I have a '98 SS with the Auburn differential. The car only has 10,500 miles, so I've not needed to mess w/ the diff much. The recommended fluid is 80W-90 mineral base oil w 2 ounces of GM Lubrizol. Can I run AMSOIL 75W-90 synthetic in this diff, or am I asking for trouble? Why or why not? Do I still need the Lubrizol w the AMSOIL? Do I need different gasketing materials? If I can run the AMSOIL, how far does it extend the change intervals? Thanks.

 

Why not just pose this question to the guys at Amsoil? I'm sure they've been asked similiar questions by other customers. May even be in their FAQ section, if they have one.

-Mindgame

 

Better yet, pose this question to someone who works at Auburn Gear. In fact, I did, as I have an aftermarket version of the Hi-Performance LSD in my GTA, which is probably the same one you have in your car.

I have been running Mobil1 synthetic diff fluid and the GM additive for about 3 years now and have not had any problems. Unit keeps positive power to both wheels all of the time and has never chattered.

I recently asked my close friend, who works at Auburn Gear, what he thought of Synthetic diff fluid. He said that they (Aurburn Gear) did not recommend running synthetic lube because it could cause the unit to chatter badly when you go around corners.

However, like I said I have been using syn fluid for about 3 years in this diff without any problems but it has the GM additive as well. I will say that my friend said that the additive was probably the reason why I haven't had any problems.

Its up to you, but I would run the syn fluid and the additive...

 

For the most part, I’ve gotten away with synth (Mobil 1) and no additive with all the GM posi’s I’ve messed with, with no chatter. Not running the additive will result in better posi action, but could also result in chattering and premature wear.

I’ve never heard of differential manufacturer’s unhappy about synth fluid, possibly with the exception of being a little too slippery. There are a few gear and rear manufacturer’s that recommend against them claiming that conventional is stickier and has a better film strength which better protects the gears under heavy loading.

FWIW, I’ve gotten superstitious about Amsoil gear lube. Both times that I’ve tried it I’ve blown up a set of gears within 400 miles… probably unrelated but I won’t run Amsoil again.

 

Auburn specifically recommends against synthetic gear oil. Check out http://www.auburngear.com

2.) What kind of oil should be used with an Auburn differential?

It is important when installing Auburn differentials that a high quality, non-synthetic 80w90 GL-5 oil, treated with GM or Ford limited-slip additive (also known as friction modifier) be used. Three ounces of additive will treat one quart of oil.