before"

As I have read the whole thread I concur that the service writers are indeed as clueless as a clueless thing in a clueless factory that makes clueless stuff for clueless day.

I will now print out the entire thread and drive back the crappy Uplander with the wobbly front wheels that they gave me as a loaner and hand it to them.

I believe I can rest assured they will continue to totally (and probably intentionally) misunderstand the problem...:duh:

the roadie
09-16-2009, 12:44 AM
As I have read the whole thread I concur that the service writers are indeed as clueless as a clueless thing in a clueless factory that makes clueless stuff for clueless day.My favorite rant in a similar vein is:

You couldn't get a clue during the height of the clue mating season on the clue mating grounds if you smeared your body with clue pheromones, wore clue bondage gear and did the clue mating dance under a full clue moon, surrounded on all sides by thousands of raging, horny clues.

Uber
09-16-2009, 08:37 PM
What I found today.... looks like it is a known issue....:undecided



Bulletin No: 07-04-17-001D

Date: May 18, 2009

TECHNICAL

Subject:
EI07148 - Bump/Thump Heard/Felt from Driveline or Rear Suspension after Braking (Replace Output Shaft Yoke)

Models:
2004-2007 Buick Rainier
2004-2009 GMC Envoy,Envoy XL
2004-2005 GMC Envoy XUV
2002-2004 Oldsmobile Bravada
2005-2009 Saab 9-7X Models
with Automatic Level Control Rear Suspension (RPO G67)
_______________________________________________

This Bulletin is being revised to update the labor time for 4WD/AWD applications. Please discard Corporate Bulletin Number 07-04-001C (section 04 -- Driveline/Axle)
_______________________________________________

Condition:
Some customers may comment on a bump or thump noise heard from the rear suspension or felt in the floor. The information below will affect vehicles with G67 Automatic Level Control rear suspension. This noise will typically occur at traffic lights after rapid stops. This noise is due to a combination of the rear electronic suspension attempting to level the vehicle and the driveline becoming unbound after these rapid stops.

Correction:
Contact your DVM (District Service Manager) for approval prior to making any repairs. 4WD vehicles - Replace the Output Shaft of the Transfer Case and the Drive Shaft Yoke and grease with p/n 12345879 (in Canada use p/n 10953511). Reinstall and evaluate operation. 2WD Vehicles - replace the Output Shaft of the Transmission and Drive Shaft Yoke.Reinstall and evaluate operation.

Unpublished Labor guide:
F9721*
Rear Propsaft Output and Yoke Replace
4WD 4.2 hrs
2WD 8.0 hrs

guitarplayr92m
09-16-2009, 09:18 PM
I do not have the rear leveling suspension, and i get this annoying occurance every day! It is REALLY bad when going down a hill and stopping suddenly, the whole truck shakes side to side, pretty violently.

dig828
09-16-2009, 10:49 PM
I do not have the rear leveling suspension, and i get this annoying occurance every day! It is REALLY bad when going down a hill and stopping suddenly, the whole truck shakes side to side, pretty violently.

:undecided :iagree:Me too,(no rear leveling)but happens occassionally, not violently. Actually hasn't happened in a few months....guess I should be prepared for next occurrence

rjmyklebust
10-09-2009, 10:05 PM
I just found this thread tonight after looking for it for 6 months. I guess I am bad at looking.

I am pumped to go try a few of these things. I am thinking my shaft needs be lubed and is binding when I stop going down to my first stop light in the morning. As the air bags let air out more tension is applied to rear brakes. When they release I feel a pop and the rear end drops.

I will lube my shaft this weekend. Maybe I will need my roomate to help me Jack it up before I start. I will post the results after a few trips to work next week.

parrothead1
10-09-2009, 11:07 PM
I picked up my Trailblazer yesterday after it set P0135 for O2 sensor, and had a low-power and backfire condition shortly after startup. The new o2 sensor fixed this problem, but on I-95 in VERY HEAVY traffic in Springfield, VA, I was creeping along at about 1mph when the engine felt like it was bogging down for a split second. The engine then (with no foot on brake or gas) seemed to overcorrect and the tach jumped almost to 2k rpm for a second, accompanied by a sound similar to an '82 Buick Lesabre dieseling. (Used to drive one in the 1990s) The vehicle lurched forward about 10 feet before I hit the brake, and then everything returned to normal. I thought I was rear-ended too, but the guy behind me in a tiny toyota had no damage and no reaction. I found no damage when I got home. I had a 2000 Grand Prix GT with a 3800 that did this when the MAF sensor was going out on it. Does my vehicle have an MAF? Anyone else had this problem accompanied with the engine and the dieseling sound? :confused:

RainierRVer
10-09-2009, 11:20 PM
I had this issue too; until I installed an auxiliary transmission cooler because I tow frequently. Problem pretty much disappeared for me after transmission cooler was installed. Given that I have the auto leveling rear suspension and nothing changed with that, I don't think the problem has anything to do with the auto leveling. Since most people seem to report that the problem occurs at the first stop lights on a morning drive, I doubt that its a trans temp issue. Maybe a pressure or trans fluid capacity issue? :undecided

rrufast
10-23-2009, 05:36 AM
Can anyone confirm that the TB's have grease fittings for greasing the slip yoke or do we have to remove/replace? I'm willing to bet the later...

Hey ROADIE... you saids about a 20 minute fix in another thread... (http://forums.trailvoy.com/showpost.php?p=841813&postcount=3)

Care to elaborate? Thanks!


I havent been under my 2005 TB much yet, but a driveline thump or bump upon a stop or take-off on a 4x4/AWD is usually a dry slip yoke on the font or rear driveshaft. The driveshafts need to 'telescope' in/out to absorb chassis/drivetrain movement. A nice layer of (thick/sticky) grease in the 'telescoping' slip yoke is needed. If it drys up, the movement becomes abrubt and jerky, giving the *bump* feeling. Not sure if the envoy has grease fittings or not on the driveshafts (look for rubber boots on the driveshafts), but most require the driveshafts to be dropped, boot clamps cut, driveshaft serperated, splines cleaned, regreased and the hole thing reassembled and reinstalled with new boot clamps. The driveshafts are typically flanged & bolted at both ends for easy removal. You also need to mark the driveshaft halves anytime you seperate it @ the splines so you reassemble it the same way for proper balancing. Slip yokes are one of those 4x4 maintenance items that never seem to get listed anywhere.:duh:

G/luck
Joel

the roadie
10-23-2009, 11:20 AM
No grease fittings. Just remove four bolts from the rear U-joint attachment, slide the driveshaft forward 1/2", drop it down at the back, pull out, and voila!

http://www.roadie.org/driveshaftding2.jpg

http://www.roadie.org/ds2.jpg

http://www.roadie.org/axle112.jpg

rrufast
10-23-2009, 05:32 PM
Thanks for the prompt replay.. and thanks even more for the pics.. I'll get around to this soon I hope....

sdadams
10-31-2009, 12:33 AM
There is a TSB out that requires replacement of the driveshaft yoke that connects to the output shaft of the transmission. Apparently the tolerences of the driveshaft yoke to the spline is too tight causing binding. Mine was replaced at 30K miles. Symptoms were as you described.

Steve

Denali n DOO
10-31-2009, 09:13 AM
So should this repair (defect) be covered by GM Warranty???? :undecided

the roadie
10-31-2009, 11:04 AM
Only if the TSB says it is. A Technical Service Bulletin isn't always (or even mostly) an indication of a warranty or recall issue. It's just extra technical instructions to GM technicians and TSB subscribers how to fix difficult or subtle problems. Like this one, where everything from the PCM to the transmission to the air suspension system is a suspect far before anybody homed in on the slip yoke.

sdadams
10-31-2009, 12:50 PM
Mine was, no questions asked.

Steve

cjszybinski
11-01-2009, 06:57 PM
Im going to head to the dealer this week to see if this is still being covered by GM - though I replaced the air suspension with belltech equip.... we shall see

pgoodyear
11-09-2009, 02:33 PM
I thought I was going crazy feeling like I was being hit in the back when stopped at traffic lights. No i know i'm not alone. Funny my saab 9-7x is in the shop today getting this and other issues hopefully resolved. When I told them about the issue's with drive shaft yoke . They pretty much tlod me I was mistaken.Still under warranty thank god, but said 89.00 diagnos charge if my compalints where not warrantied. How do you like that?:bonk::bonk:

fj4072
11-09-2009, 05:30 PM
I have the same problem, but with an additional problem while driving at parking lot speed. My TB seems to jerk slightly back and forth while my foot is only feathering the accelerator to keep at a constant speed. This will also happen while traveling around 40mph and me just keeping a constant speed on flat road, the TB will jerk slightly bacj abd forth, I'm thinking driveline, but not sure. I don't have this problem at highway speeds at all. I mainly feel this at very low speeds, while in 2 wheel high. 02 4x4 TB 168k, had my tranny rebuilt about 40k ago. This feels like a driveline problem. Any suggestions?


Thanks

n0kfb
11-09-2009, 07:18 PM
I have the same problem, but with an additional problem while driving at parking lot speed. My TB seems to jerk slightly back and forth while my foot is only feathering the accelerator to keep at a constant speed. This will also happen while traveling around 40mph and me just keeping a constant speed on flat road, the TB will jerk slightly bacj abd forth, I'm thinking driveline, but not sure. I don't have this problem at highway speeds at all. I mainly feel this at very low speeds, while in 2 wheel high. 02 4x4 TB 168k, had my tranny rebuilt about 40k ago. This feels like a driveline problem. Any suggestions?


Thanks

I'm going to suggest you take a good close look at your tires. To me it sounds like you are describing radial tire 'waddle'. This happens when tires get old or damaged, and the belts no longer hold the tread straight and true.

-- Dan Meyer :coffee

:hijacked

fj4072
11-09-2009, 07:25 PM
I'm going to suggest you take a good close look at your tires. To me it sounds like you are describing radial tire 'waddle'. This happens when tires get old or damaged, and the belts no longer hold the tread straight and true.

-- Dan Meyer :coffee

:hijacked


Yeah, I'd agree with this, but, my tires are only 1yr old and have never been damaged, also weren't cheap tires.

n0kfb
11-10-2009, 12:24 AM
Yeah, I'd agree with this, but, my tires are only 1yr old and have never been damaged, also weren't cheap tires.

Don't discount anything without checking, and check the easy to check stuff first. Tires are easy to check.

-- Dan Meyer :coffee

:hijacked

fj4072
11-11-2009, 12:33 PM
Don't discount anything without checking, and check the easy to check stuff first. Tires are easy to check.

-- Dan Meyer :coffee

:hijacked


OK, I took it to a friends tire shop, they looked and told me the tires looked good. Had him roadtest it with me and said my problem feels like a rearend or a possible bad u-joint. What do you think?

the roadie
11-11-2009, 01:31 PM
I'm a big fan of simply greasing the slip yoke. It can take as little as ten minutes if you're used to dropping your driveshaft. This was my fix.

markarock
11-11-2009, 01:37 PM
Normally you can't tell if a tire has a bad belt, except in extreme circumstances where the belts have separated and there is a noticeable bulge in the tread area at one point.

Usually the tire looks completely normal, and it would take an x-ray to "see" the bad or shifted belt. I wouldn't rely on the fact that your tires "look" ok.

Further, expensive tires, new tires, and even new expensive tires that have never been damaged or abused can and do experience belt problems. Yes, you normally get what you pay for and so the likelihood is less with expensive tires, but it is still possible. If it can happen, it will!

So, how to really check for a tire problem? Easiest is to swap tires with a fellow TB/Envoy owner and see if the problem goes away. If it does, then you have demonstrated that the problem is with your tires, or at least one of them. Reinstall your tires one at a time until the problem returns. Bingo, you've identified the bad tire.

Alternatively, swap on your spare one corner at a time and take it for a test drive to see if anything changes. If you have two bad tires, this might not show you the problem, but that is highly unlikely.

fj4072
11-11-2009, 01:57 PM
Normally you can't tell if a tire has a bad belt, except in extreme circumstances where the belts have separated and there is a noticeable bulge in the tread area at one point.

Usually the tire looks completely normal, and it would take an x-ray to "see" the bad or shifted belt. I wouldn't rely on the fact that your tires "look" ok.

Further, expensive tires, new tires, and even new expensive tires that have never been damaged or abused can and do experience belt problems. Yes, you normally get what you pay for and so the likelihood is less with expensive tires, but it is still possible. If it can happen, it will!

So, how to really check for a tire problem? Easiest is to swap tires with a fellow TB/Envoy owner and see if the problem goes away. If it does, then you have demonstrated that the problem is with your tires, or at least one of them. Reinstall your tires one at a time until the problem returns. Bingo, you've identified the bad tire.

Alternatively, swap on your spare one corner at a time and take it for a test drive to see if anything changes. If you have two bad tires, this might not show you the problem, but that is highly unlikely.



Point well taken, I'll take it back to my buddy at the tire shop and try a different set including my 2nd set of tires that I have.

I will also be dropping my driveshaft this weekend and lubing the slip yoke. Needs to be done anyway to take care of the infamous "bump", might be my problem with the jerking also, we'll see.

Will let you know what the results are this weekend. :thx

MA Trailblazer
12-30-2009, 07:11 PM
My truck would do the bump but only after a hard stop and then just when you started moving again. I took out the driveshaft and greased the inside and outside of the slip yolk and that solved the problem. Before I greased it the bump would happen every few days. It has been over two months since I greased it and it has happened since then. :)

trisquit3
01-25-2010, 12:37 PM
Envoy Fan,
As I said, the bump happened while sitting still after a fairly hard stop. The yolk gets hung up and then breaks lose while sitting at a light. The first time it happened, I looked in the mirror expecting to see knuckles on a steering wheel behind me, yet noone was around but me.
The other thing I mentioned, the clunk, happens only when accelerating.
Took it into the dealer and they greased the yoke. Stays for about six months. Then starts up again.

Fairly new to the forum here but you guys helped alot when I changed out my fan clutch assembly (PITA). Anyway, I have had the same problem since I picked up my 2002 SLT Envoy with 75,000 on it. The "bump" comes and goes and usually happens after sitting all day at work. Once she gets warmed up it seems to go away. I have just over 100,000 on her now and haven't heard it in a while (knock on wood).

BVANMCKNIGHT
01-25-2010, 12:55 PM
I have never felt but I have had two friends feel this anomaly.

fj4072
02-22-2010, 06:35 PM
Point well taken, I'll take it back to my buddy at the tire shop and try a different set including my 2nd set of tires that I have.

I will also be dropping my driveshaft this weekend and lubing the slip yoke. Needs to be done anyway to take care of the infamous "bump", might be my problem with the jerking also, we'll see.

Will let you know what the results are this weekend. :thx



Took a while to find time to get this done, but it's done and solved. I dropped the drive shaft and greased the slip yoke. This not only solved the bump, but also solved my jerking back and forth while feathering the accelerator. The slip yoke was bone dry and I now see why I was having the problems. Thanks for the info and pictures Roadie!:thx

4x4forLIFE
02-22-2010, 06:42 PM
What kind of grease do you use for this problem? I only experience it when I first start my tb up in the morning, when it's sitll cold..

DJones
02-22-2010, 06:51 PM
I fixed this problem Friday. It was warm outside, comparatively speaking, and was tired of the bump. Took a hammer to the u-joint after removing the bolts because it was so rusty. After some yanking to get the shaft out, I loaded up the grease. I used Kendall Super Blu grease, however it is spelled.

its garrett
02-22-2010, 07:58 PM
good to know! i've had this issue only 2 or 3 times after coming to a stop, varying from 5 seconds to maybe 30 seconds.

fj4072
02-22-2010, 08:25 PM
good to know! i've had this issue only 2 or 3 times after coming to a stop, varying from 5 seconds to maybe 30 seconds.

Quick and easy fix. About 15 minutes worth for me (no rust). You'll be happy you did it.

fj4072
02-22-2010, 08:35 PM
No grease fittings. Just remove four bolts from the rear U-joint attachment, slide the driveshaft forward 1/2", drop it down at the back, pull out, and voila!

http://www.roadie.org/driveshaftding2.jpg

http://www.roadie.org/ds2.jpg

http://www.roadie.org/axle112.jpg


Hey Roadie, I'm very curious. I see in your photo what looks like grease spread out on the outside of the driveshaft near the pumpkin. What is the purpose of this? Might be a dumb question, but I had to ask. Thanks

the roadie
02-22-2010, 11:26 PM
Hey Roadie, I'm very curious. I see in your photo what looks like grease spread out on the outside of the driveshaft near the pumpkin. What is the purpose of this? Might be a dumb question, but I had to ask. ThanksNot dumb at all! It's the damage a large rock caused when I was trail riding on a side hill and accidentally slid sideways at the same time I was trying to go forward. Almost lost my driveshaft totally that day.What looks like grease is just rock rash. The spiral appearance is the forward travel for the last couple of inches as the rick pressed against the tube. I was extremely fortunate that day!

Documented:
http://forums.trailvoy.com/showthread.php?t=62870

fj4072
02-23-2010, 02:02 PM
Not dumb at all! It's the damage a large rock caused when I was trail riding on a side hill and accidentally slid sideways at the same time I was trying to go forward. Almost lost my driveshaft totally that day.What looks like grease is just rock rash. The spiral appearance is the forward travel for the last couple of inches as the rick pressed against the tube. I was extremely fortunate that day!

Documented:
http://forums.trailvoy.com/showthread.php?t=62870


Gotchya, thanks for the thread. My alum shaft would of been toast. At least you have a spare now, to get you off the trail next time. Thanks for the info on the split yoke, much more comfortable ride. I still have a cold one for you waiting her in N. CA.

Heavyblaze
02-23-2010, 07:42 PM
I heard of a GM technician using a racquetball in the slip yoke to help the yoke from sticking. I found it on another gm truck club forums.:undecided

1997harley
02-23-2010, 08:06 PM
I used disc brake caliper slide grease, nice and thick, good with heat and I get about 20K before having to grease it again. BTW, our truck has 3;73, open diff, no air suspension.

Uber
04-09-2010, 01:26 AM
I had the following repair done several months ago

Bulletin No: 07-04-17-001D

Date: May 18, 2009
TECHNICAL

Subject: EI07148 - Bump/Thump Heard/Felt from Driveline or Rear Suspension after Braking (Replace Output Shaft Yoke)

Models:
2004-2007 Buick Rainier
2004-2009 GMC Envoy,Envoy XL
2004-2005 GMC Envoy XUV
2002-2004 Oldsmobile Bravada
2005-2009 Saab 9-7X Models
with Automatic Level Control Rear Suspension (RPO G67)
_______________________________________________

This Bulletin is being revised to update the labor time for 4WD/AWD applications. Please discard Corporate Bulletin Number 07-04-001C (section 04 -- Driveline/Axle)
_______________________________________________

Condition:
Some customers may comment on a bump or thump noise heard from the rear suspension or felt in the floor. The information below will affect vehicles with G67 Automatic Level Control rear suspension. This noise will typically occur at traffic lights after rapid stops. This noise is due to a combination of the rear electronic suspension attempting to level the vehicle and the driveline becoming unbound after these rapid stops.

Correction:
Contact your DVM (District Service Manager) for approval prior to making any repairs. 4WD vehicles - Replace the Output Shaft of the Transfer Case and the Drive Shaft Yoke and grease with p/n 12345879 (in Canada use p/n 10953511). Reinstall and evaluate operation. 2WD Vehicles - replace the Output Shaft of the Transmission and Drive Shaft Yoke.Reinstall and evaluate operation.

Unpublished Labor guide:
F9721*
Rear Propsaft Output and Yoke Replace
4WD 4.2 hrs

it didn't work

it has been in the shop for the last 3 days.....

want to guess what they are telling me?

I nearly fell over laughing.... they were able to replicate the issue!!!.... but they have checked everything.... the air ride suspension is fine..... their guess is that it is.....(drum roll) a backfire!!....yes........they are serious!!! - all they can do is replace my plugs (not under warranty of course....)

:laugh:MORONS!!!!:duh:

I had to rush off to a meeting....but will follow up in the morning..... I cannot wait for them to explain how the vehicle backfires once a day at the same time ....only under the conditions that it is cold ...in Drive and stationary with the brake depressed for 15 seconds..... this is one conversation I want to record!!!! I am going to ask for it in writing....

Apparently they have phoned GM repeatedly and the Rear Propsaft Output and Yoke Replace is the only thing that GM will allow to be done under warranty to address the issue?

Looks like I will end up just having to live with it.... it is obvious to me that GM has no care whether they deal with this or not.... neither do the dealership.... they are busy as hell all the time because all the other local dealers closed down........ I had the 'voy in for 2 days last week and they actually did NOTHING because they didn't have time to look at it! They paid for a rental for me but I had to go out of my way and be late for work to drop it off. It has been in for 3 days this week and all they have done is change the oil!!! I honestly believe that GM is losing it's grip on reality. 5 days rental for an oil change and a comedy diagnostic?? Jeez! I am going to tell them to grease their own :yokes and take it to another dealer on the other side of town.

boosteddakota
05-25-2010, 10:22 PM
ok.....no air and i have the "thump" also. only mine comes with a twist. most people are saying this happens in drive when stopped. well mine does that too but it also does it every now and then after i put it in park. does that sound like the same sticky yolk problem also? i always thought it was the tranny down shifting into 1st gear until it did it in park. i hate this tranny anyway so i wasnt giving it any leeway

Tsquires
03-13-2011, 09:07 AM
After reading a number of replies I noticed that no one mentions a condition where the bump is felt numerous times at a single stop. At first I thought the sticky yoke problem was a reasonable answer but 2 things convinced me otherwise: 1) I've had the yoke lubricated by the dealer AND eventually replaced by the dealer, 2) I feel the bump sometimes 3 or 4 times in succession (I've never waited to see if it would continue beyond that). I suppose you could say that having the dealer work on it has actually made it worse.

Maybe my problem is different somehow but I'd like to know if anyone else is feeling the "bumped from behind" sensation more than one after coming to a stop. I'm concerned that I actually have a transmission problem and I'm nearing the end of my extened warranty.

sdadams
03-13-2011, 01:28 PM
Went away after dealer changed yoke, but prior to that would bump multiple times on occasion.

asimmons136
05-12-2011, 04:58 PM
Went to the dealership and they applied a special "high pressure" grease that the tech said they are disallowed from using in any other application to the yoke. This has solved my problem, but I am just waiting for it to come back. They wont change out the yoke unless the grease doesnt do the job.

Ralph_T
05-13-2011, 03:16 AM
The bump from behind feeling comes and goes for me. I always thought it was a vibration issue but now that I think about it a "bump from the rear" sounds like more of an accurate description. But I think the bump is always there in some mild form or another if I really concentrate on it. This happens to me when at a stop and just as I lift my foot off the brake. I am being told on the forums by different members that it could be the tranny or engine mounts as well. Now I am really confused and I don't want to be throwing $200 for prop and tail shaft + another $175 for tranny and engine mounts to see if replacing any one of them "fixes" the problem.

Envoy4Life
05-13-2011, 04:30 AM
Air Suspension

Ralph_T
05-13-2011, 04:52 AM
Air Suspension

I don't have air suspension. I have coils

mwfaith1971
05-13-2011, 08:11 AM
Ralph,

Try the easy things first. Grease the slip yoke and see what happens. I'm almost positive that you'll find the problem disappears.

Matt

Ralph_T
05-13-2011, 09:21 AM
Ralph,

Try the easy things first. Grease the slip yoke and see what happens. I'm almost positive that you'll find the problem disappears.

Matt

I know... Put the rear axle up on jack stands (which I can't do because of the darn sway bar), block the front wheels and then put it in neutral and then disconnect the battery. Should be a piece of cake if I wasn't so gosh darn claustraphobic under there. I hope the driveshaft isn't frozen.:(

Cyrix2k
05-19-2011, 07:32 PM
I'm glad I found this thread. My parents' '04 Rainier with 77k miles does this and it's driving me nuts. They're the kind of people that are happy if the car moves so I doubt they care. Is there any possibility of long term damage if this isn't addressed?

CLEAR
09-16-2012, 09:47 PM
I have the same problem. Mine will clunk sitting in park in the driveway while the compressor is airing up the bags.

sdadams
09-16-2012, 10:39 PM
GM replace my driveshaft at 36K miles in an '06 Envoy Denali. They said the tolerance between the splined output shaft of the transmission, and the female mating end of the driveshaft were too tight, causing binding. The "Bump" was felt when the two pieces would finally slip. New drive shaft solved the problem.

CLEAR
09-19-2012, 06:57 PM
took the driveshaft out. It looked good slipyoke had oil on it, no rust. I greased it real good but it still clunks. Its real bad just sitting in park when the airbags are filling. Anyone ditched airbags for coils?

CLEAR
10-11-2012, 10:02 PM
still looking to fix it. Driving me crazy. Clunks several times when stopped.

sBoddie
10-12-2012, 10:52 AM
Used to happen all the time. Got much worse right before our tranny got toasted under warranty. When it started up again a couple of years ago I ask my mechanic about it who has has a couple of Suburbans. He said if you're driving in traffic at lower speeds try to keep it in "3". I think the tranny has trouble sometimes jumping down from overdrive at a stop.

We have especially noticed it when we have a hard stop from 55+. In that case I shift it down to 3 when I decide to hit the brakes. We haven't been feeling it since.

denaliguy
11-08-2012, 04:05 PM
Great posts on this thread. I too have the bump on my '07 Envoy Denali. Only happens once in while, not every time, after I come to a complete stop. Only bumps once, some more noticeable than others. The harder I come to a stop the more likely it'll happen. Anyway, I am picking up some Kendall Super Blu grease this weekend and will be dropping my driveshaft to grease the slip yoke next weekend. I'll let you know how it turns out after a week of driving. Wish me luck and thanks to those who have offered suggestions/success stories.

SlapChuck
12-09-2012, 12:06 PM
I have been dealing with this problem on my 07 tbss for a couple months. Started after dealership replaced trans and rear end under warranty. First fix was a new nickel plated upgraded slip yoke that was supposed to be a fix for this common issue. Since that didnt work I'm thinking they either didnt use grease, or the problem is with the new transmission's output shaft. truck is going back to dealership in two days, ill report back.

denaliguy
12-11-2012, 12:51 AM
Well I greased the slip yoke about 3 weeks ago and I'm still getting the bump. The slip yoke was pretty dry when I opened it up, greased it nice and thick and it didn't take care of it. I do have an extended warranty on it, but I was trying to avoid paying the deductible. Looks like I don't have a choice. I'll reply back once I'm able to take it in and hopefully get it fixed.

VelociJuris
01-29-2013, 05:34 AM
If the grease that is used wears out quickly perhaps a moly paste would be helpful. http://www.henkelna.com/cps/rde/xchg/henkel_us/hs.xsl/product-search-1554.htm?nodeid=8797877698561

denaliguy
03-04-2013, 04:45 PM
SlapChuck, were you able to resolve this? Would love to hear a success story.

I have been dealing with this problem on my 07 tbss for a couple months. Started after dealership replaced trans and rear end under warranty. First fix was a new nickel plated upgraded slip yoke that was supposed to be a fix for this common issue. Since that didnt work I'm thinking they either didnt use grease, or the problem is with the new transmission's output shaft. truck is going back to dealership in two days, ill report back.

nick_wa
03-05-2013, 01:17 PM
Greased mine when i did u joints and no more bump.

denaliguy
03-05-2013, 02:53 PM
What kind of grease did you use?

Greased mine when i did u joints and no more bump.

dporter
03-05-2013, 04:25 PM
My 07 Denali has done the bump thing since new. Only after a hard stop and sometimes there is a delay after being stopped. I always thought it had something to do with the suspension leveling with the brakes locked. I don,t know if the rear wheels need slight rotation when the suspension lowers but maybe if the suspension tries to lower when the wheels are locked it hangs until enough weight is transferred causing a bump when it does lower. I have had drive shaft front yoke slap on my old Blazer and it was more of metallic clang and no noticeable sensation of being bumped. I just turned 120K miles on this car with original brakes so you know I don't do a lot of hard stops.
Dave:)

purduestuddk
04-06-2013, 09:39 PM
This happened to me a couple of times also, but I noticed it only happened when the AC compressor was running.....figured out I had a refridgerant leak and it was causing my AC compressor to cycle on and off.

Jewel red 5
04-07-2013, 02:24 AM
Had mine slip yok replaced last year by dealer they said there's a slight redesign in the new one to get ride of the bump feeling. So far since they installed it its gone for more then a year now used to do it all the time. Good luck to you all.

Ryda55555
04-07-2013, 02:47 AM
When im about to come to a harder stop i get a downshift jerk which i think is normal cause i feel like the braking is restricting the movement of the truck while in 2nd gear so because of the 4 gears and a lot of torque it gives it a slight jerk when shifting into first with too much brake involved

opiefavors
04-15-2013, 07:57 PM
Just bought my wife a 2002 tb. It does the jerck while stopping. I put it in Neutral while stopping and it dosnt do it... my 2cents.

03ChevTB
07-04-2013, 07:24 PM
I traded up from 03 TB to an 06 Saab 9-7x about 2 years ago. I never had the bump when I owned the TB but had it with the Saab right from the get go. I tried getting the driveshaft replaced under (aftermarket) warranty...that was a no go. I took it into a Quick Lube place and they upsold me a bunch of fluid changes including the rear diff fluid. Low and behold no more bump...almost 2 years later. So before you go spending money on replacing shafts, change the fluids first.

denaliguy
10-10-2013, 03:22 PM
A couple people in here posted that they changed out some fluids and it went away. I believe changing the rear differential fluid is what's fixing the problem. I did my front and rear at the same time and the bump went away completely. It's an insanely easy job to do yourself and the only cost you'll have is for the fluid. I used 75w-90 full synthetic gear oil (about $11 per bottle). It took about 2 1/2 to 3 bottles for each differential so you're looking at $50-$60 to do it yourself (using the top end oil).

I have tried to simulate the bump and it won't do it at all. It's been 2 months since I replaced the differential fluids. Such a relief...