Snow and 4hi issue... 07 Envoy Denali

[mkalbarc]

The roads were a little bad this morning on my way to work so I switched it to 4hi. When I got to the parking structure I noticed on the way to the roof during every turn the truck would hesitate to go/lurch almost like I was trying to push something and it didn't want to go. It was very noticeable. For the last turn I switched to Auto and the problem was not there. Anyone have any ideas?

Also, not sure if this is related but ever since I bought the truck earlier this year it seems to be having a brake issue or trans issue. When stopped at a red light if I let off of the break slightly the truck will shake forward. It even shakes after the break pedal is completely disengaged (sometimes). It's not bad, but sometimes it's very noticeable.

Thank you

[pogbobo]

thats because in 4wd the wheels are forced/locked to turn at the same speed, so if you are not on a loose surface like sand, dirt or heavy snow they dont have the freedom to spin right when you turn ... when you turn on dry pavement in 4wd the left and right tires aren't spinning at the same speed and because they are locked they hesitate and lurch ... freaked me out the first time too ... when you are in auto-4wd and it doesn't do that on dry pavement its because it hasn't switched to full 4wd yet ... i think thats right for the most part ... i could be mistaken, i often am rofl ...

as far as the brake thing i dont know ... but i would take it in to get looked up, but hopefully someone will post with a better answer :)

[TrailBlazer LS]

Welcome to the site!! If your on slick and dry pavement then use A4WD not 4HI. 4HI will bind when turning in the dry and it's hard on the front diff. and transfer case. I hardly ever use 4HI, A4WD works the best for me in the snow and ice. I don't know about your other problem, I'm sure someone will chime in who does. Good luck!

Mark.

[JFSebastian]

Leaving it in 4HI on dry pavement will wear out the system faster and can possibly break it. I only use 4HI if stuck or if I can't see pavement (I'm off road or a few inches of snow). That goes for any vehicle, not just the Trailvoys.

[K2JJB]

thats because in 4wd the wheels are forced/locked to turn at the same speed, so if you are not on a loose surface like sand, dirt or heavy snow they dont have the freedom to spin right when you turn ... when you turn on dry pavement in 4wd the left and right tires aren't spinning at the same speed and because they are locked they hesitate and lurch ... freaked me out the first time too ... when you are in auto-4wd and it doesn't do that on dry pavement its because it hasn't switched to full 4wd yet ... i think thats right for the most part ... i could be mistaken, i often am rofl ...
:iagree:
The lurching is your drivetrain binding up as the tires do not have enough slip to releave the pressure of the gears in the transfer case (there is no center differential). Eventually it does finally slip and that is the lurch. But that is not good for the drivetrain components at all.

As others have said... 4HI only when you have low traction conditions (snow cover/ice/etc)... otherwise 4Auto is the way to go (transfer case is not engaged until the vehicle detects slip - and once it does not need it it releases)

[mkalbarc]

Thanks all for this info! I am relieved that this isn't ANOTHER issue. I've had a few with this vehicle so I guess I am just expecting more. If anyone else has any thoughts on the 2nd thing please let me know.
Thanks again!

:thx

[Pepper]

Hello, I think everybone answered your 1st question - same problem here.. But on your second questions do you think that its down shifting... like from 2nd gear to 1st gear... does it make a clunk noise? Check it out that might be it... Or it can also be your brakes... going bad? Even when you release the break pedal... the brakes might get stuck to the rotor and still cause the vibration. 939

[topprolmc]

Hello, I think everybone answered your 1st question - same problem here.. But on your second questions do you think that its down shifting... like from 2nd gear to 1st gear... does it make a clunk noise? Check it out that might be it... Or it can also be your brakes... going bad? Even when you release the break pedal... the brakes might get stuck to the rotor and still cause the vibration. 939

It's because the front drive train is binding on dry surface. It is not unique to Trailbalzers....

If his rotors were loose enough that the brakes were binding, his wheels would fly off.

[gmcman]

4HI when I can't see the road and A4HI when I get into a parking lot or on patchy roads. I try not to use A4 just because of the constant engaging and disengaging even if it's not the entire system engaging.

[the roadie]

I posted in a similar thread, since this question comes up a dozen times every start of winter:

Yes, we have an open front differential. That means whether you're in a turn or going straight, the front wheels are allowed to turn at different RPMs. But they're not entirely free-wheeling because of the differential being engaged in A4WD, 4HI, and 4LO. The diff is going to spin at the AVERAGE of the left and right wheel's RPMs. And through the gear ratio of the ring and pinion gear, it will drive the shaft from the transfer case to the front diff at some lower RPM.

The transfer case is not a viscous coupling like some are. We have electrically driven clutch plates that the encoder motor commands to transfer a little or a lot of torque. In A4WD the clutch plates are prepositioned close to, but not engaging back to front until slippage is detected. Then the encoder motor moves the clutch plates closer together and transfers torque towards the front and that takes a short time and sometimes the torque arrives with a jolt.

When you're in 4HI or 4LO, the clutch plates are pushed far together to transfer maximum torque, or attempt to lock front to back. Since it's a clutch that can slip, it isn't a true locker front to back, but it is very close. It gets me up hills even when I have one front tire two feet in the air. It should be leaking out all the torque, but because of the attempt by the transfer case to do 50/50 split of torque, it can't all go forwards. Some goes to the rear, the G80 locker shares it side to side, and progress is possible.

Now to the crow-hop phenomenon in 4HI and 4LO. I've posted on this before. Every six months or so. That effect of driveline bind-up is caused by the different LENGTHS that the front and rear differential are tracing out as you go through a turn. The front diff is AVERAGING the RPMs of the front wheels, the rear diff AVERAGES the RPMs of the rear wheels, but in a tight turn the front and rear diffs are a different distance from the turning point, which is in line with the rear axle. Here are the numbers:

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

With an almost locked transfer case (with 50/50 torque sharing), the driveline will bind up and sooner or later either a wheel will hop to relieve the stress, or a CV joint will pop. Don't do this on dry pavement.

[mack]

Also, not sure if this is related but ever since I bought the truck earlier this year it seems to be having a brake issue or trans issue. When stopped at a red light if I let off of the break slightly the truck will shake forward. It even shakes after the break pedal is completely disengaged (sometimes). It's not bad, but sometimes it's very noticeable.

Thank you

I am having the same issue with my 05 sle. It almost seems like a bad clutch pack in the tranny.