The rare AWD Tahoe and some questions.

[TTro33]

I just put on some new wheel bearings and noticed every time I tried to jack up the front end the Tahoe on a slight rear end decline would move backwards. So after putting some chocks on
the rear tires and finishing, I moved the Tahoe to level ground and jacked up the rear end. The tires spin freely, the drive shaft would make little movements as I spun the tires.

Is my rear diff obliterated, and I been using just front wheel drive for the two years I've had this? ? I was thinking perhaps it engages when in use, and since the traction control, stability control is disengaged because after fixing the wheel sensors trying to solve the error messages and not being able to push to engage the 4 lo button I had to leave one of the rear ones unplugged because when I did fix them, whenever I pushed on the brakes I got this weird push back like the brake petal was moving up and down against my foot, not abs stuttering. I even had the ABS module rebuilt and no fix, but that's a separate mystery, or maybe the cause for the rear wheels spinning freely when jacked..

Anyone familiar with this system? Does traction control and stability need to be working for the rear to get power? Any help would be appreciated, and I do everything possible to avoid a mechanic, so far so good.

 

[01ssreda4]

What your describing sounds normal.

 

[M1Gunner]

Obviously depending on your gear ratio the prop shaft is going to spin at a different rpm than the rear wheels. But if it's not continuous or if it's got a slight jerk or stutter then the gears are not meshing correctly. (If your tires move in an OPPISITE direction and the prop shaft doesn't move, that's normal) On an AWD the rear wheels may move ever so slightly when lifting the front end but it should be a very minimal movement. They should not move freely in the SAME direction unless the transmission is shifted to neutral.

With the trans in park, if you're able to lift the front end off the ground and push the vehicle forward or backward without the rear ended locking then you're gonna need to overhaul the rear end.

 

[TTro33]

I kept jacking the front up to work on it and it would creep back a little, start again and it would creep back more. With only the rear jacked up in park the wheels did spin in opposite directions without moving the drive shaft. How would I got about testing to see if the rear is getting power then? I can't jack up the front and scoot the rear around, I'm working on a gravel driveway. All I can think of is to jack the entire thing up and try but it's a pain is the rear since I'm working with a small rolling jack that I need to put on a wooden block to even get it lifted and then use many blocks to keep it up. Going to have to buy a bigger one.

Any ideas on why my brake petal starts pushing back when I hook up all the speed sensors and fix all all the traction control and stability warnings? Perhaps the rear doesn't get any brakes when the traction control is turned off and when on the rear disk rotors are severely warped and make that feeling?

 

[M1Gunner]

Warped rotors will give a pulsation feed back in the brake pedal.

Pull the codes for the TC and ABS that will point you in the right direction. It's possible that your rear end could be causing that giving a mismatched wheel speed reading which will diasble TC and ABS. You said you have two rear wheel speed sensors though? What year is your truck?

 

[TTro33]

Yes I know, but the brakes feel fine so long as I leave one of the wheel speed sensors unplugged which disables the traction control and another feature and the ability to lock into 4 lo on this 2005 Chevy AWD Chevy Tahoe. When I plug the sensor I replaced back up the Traction control, stability and ability to lock in 4 lo comes back and work only the brakes start doing that thing, which is why I asked if maybe the rear wheels are only given brakes and/or power when the speed sensors are all hooked up and working. When I first got it the front speed sensors were bad so I replaced the bearings, and one of the rears was bad and replaced it trying to fix the service stability warning. I buy the cheap ebay bearings they seem to last a little over 2 years. For $65 that's not bad. I even buy my tires off ebay, then pay someone $20 to put them on but save over a hundred.

Back to easiest way to find out if the rear is getting power, I guess I will just have to jack the whole thing up, put it in drive and see if the rear wheels turn.

 

[6speedblazer]

On an AWD the rear wheels may move ever so slightly when lifting the front end but it should be a very minimal movement. They should not move freely in the SAME direction unless the transmission is shifted to neutral.

With the trans in park, if you're able to lift the front end off the ground and push the vehicle forward or backward without the rear ended locking then you're gonna need to overhaul the rear end.

On an all wheel drive its perfectly normal for the truck to roll around if the front wheels come off the ground(or if an axle/driveshaft is removed too). The AWD trucks run 3 open differentials. Front, Center and rear. With the front wheels off the ground there is no resistance in the drive train and the open differential in the trasnfercase allows the back wheels to roll. the front wheels or wheel should turn the same amount as the rears. just like when you jack up the rear on an open diff and spin one tire forwards the other spins backwards the same distance.

The locking mechanism for park is internal in the transmission, thats upstream of the transfercase. upstream of where the "slip" is happening when a wheel is off the ground.

In the future to prevent the truck from rolling, chock the rear wheels or set the parking brake.

 

[TTro33]

Thanks for the help and knowledge. I am going to jack the whole thing up and do some tests, see if the brakes are working on the rear, perhaps the rear rotors are warped and when I plug the rear wheel speed sensor so all the systems are working, the rear gets brakes and then the warped rotors make that brake petal feel? I would feel silly if that's been the issue all along.

 

[01ssreda4]

Thats absolutely correct about the awd models having open diffs, I was disappointed when I opened mine up and found i didnt have a locker/posi.

 

[about20ninj45]

Can you add a locker to an awd system?