so while i was doing my brake job last weekend i had all 4 wheels off the ground i put the tires back on, started the engine and shifted into drive. i had somebody outside confirm all 4 wheels were spinning, so i think there is a problem with the AWD system. its supposed to be in RWD only until slip is detected then it goes to AWD right? if all wheels are spinning would this mean there is a problem with the encoder motor on the transfer case? or the TCCM? does the AWD use the same vacuum system as the 4x4 models? what should i do? all i know now is my AWD is always engaged and i think its robbing my MPS's last fill up i got 12MPG

i am also working on acquiring a new charcoal box which is also contributing to lousy MPS's but this thread im trying to fix my AWD, unless im wrong with how it works

 

If the AWD works like the 4-button in auto mode (but without the front axle engagement/disengagement), there is a preload in the transfer case that would cause the front wheels to turn (because it is always ready to engage). As far as a 4WD vacuum system I don't believe the AWD has one since the front axle is always locked in. 12mpg is pretty normal for non-highway driving in the Winter. I don't think you have a problem.

 

The NV136 transfer case in your Bravada has a preloaded clutch pack on the front output. This means that some power will be transferred to the front driveshaft and the wheels will spin. So there is nothing wrong here.

There isn't any form of disconnect in the passenger side of the front differential on the Bravada. Just a solid shaft from the differential side gear to the CV shaft.

The NV236 used in the Auto4wd models has the same clutch setup, but with a disconnect in the passenger side output from the front differential. It will spin the front driveshaft pretty much whenever the rear of the vehicle is off the ground and transmission placed in drive, but will not spin the wheels without locking in the front axle disconnect.

 

so i have nothing wrong with my vehicle? i thought they were just 2wd until it was needed and the TCCM does all the work

would it be normal to feel some wheel hop and resistance in acceleration as im pulling out of a parking spot and turn the wheel hard?

 

Wheel hop & resistance while turning isn't normal. The preload on the clutches isn't that much. You should be able to jack up one of the front wheels and turn it by hand. It should not free wheel, but shouldn't have so much resistance that you cannot spin it by hand.

Wheel hop & resistance while turning means that there is likely a fluid quality problem in the transfer case. I would recommend you start by pulling the fill plug (higher of the two plugs on the back of the transfer case) followed by the drain plug. If fluid comes out of the fill plug, you will have to remove the transfer case and replace the input seal. If no fluid comes out of the transfer case, you can drain it and refill with AutoTrak II fluid and ONLY AutoTrak II fluid. Drive it for 500-1000 miles and see how it is reacting. If it still is acting up slightly, I would recommend another fluid change.

 

ok ill try that. it just so happens that i have a couple qts of AutoTrak II in my garage bought from my local GM dealership parts dept. how many qts would it take to fill the transfer case?

 

Should be just shy of 2 quarts to fill.