I got a buddy with a 2002 Sierra, he says when driving slow and turning, like pulling in and out of a parking spot the rear tires lock up. i witnessed this today. while turning one wheel is stationary and the wheel on the outside of the turn spins then locks and starts chirping or skidding. Is the G80 locking up? is it toast? once he staightens up and drives straight it stops and the wheels spin free. Oh, its also 4x4 if that matters.

 

Sounds like spider gears are jacked...

 

It's quite possibly toast. Jack the back end up and see if you can rotate one of the tires by hand. If you can't, the grenade has exploded. If you can and the other tire rotates in reverse, then you may need a differential oil change (or the grenade pin has been pulled and you're counting down the seconds).

 

I thought it was suppose to "rotate in reverse"? doesn't that mean its working?

 

That's what I said. If the tires aren't locked to the driveshaft, then the spiders aren't frozen. I'm offering a solution that may/may not fix his issue.

If the tires were to fail to spin (in park) that means that the spiders are frozen and you're now turning against the parking pawl.

 

Welcome to the world of a 10 bolt G80.. Its junk. My 03 lasted 43k before i blew the first rear end.. Same exact symptoms. Pulled the cover and i had more spider gear chunks laying in the pig than what was left in the carrier. Time to spend some money on a LSD or a Trutrac