Strange rear axle wheel drag/chirp

[ComputernerdBD]

Hey everyone. So this is an interesting one.... Last night I drive the truck in snowy weather, first in 2WD and then I switched to 4WD because the wheels spun a couple times, causing the Stabilitrak to take over and throttle back. Bad weather and no plows was not fun but I know not a problem for this truck. Got on the main roads, up to around 45mph in some places no problem. Got home, parked it and left it in 4WD overnight.

Got up this morning to move it for the plow. Got in, took it out of 4WD and had to make a 3 point turn out of the space in addition to additional tight 90 degree turns to get it where I needed to move it to. Was getting resistance (but not as much as if it was in 4WD) and some tire chirping coming from the rear only on turns, and was seeing it in the mirror that the tire was intermittently dragging. 4 turns later and it was still doing it. I back up to park it parallel to my other truck. Not sure if there was snow or something stuck in the wheel or behind it but I think of "What if the differential or transfer case is stuck?" because I have had issues with the other truck hanging in 4WD (so I unlock the PosiLock or shift from reverse to drive a couple times and it unlocks) so I think of trying something unusual. I cycle the 4WD system into 4HI and back to 2HI and put the shifter into reverse and then drive. I grab my wallet (with my AAA card in it) and take a test drive. Could not reproduce the issue. Turns were smooth. Now I am baffled.

So what could I be dealing with here? No leaks and I know the fluid is nice because it was changed less than a year ago with 75W-90. I know this truck has an 8.6" ring gear but GM apparantly has it on file as an 8" for some reason and bought the cover back then from them based on the lookup. Found out the hard way about 3 years ago because the cover had a nice scar in it when I went to change the fluid. Changed the cover and fluid again, no pieces broken off the gear and good as new. Only recent work in that area was removing the rear left wheel to redo the bead seal due to a slow leak. Thanks

Edit: The truck has just over 60K on it, what about the calipers? They are original.

 

[Mounce]

Do you actually have the posi or actually the g80 locker? Sounds exactly like the locker didn't unlock for whatever reason.

 

[ComputernerdBD]

It is the G80. If it didn't unlock before parking due to driving it in the snow, could this be a one-off or could this be signs of a more serious problem? Thanks

 

[Mounce]

Generally should unlock pretty soon if not immediately after the spinning even has stopped.

Couldn't tell you much though, I'm not very familiar with the issues and causes they can have, just vaguely understand how they work.

 

[Chickenhawk]

It's pretty normal for the G80. If it has locked up on a snowy surface, it can sometimes take a bit to unlock it, especially when cold. If you park it and then start off again in snow or ice, it does tend to stay locked for a bit until it gets on a less slippery surface. This happens to me occasionally in the winter when I back it in at night and then leave the next day, across a slippery back lane.

While the G80 technically does not require a limited-slip additive, I have found that a half tube of additive helps sometimes. The G80 is actually a locking differential and not a limited-slip differential, but most 75W-90 GL5 axle lubricants have LS additive already in it. It won't hurt it. If it's been a while since you changed the fluid, I would change it. If you find occasional chatter, add a bit of LS additive. But this is normal and a function of the fact that the G80 is a true locking differential, and not a limited slip like you find on cars.

 

[ComputernerdBD]

So it should unlock soon after a spin event but under some cases can stay locked? That makes more sense considering I came around a corner a bit fast on snow in 4x4 right before parking it where the Stabilitrak kicked in. I think these trucks are too much "fly-by-wire" and the computer won't let it do much stupid (within reason) but I guess since I won't let me spin the tires that much it also protects the drivetrain to an extent. What would indicate however if anything is damaged? If it was would it still be locked?

If I remember correctly, I used Mobil1 which has it in there. I change all fluids in this truck that carry load (engine oil, trans fluid, gear oil, transfer case) on average every year myself (more complex or dangerous items such as brake fluid, coolant or power steering I have my preferred shop do. Trans filter I have done every 2nd or 3rd fluid change (drain plug)) and I only put around 10-12k on the truck in that time. Thanks

 

[Sparky]

The G80 in my pickup has stayed locked on me for a short while after it locked and it took a bit to get it unlocked. Normally is pretty quick to unlock but if it locked due to a spin and then got in a bit of a bind from a turn (like on mine), it can take a bit to get unlocked again.

 

[jhenry999]

The symptom you described is called CROW HOPPING. My quick fix for my wife's AWD Rainier was to remove the actuater motor on the Transfer Case. Four bolts. Essentially making it a 2-WD Rainier. I live in Florida. Its never off-road. Could be the controller? I didn't want to get into any expensive search to fix something I didn't need so I just disabled the AWD by removing the actuater motor.