Nothing exotic needed. Ordinary 80w/90 weight gear oil will be fine. Shell, Valvoline, Esso, whatever.

If the vehicle history is unknown you might wanna drain whatever's left in the diff and install all new. Make sure you can remove the filler plug before draining, though :-)

Cheers
DD

 

Hey Doug,
Do the later cars (in my case an early SIII) use the same viscosity?

Thanks!

Jeff

 

Yup. same stuff. You can use 80/90 or 75/90. Whichever is on sale works for me.

Cheers
DD

 

Chevron Delo ESI 80W-90 is one of the best (if not the best) regular, non-synthetic gear oils. It has a lot of approvals from heavy duty truck manufacturers for extended drain (up to 500,000 miles in those applications).
It's a step up from regular GL-5 80W-90 gear oils.

 

Doug,
You don't happen to know the capacity for a drain and refill?

Thanks!

Jeff

 

About 2.25 quarts as I recall

Cheers
DD