4 wheel drive [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: 4 wheel drive


Aerostud1026
10-24-2006, 12:25 PM
Hey guys,

today I went out and tested the 4 wheel drive seeing how since Ive had the truck ive never really tested it out.......so I took it out and it works great....one of the things I did was to recognize its working is turning tight at low speeds in a circle and if the car bucks or hesistates its working.....well in mid circle I was satisfied with the results so I threw her in park and flipped the switch....back to 2 Hi before straightening the wheel....after I did I felt a "thump" sort of speak.....so I straightend the wheel and threw her back in 4 Hi...and tried again to make sure I didnt mess anything up....it still works....but I was concerned with the "thump" I felt.....did I do anything wrong? I know the manual says we can switch on the fly but my uncle said he had a vehicle that was supposed to do that and he messed his 4 wheel drive up doing that, so he told me he always comes to a stop before switching...but never said to throw it in park... Im a newbie to 4 wheel drive vehicles as my previous cars were mostly sports cars...thanks alot

HOTRODSURFER
10-24-2006, 12:41 PM
You May Be Feeling Transfer Case Shifting Back Into 2 Wheel Drive-

Aerostud1026
10-24-2006, 12:47 PM
Thats probably what it was.......because it happened when I flipped the switch back....I guess the position of the car and everything else was the reason I felt it.....I havent felt it again and I took it out about 3 times today.

Frostee
10-24-2006, 01:00 PM
....back to 2 Hi before straightening the wheel....after I did I felt a "thump" sort of speak.....so I straightend the wheel and threw her back in 4 Hi...

my guess would be because you had the wheels turned and you were stopped. the gears letting go is probably what you felt, which probably just reduced the pressure on your front drive axle.

it was probably nothing to worry about at all.

iDontKnow
10-24-2006, 04:03 PM
It's the tires binding. You shouldn't use 4HI/4LO on dry pavement. The thump was the transfer case releasing and the tires unbinding.

Reference thread: http://forums.trailvoy.com/showthread.php?t=6710

josh_4184
10-24-2006, 05:07 PM
My Dads 2002 F150 4x4 always made some sort of thump when switching into 4x4. It did this from day one from the dealer. No matter if it was on comcrete,dirt,snow, it made the noise. It was also known to stay stuck in 4 low very easily. I havent tried the 4x4 in my TB. Hopefully it will work a little better that my dads ford.

Rob
10-24-2006, 05:54 PM
It's also a good idea to exercise the four wheel drive occasionally. At least a few times a year, just to make sure the various parts are lubed and the electronic parts are working properly. Any time I'm off pavement I switch to 4Hi and 4Lo if only for a few minutes.

RayVoy
10-24-2006, 06:01 PM
Frostee has it right, Ive had a number of GM 4x4s. Turning on a dry hard surface places a lot of pressure on the drivetrain. The wheels are locked (so to speak) and the turning circle is different for each wheel. When you switch back to 2 hi, the pressure is released, giving you the bang/thump. Hey, have you ever parked on a hill w/o the parking brake, letting the park dog hold the vehicle. Pulling the trans out of park gives a similar thump.

As I said, Ive had a number of these trucks, I drive them for 250 to 300k, 12 months of the year. They are in and out of 4 wheel drive when the weather is bad, They can and will go into 4 hi anytine between 0 and 50 mph (as long as the rears are not spinning). I have broken a lot of things on these trucks, but never a transfer case or a transmission. They are tough and they like to be shifted on the fly.

titanium10k
10-24-2006, 10:18 PM
so on the trailblazers when in two wheel drive does the front drive shaft spin? Does the front diff spin? I hear people say they put it in 4 wheel drive before they do a diff fluid change to warm up the fluid which makes me think the front is not spinning??? Does this mean that if the front doesnt spin that there are electric hubs on the trailblazer?:undecided :crazy:

RayVoy
10-25-2006, 06:52 PM
so on the trailblazers when in two wheel drive does the front drive shaft spin? Does the front diff spin? I hear people say they put it in 4 wheel drive before they do a diff fluid change to warm up the fluid which makes me think the front is not spinning??? Does this mean that if the front doesnt spin that there are electric hubs on the trailblazer?:undecided :crazy:

In 2 drive, the front driveshaft does not turn. The 2 halfshafts (from frt diff to wheels will turn with the wheel, but the halfshafts spin free in the diff. There is an actuator (in the old S10s it was vacuum operated) that connectes the diff and the halfshafts when transfer case is in 4x4.

the roadie
10-25-2006, 09:00 PM
...and the turning circle is different for each wheel.I went to the trouble of doing a scale drawing for another thread a while ago with the numbers for this effect, since if the transfer case didn't transfer a lot of torque front to back (in other words, if it slipped a lot) you would not bind up on hard pavement in tight turns. The scrubbing effect comes from the different turning radius of the front diff compared to the rear diff, and not from any sort of G80 locking effect within the rear diff as some had guessed.

For reference, here it is (SWB, not weiner-dog EXTs) :p

http://www.roadie.org/images/EnvoyTurning.jpg

Blueblazed
10-25-2006, 11:55 PM
For reference, here it is (SWB, not weiner-dog EXTs) :p



Careful with those "weiner-dog" EXT comments my friend! :D
I happen to like my EXT. Good drawing by the way!

the roadie
10-26-2006, 12:25 AM
Careful with those "weiner-dog" EXT comments my friend! :D :p :p That usually gets a reaction out of FattyTBEXT.

I happen to like my EXT. Good drawing by the way!I usually have to whack out a Visio drawing or two a day for some training need or another. Sometimes trailvoy needs training more than my :sleepy: customers.

Blueblazed
10-26-2006, 12:40 AM
:p :p That usually gets a reaction out of FattyTBEXT.
:laugh: I see! Maybe I just beat him to the punch! :)

I usually have to whack out a Visio drawing or two a day for some training need or another. Sometimes trailvoy needs training more than my :sleepy: customers.
:yes:
I hear you. But this is a good example of a picture (or a drawing) being worth a thousand words!

MTPockets
10-26-2006, 05:45 AM
..There is an actuator (in the old S10s it was vacuum operated) that connectes the diff and the halfshafts when transfer case is in 4x4.

Yep, the front axle disconnect on trail-voys is integrated into that bearing carrier on the inner right half shaft. See this eBay listing, the front axle disconnect motor (black box) can be seen to the far left, center. It basically splines/unsplines the right side for 4x4 or 2wd. http://cgi.ebay.com/ebaymotors/05-TRAILBLAZER-CARRIER-ASSEMBLY-DIFFERENTIAL-1061_W0QQcmdZViewItemQQcategoryZ33731QQihZ004QQite mZ140001061671QQrdZ1QQsspagenameZWD1V#ebayphotohos ting

G/luck
Joel

titanium10k
10-26-2006, 08:15 PM
Yep, the front axle disconnect on trail-voys is integrated into that bearing carrier on the inner right half shaft. See this eBay listing, the front axle disconnect motor (black box) can be seen to the far left, center. It basically splines/unsplines the right side for 4x4 or 2wd. http://cgi.ebay.com/ebaymotors/05-TRAILBLAZER-CARRIER-ASSEMBLY-DIFFERENTIAL-1061_W0QQcmdZViewItemQQcategoryZ33731QQihZ004QQite mZ140001061671QQrdZ1QQsspagenameZWD1V#ebayphotohos ting

G/luck
Joel

so is there one of these boxes on the left side also?

the roadie
10-26-2006, 08:54 PM
so is there one of these boxes on the left side also?From what I remember of the service manual cutaway drawing, there is only one disconnect solenoid and it manages to act on both side shafts. It's contained in the larger housing with the gears. I could scan the cutaway later, since I can't find one on-line.

Smoothbassman
10-26-2006, 09:11 PM
Yeah, man that thump was the transfer case unlocking. You should always throw it in neutral or park before shifting into 4 wheel high or low, and never on dry pavement. Once here and there not a big deal but over time you will tear something up.

MTPockets
10-26-2006, 09:16 PM
so is there one of these boxes on the left side also?

No, it's only needed on one side with an open style diff. By disconnecting one axle (in this case it's a half shaft) from a drive wheel, there will be no solid through-put on an open diff. As an example, on a FWD or RWD car, if you lift one drive wheel off the ground, you will be able to rotate the lifted wheel even though the vehicle is in park. Try to rotate both simultaneously in the same direction and no go. Same concept with a front axle disconnect.

Joel

Aerostud1026
10-28-2006, 09:48 PM
Hey guys,

Just for a piece of mind, How long would you need to drive your TB in 4WD on concerete making tight turns and all to ruin the 4WD or tranny? Again this is just for a piece of mind...Thanks

RayVoy
10-29-2006, 10:42 AM
Hey guys,

Just for a piece of mind, How long would you need to drive your TB in 4WD on concerete making tight turns and all to ruin the 4WD or tranny? Again this is just for a piece of mind...Thanks

Wow, now that would be a test. How long could you do that, I don't know!!!!! Probably for awhile (hours/minutes not days). Tires and condition of concrete surface would pay a part. Question is what would be likely to break -- what is the weakest link. I would quess the tranny would be ok, the multiplication of the diff gears would would cause a lot of strain in that area. Worn U joints and/CV joints could pop, wear on a 1/2 half spline could cause a shaft to spin. And, there are 2 tranfer cases. The AWD, with a clutch might be stronger, as there is no chance for slipage in the 2hi/4hi box. I am thinking a gear tooth or a joint is the most likely to fail. Let me know how the test goes haha.

clr114
10-29-2006, 09:57 PM
I understand the shifting into 4wd hi/lo and stuff, but whats the deal with the A4WD setting? My knob has 2hi, A4WD, 4hi, 4lo. I understand a4wd to be 2wd unless traction is needed, such as in puddles or whatever. Am I wrong? I'm rather new to the selectable 4wd thing. Can you drive in A4wd normal driving? :confused:

ghoster
10-29-2006, 10:08 PM
I understand the shifting into 4wd hi/lo and stuff, but whats the deal with the A4WD setting? My knob has 2hi, A4WD, 4hi, 4lo. I understand a4wd to be 2wd unless traction is needed, such as in puddles or whatever. Am I wrong? I'm rather new to the selectable 4wd thing. Can you drive in A4wd normal driving? :confused:


Its Automatic 4wd. The vehicle gets to pick when it thinks you need 4wd. Which is usually going to be when you experience wheel slippage. You CAN drive in a4wd all the time if you want. Alot of people choose to use 2 hi because they feel the A4wd doesn't always make the best decisions. Its whatever you prefer. If its my wife driving, I tell her to leave it in A4wd, if its me, I prefer to do it myself.....:cool:

clr114
10-29-2006, 10:15 PM
Thanks. I tried it the other dayfor a few miles, just making sure I didn't mess anything up. I had a jeep GC a few years ago with AWD and it was awesome in the rain. I hope the TB is just as good (just got it 3 weeks ago)

ghoster
10-29-2006, 10:16 PM
Thanks. I tried it the other dayfor a few miles, just making sure I didn't mess anything up. I had a jeep GC a few years ago with AWD and it was awesome in the rain. I hope the TB is just as good (just got it 3 weeks ago)


lol...in all honesty...my 2wd is good in the rain.:cool:

Aerostud1026
10-30-2006, 12:34 AM
Also again for a peace of mind.....


The "Service 4WD" light....does that usually let you know if somethings wrong down there in most situations?.....im sure there are some situations thats somethings wrong but no light comes on....but all in all.....if theres something wrong and you may not pick up on it.....will that light be handy enough to tell you in most cases?

ScarabEpic22
10-30-2006, 01:13 AM
I drive in A4WD only when I know there is a chance of wheel slippage (ie wet pavement and Im launching hard) or driving 70+mph up the pass when it is about freezing out and has rained earlier. A4WD is ok for use at all mph, whereas 4HI is good to 55 and 4LO really shouldnt be used past ~25-35mph. Automatic 4 Wheel Drive is basically "slip-sensing", if the rear wheels slip power will be transmitted to the front wheels removing the slip. It is the same mode the Bravy and Raniers are in fulltime as they are "AWD", but not true AWD like the SS is.

the roadie
10-31-2006, 04:51 PM
The AWD, with a clutch might be stronger, as there is no chance for slipage in the 2hi/4hi box.The service manual goes into some detail on the internals of the transfer case. There is no hard lock between front and back in 4HI or 4LO. The clutch pack is just commanded by the encoder motor to go to a maximum torque transfer pressure. But I believe it isn't infinite torque transfer - it can slip. But the tires tend to slip first, even on asphalt. In AWD, the clutch pack is commanded to go to a "close, but not engaged" position to save time when the computer senses wheel slippage. Then the clutch can move into a position that transfers torque a lot faster than when it was in the 2WD, fully-disengaged, position. In 2WD, the front differential is also disengaged and the driveshaft to it isn't spinning.

jwstewar
11-01-2006, 01:21 PM
Yeah, man that thump was the transfer case unlocking. You should always throw it in neutral or park before shifting into 4 wheel high or low, and never on dry pavement. Once here and there not a big deal but over time you will tear something up.

This is not needed on the Trailblazer (or their pickups for that matter). You can shift between 2wd/awd/4hi at speed - as long as the back tires aren't spinning. If you read you owner's manual they actually want you moving a little bit when going to/from high range to/from low range. They want you moving <3 MPH with the transmission in neutral. I've driven/worked GM 4wd trucks hard for a bunch of years and have yet to have a problem with any of them. I have a post some where on here about using my TB to try to pull my tractor out of the ditch when I got it stuck. I have low-range and I'm not afraid to use it.:D Though I don't use it as hard in the TB as I do the Silverado!:eek: