What Weight Gear Oil Should I Use?

[RustRocket]

Hello all, I have a 7.5" in my car and I'm wondering what's the right gear oil to use. The crappy Chilton book doesn't say and google doesn't yield anything. Just a good old stock GM 7.5" with a little aluminum tag reading "USE LIMITED SLIP DIFF LUBE ONLY". Before you ask, no, I do not have the RPO code list to determine if it is LSD, and I'm not exactly in a position to jack the entire rear end off the ground(parked on a hill, brakes don't work right, transmission is having some issues). Anyway, if y'all could let me know what I should use, that would be great

 

[williamattop]

The old 80w90 stuff plus GM posi additive always worked great for me.

 

[Yav8]

Any good gear lube will work, just be sure you use the additive for the posi. or it will clunk and bang.

 

[pontiacgp]

You'll find out if it's posi when you take off the cover to drain the lube. If you use synthetic lube that has the posi additive in it and synthetic will let the rear end turn easier.

 

[RustRocket]

I found the code on the axle tube, it reads 2bc, and according to the sticky thread here I think that means 3.08 LSD? I ask because it seems every car is different. For example the Astro takes 80w-90 and the Mustang takes 75w-140

 

[L92 OLDS]

You'll find out if it's posi when you take off the cover to drain the lube. If you use synthetic lube that has the posi additive in it and synthetic will let the rear end turn easier.

Synthetic is good stuff but be aware that some posi carriers will not work properly with it due to reduced clutch holding effectiveness. I discussed this at length with engineering at Auburn and had a noticeable issue with a factory Eaton. Most Auburn's require old school 80w-90 with their additive. I use the GM stuff and it works fine.

 

[pontiacgp]

Synthetic is good stuff but be aware that some posi carriers will not work properly with it due to reduced clutch holding effectiveness. I discussed this at length with engineering at Auburn and had a noticeable issue with a factory Eaton. Most Auburn's require old school 80w-90 with their additive. I use the GM stuff and it works fine.

yes your right, I should rethink that one.