Hey Guys,

Need some suggestions. My cousin has an 04 Rainier that sounds like a standard wheel bearing hub humming. But I've had a car that I changed both hubs on that still made the noise and ended up in the transaxle, so I wanted to further diagnose this Rainier before replacing bearings. I jacked up the front and hand spun the tires to listen for humming, I could faintly hear it in the Front diff, not near the hubs. So I jacked up the rear as well and put the car in gear and the front idfferential made a nasty chatter, so I'm afraid something is wrong internally.

I started taking things apart to get the diff out. I pulled out the CV axle and spun the yoke in the diff and the clicking no longer existed, but nothing appears wrong with the spline on the axle or the gear that it slips into. Any ideas?

AWD seems to be working fine, just hums. I was on wet pavement and gased it a little hard and felt the rear tires spin then the front tires spin then off I went. She mentioned it handles like crap in the winter and hates it, so when I was on a gravel road that had a 90 degree curve I gased it pretty good coming out of the curve and it went completly sideways like I hit black ice and it pulled me right straight into the ditch while laying on the brakes. But backed right out on second try with a little bit of a drive to reverse drop.

I dunno exactly how the AWD system works on this and why it pulled me right into the ditch, but I have power slid MANY different vehicles around that corner MUCH faster than I was going with this Rainier, including 4x4 trucks. On a hunch that AWD works much different than 4x4, I later took my wifes Chrysler Pacifica AWD around the same corner and replicated my actions and the AWD kicked in and gave me complete control and slid around the corner just like I have with my truck in 4x4. I dunno what the differences are between Chrysler and GM AWD systems, but I told my cousin she is trading this Rainier in as she is NOT driving it in Michigan winters with kids in the vehicle.

Anyway, thought a little handleing backstory would help diagnose possible issues. Any help is greatly appreciated.

Thank You in Advance,
Eric

tire size and pressure is critical on awd, so thats what i would check first after that,
i only really know about the auto in my yukon but there is a clutch that modulates the front. i would guess normal should be opposite on a vehicle like that but regardless the problem likely lies in the diff and sometimes the noises go away when unloaded so the garage test may not really help. sometimes its just fluid, sometimes its a leak that let the fluid out then took out something inside.

I was under the impression that AWD worked just like 4X4, except it was engaged all the time, and the difference between front and rear were the clutches. I guess similar to that of a AutoTrac transfer case in a Blazer?

I'm not familiar with the Rainier AWD systems. Could you take a picture of the differential that you are working on?

autotrac operation;

During normal driving situations, the transfer case can operate in the Auto
4WD mode. In the Auto 4WD mode, the transfer case shift control module
monitors rear wheel slip speed, based on the inputs from both the front and
rear propshaft speed sensors. When the vehicle experiences a rear wheel slip
condition, the transfer case shift control module sends a pulse width
modulated (PWM) signal to an electronic motor, which is the transfer case
encoder motor. This motor rotates the transfer case control actuator lever
shaft, applying a clutch pack. This clutch pack is designed to deliver a
variable amount of torque, normally delivered to the rear wheels, and
transfers it to the front wheels. Torque is ramped up to the front wheels
until the front propshaft speed sensor matches that of the rear propshaft
speed sensor. Torque is ramped down to the front wheels. The process would
repeat if rear wheel slip is detected again.

I CAN take a pic, but not till this weekend. Vehicle is my cousin'* and she lives 2 hours away...but even when I take the pic, finding someone with internet up that way is troublesome as well, so I may not be able to up load it till the following week...and wait for responses then try them out the next weekend...etc. I realize this makes it very inconvenient and hard to provide assistance, but unfortunetly, I haven't much choice and just don't have much experience with AWD or 4x4, or really differentials as a whole, but I am very experience with cars in general.

i would check the fluid, if its low that could be an indication of why it failed. the clutches probably need fluid to work so that could be why it doesnt work or why it failed

Changed the fluid, it seemed a bit low, but who knows for how long...it also seemed pretty thing for gear lube so I just drained it and put all new in. AWD works. I've talked to a couple friends who have Chevy trucks with auto4wd, and they say they hate that too as it seems to engage way too slowly...which is exactly what this Rainier felt to do. It waited till I was sideways, then kicked in front wheels and sucked me right into the ditch. So it seems to operate normally...it just isn't as good of a system as I am used to. I really just need to get rid of the nasty humming so we can sell the vehicle and get something that handles better and gets better MPG.

nevermind i was thinking it was the one like the aztec, but its the trail blazer one. heres some good pics. if you scroll down there is a pic of the axle removed that part you bolt to the diff has to have a bearing in it.

Offroadtb.com Front Axle 4WD Disconnect

Yeah, that'* the passenger side. My hum is on the driver side and disappears with CV axle removed.

i dont use mine i did a couple times just to see if it works but i either use 2 hi or 4. the direct 4 is more stable, and predictable. i told the wife if she drives it too same deal. 2wd is fine 99 percent of the time anyway if you got decent tires. my yukon has a locking rear im guessing this does too because on a truck that doesnt it stays in line more but with that and 2wd its fine to get you most places and if you need it to get out of a driveway or parking lot just use it for a few seconds then leave it in 2