Rear End Lub Sierra C3

[aconred]

I usually search for hours before I ask, well I search for days and am now asking.

 

I have a 2001 Sierra C3 great truck love it. About 6 months ago it started making popping shuttering noise when turning. After setting in it for just a second my mechanic said oh that’s your positive track its got dirty lube, I am sure. He changed the axle lubricant with the book recommended 75w-90 synthetic. Helped for a while but did not fix. Well once lube got hot back to the same so here I am asking.

 

What I have found from lots of testing is when the rear end is cold first thing in morning are after setting for a few hours everything works fine. After 10-15 miles on the freeway then into a lot it starts popping and shuttering, after 30 minutes when really hot it pops and shacks worst, the hotter the grease the worst it gets the tighter the turn the worst it pops. After all the searching I have read a lot about the synthetic lube, the additives etc. my thinking is it has to be the lubricant, wondering if I need the additive even though the owners manual does not say. It defiantly when the lube gets hot so wondering if I need to try 75w-150? I am convinced it’s the lube. I am not convinced the owner’s manual is correct. Any info is appreciated PS don’t ever turn into a 7 story parking deck with this problem J

[Z45]

What is the code in glove box, G80? If its say G80, you have a locking differential and limited slip additive is poison to a locker.

 

Is the C3 a 4 wheel steer? They are the only ones with a limited slip differential, also all wheel drive models may also have a limited slip. It will have G86 on the lable.

 

Did they use an additive when they changed it? Hope they did not because its not supposed to be used in a locking rear axle and can cause damage.

 

I would say the synthetic lube you are using is not up to the task, try a better lube. Try Amsoil or Mobil 1. You many need to flush out the system by doing a 2n change after about 50 miles.

 

Limited slip and locker are 2 distinct differentials. One is made to slip a certain amount and the other is made to lock and never slip. Limited slip are normally installed in cars. My CTS has a limited slip rear axle.