4WD question for you.

[wookiee2cu]

Sorry, I'm a total noob and this is my first rig with 4wd. I have a 2002 Trailblazer LTZ with about 39,350 miles. My question is this. Today it started snowing and cars were sliding all over the place so I put my rig into 4hi (dead stop with transmission in neutral). Everything was great, no sliding nothing. Anyways, I pull into my apartment complex and went to back into my parking spot. I slowed down to a crawl and started cranking the wheel to get into a good position before I came to a complete stop to put it in reverse to back into my spot. When doing this there was a rubbing/knocking vibration. Should I be worried or is this normal as I was doing a tight turn in 4hi at a slow speed? I figured it wasn't a good idea to come to a complete stop then crank the wheel but I didn't expect this when I was still at a crawl. I would phone my buddie whose familiar with my righ but wouldn't you know it, my cell phone reads "Network Busy" everytime I try to place a call. I'm in Seattle and eveyone here is freaking out and calling their mother I guess. People here do NOT know how to drive in the snow. It took 1 hour and 10 minutes to go 1.6 miles. Anyways I was just curious if this vibration is normal at low speeds in 4hi while cranking the wheel to make a sharp turn. Thanks in advance for any input you may have!

[low87b2200]

wheels locked together (locker) no worries nothing is a matter i dont understand the rubbing though.... mine while in 4hi if i turn on black top it will hop wheels locked together causeing a vibration kind of ...... other then that no worries i dont really now if thats what your problem is ....rubbing i cant think of anyhting besides it rubbing on the wheel well

[wookiee2cu]

low87b2200, thanks for the quick response. The vibration was in the steering wheel while my hands were on it (I should have explaned that better in the original post). Your description of the "wheels hopping" is accurate to what I experienced. Thanks for the info., was dreading the possibility of having to take my rig into the dealership for an inspection! Thanks again!

[low87b2200]

the vibration in the stering wheel .... i cant think of anything right off the top of my head..... but i really wouldnt worry to much i may have just be the tires hopping and sliding if the ground was slick ... dont know

[Blazernut]

Sorry, I'm a total noob and this is my first rig with 4wd. I have a 2002 Trailblazer LTZ with about 39,350 miles. My question is this. Today it started snowing and cars were sliding all over the place so I put my rig into 4hi (dead stop with transmission in neutral). Everything was great, no sliding nothing. Anyways, I pull into my apartment complex and went to back into my parking spot. I slowed down to a crawl and started cranking the wheel to get into a good position before I came to a complete stop to put it in reverse to back into my spot. When doing this there was a rubbing/knocking vibration. Should I be worried or is this normal as I was doing a tight turn in 4hi at a slow speed? I figured it wasn't a good idea to come to a complete stop then crank the wheel but I didn't expect this when I was still at a crawl. I would phone my buddie whose familiar with my righ but wouldn't you know it, my cell phone reads "Network Busy" everytime I try to place a call. I'm in Seattle and eveyone here is freaking out and calling their mother I guess. People here do NOT know how to drive in the snow. It took 1 hour and 10 minutes to go 1.6 miles. Anyways I was just curious if this vibration is normal at low speeds in 4hi while cranking the wheel to make a sharp turn. Thanks in advance for any input you may have!

Your 4WD is fully selectable while moving EXEPT 4LOW. That is the only time you must stop and put it in neutral. When you hit a lot of just wet pavement use AWD.

Remember that 4WD still can't stop and the 4700 lb truck really likes to slide. Sometimes the anti lock brakes are a PITA.

4low is great for climbing steep hills slowly and getting down the same in a controlled fashion.

I just got back from the snow covered rat race and saw a lot of people that lost he battle.

Cheers,
B.

[DucatiSS]

My older Silverado does the same thing. I asked my mechanic and he said it's normal with chevys. :confused:

[the roadie]

Should I be worried or is this normal as I was doing a tight turn in 4hi at a slow speed? I analyzed the problem last year because we don't actually have a very tight lock in the transfer case, but the torque transfer is very high. At low speed on dry pavement, even if you have the G80 automatic locking rear differential, you haven't gotten up to the RPM difference that's going to activate it.

So where does wheel hop come from? It's NOT left to right locking as some folks guessed. We have no front locker or limited slip, and the G80 can't activate at such low speeds.

The front driveshaft is going to turn at the average of the left and right front wheel RPMs. (The open front differential just adds the RPM together and divides by two, so it's the average.) Same thing in the rear. BUT, the front and rear drive shafts want to turn at different rates because the turning point is in line with the rear axle, and FARTHER away from the front. Since the transfer case tries its best to keep the front and back driveshafts turning at the same rate, wheel hop to relieve drivetrain stress is the result. It's worse in the trailvoys than most other vehicles because of our EXTREMELY tight turning radius, one of the things the designers got right.

See this scale drawing of a short wheelbase vehicle to see the math. It's not going to break anything right away, but it's not good to let so much stress build up. Front CV joints are probably the weakest link, and are worth protecting by going back to A4WD or 2WD whenever you're on pavement that doesn't slip easily.

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

[ghoster]

Ouch.....Roadie.....quit making me think...now I have a headache!

[tb05]

See this scale drawing of a short wheelbase vehicle to see the math. It's not going to break anything right away, but it's not good to let so much stress build up. Front CV joints are probably the weakest link, and are worth protecting by going back to A4WD or 2WD whenever you're on pavement that doesn't slip easily.

http://www.roadie.org/envoyturning.jpg
:thumbsup:
Hey Roadie, I saw that on your web, and I, ahem, "borrowed" it to show a buddy of mine what he is doing to get the "wheel hop". He didn't understand that it was possible for the front and rear, right and left wheels to travel different distances. Great drawing! Thanks!:thx

[wookiee2cu]

low87b2200, I think the vibration I felt was just the wheels hopping. It didn't rattle my teeth or anything but I could feel it a little bit. The pavement was not bare, had a good dusing on it, maybe about 1/4" or slightly less.

Blazernut, I was in 4hi, I actually had the brains to look in the owners manual before doing anything (rarely the case with me :) ). Even though I was using the 4wd I still drove like a grandma, it's always the people who get over confident who end up in the ditch and I didn't want to join them.

the roadie, thanks for the explanation, it makes sense a little better now.

Thanks guys, I knew this was the place to come to!

[ghoster]

Even though I was using the 4wd I still drove like a grandma, it's always the people who get over confident who end up in the ditch and I didn't want to join them.



Its better to be cautious. I have seen alot of people in the ditch....they seem to forget that 4 wheels slide on ice just as easily as 2. :cool:

[the roadie]

Ouch.....Roadie.....quit making me think...now I have a headache!Math is your friend. If you're an engineer. :D

:thumbsup:
Hey Roadie, I saw that on your web, and I, ahem, "borrowed" it to show a buddy of mine what he is doing to get the "wheel hop". He didn't understand that it was possible for the front and rear, right and left wheels to travel different distances. Great drawing! Thanks!:thx Thanks for the kind words. I got obsessed with the issue and couldn't let it drop once I experienced it myself and somebody claimed it had to be because we have a front locker, which I knew we didn't. The steering linkage has to be carefully designed because the left and right wheels end up at different angles at full lock! But that's an issue of scrub, not wheel hop.

[tb05]

True, it is scrub, but for some newer off roaders, they tend to live in the Petersens world of off-roading and until they actually have some experience playing and breaking things, you lead 'em along and they learn as they go. Explaing that what it really is the driveline binding since there is no separation of the speed of the front and rear axles and it sloughs off excess on the shorter distance line is hard , unless of course you find Roadies diagrams! :)

[the roadie]

....since there is no separation of the speed of the front and rear axles...I was sure pleased to discover that the clutch plates in the transfer case, when commanded to go to max torque transfer by the encoder motor in 4HI or 4LO, actually coupled the front and rear together well enough to cause scrub on dry pavement. That meant that even though we have an open front diff (until ARB comes out with a locker for the H3's and we can adopt it), a front tire spinning in the air won't halt all forward progress as long as your rear locks up with the G80. It isn't as great as a full-locking transfer case, but it's way better than the slipping you get on purpose in full-time AWD mode. You can see a bit of front wheel spin in the videos I posted of Teebes and me last weekend. http://forums.trailvoy.com/showthread.php?t=18986

There are a bunch of us just waiting for ARB at this point to throw the Hummer H3 crowd a bone, and then we'll pounce.

Also looking for a transfer case expert to tell us if we can swap a gear or two and go to 4-to-1 instead of 2.3-to-1 for the LO ratio.

[teebes]

There are a bunch of us just waiting for ARB at this point to throw the Hummer H3 crowd a bone, and then we'll pounce.

Also looking for a transfer case expert to tell us if we can swap a gear or two and go to 4-to-1 instead of 2.3-to-1 for the LO ratio.

:yes:

[MichEnvoyBoy]

My older Silverado does the same thing. I asked my mechanic and he said it's normal with chevys. :confused:

Actually I think my Fathers 96 Dodge Ram 4x4 is ALOT worse than my Envoy with binding while in 4wd. The Dodge literally "hops" while trying to turn locked in 4wd :eek: Its slightly disturbing. All I get in my Envoy is vibration/noise/resistance to move forward.

[the roadie]

Actually I think my Fathers 96 Dodge Ram 4x4 is ALOT worse than my Envoy with binding while in 4wd. The Dodge literally "hops" while trying to turn locked in 4wd :eek: I suspect this is because our transfer case isn't fully locked up. The encoder motor commands the clutch pack to full engagement, with maximum torque transfer, but it's not a true locking transfer case (says the factory shop manual). Someday, I have to try this on dry pavement with EFILive running, which can tell me the RPM of the both output shafts of the transfer case, to confirm there's some transfer case slippage. I expect there isn't much, but some.

[mudd_magnet]

those vids are awsome makes me feel better abought the envoy and it's tuoughness

here is a thought for you guy's since you are wanting to change out the gears in the t-case anyways why not just swap in a old np-203 or np-205 out of a older half ton if the envoy is drivers side output the 205 out of a ford has the drivers side output or is it gm I forget but I know the ford and gm are driver and passenger side out put just forget which lol It would probably be cheaper to do it that way and you would be able to get rid of the electronic transfer case control I am sure advanced adapters would be able to make something up if the two are a different

[the roadie]

those vids are awsome makes me feel better abought the envoy and it's tuoughness Thx. More coming tonight from a solo trip I just got back from. Monitor the Pics and Videos forum.

here is a thought for you guy's...why not just swap in a old np-203 or np-205...I am sure advanced adapters would be able to make something up if the two are a differentThat's actually a HOOT of a great idea! We don't need the silly A4WD mode anyway. Can you imagine a vehicle with a floor-mounted automatic shifter, with twin stick transfer case controls coming out of the side of the console? :D

Actually, there is one tremendous advantage of new twin-stick controls - you can disconnect the front output, and put the rear into 2WD LO. A previously unavailable mode that can be useful in certain conditions.

http://coloradok5.com/jkwtwinstick/jkwmain.jpg

[topprolmc]

Also looking for a transfer case expert to tell us if we can swap a gear or two and go to 4-to-1 instead of 2.3-to-1 for the LO ratio.

Not an expert, but due to researching a TC issue for a friend, I have found out a few things...
Most fullsize GM trucks only have 2.X:1 TC's....

I also found that the colorado/Canyon share 80% of it's parts with the TB.

[MTPockets]

..it's not a true locking transfer case (says the factory shop manual). Someday, I have to try this on dry pavement with EFILive running, which can tell me the RPM of the both output shafts of the transfer case, to confirm there's some transfer case slippage. I expect there isn't much, but some.

I know whacha mean. From the feel of them, they are either slam full on, or full off. This is why I hate running A4wd. I cant stand that slamming jolt of the front drivetrain kicking in.:mad: Maybe they will slip under severe load, but that doesn't feel like the case either with 4hi on a no slip surface.:eek:

Joel