So i got the axel fixed and did seals and bearings on both sides- drives great everythings cool.

I notice now when im doing very very sharp U-turn style turns I get a howl from the rear.

WTF?

 

after checking could this be because the shop didn't use GM LSD additive?

I've run into this problem once before but my rear end clicked and popped when it was going in reverse when non GM additive was used.

 

update: it only makes the sound when the diff is hot (15miles of driving) and the shop owner said he did NOT use GM additive, rather its an aftermarket brand.

can I just add the GM addtive on top of the generic crap or should I just take it up to them for a full drain

 

well since you have to drain some out anyways to put the GM additive in, I would go ahead and drain it all. Just to be on the safe side.