Doug1964

Can I use any gl4 gl5 85w90 gear lube or do I have to use pure mineral oil 90 weight. I have a non posi rear diff. 1960 low hp 3.70 gears

DZAUTO

Yep, you're good with either one.

Tom Parsons

C1-Curt

What do you use in a 60 if you have a posi?

DZAUTO

Use a quality GL4 or 5 80w90 (85w90).
The MAJOR concensus of opinion for trannys such as the T10 or Muncie, should only be GL4. Thus GL4 is all I have. But since there is no brass in rearends, then GL5 is OK.
I buy GL4 in 5gal buckets because I build 4spds and rears.

Tom Parsons

Frankie the Fink

Errr...Tom I think he's talking about the differential and the 'friction modifier' that the old posi units require. But I could be wrong of course.

capevettes

I use 80/90 gear weight oil and one 4 oz bottle of GM posi lube in my 61 rear end with posi

DZAUTO

And you're absolutely correct. I thought he was just inquiring about the lube itself. So, yes, with 80w90 (85w90) gear oil in a posi, also add a bottle of GMs posi additive. MOST of the time one bottle of additive is sufficient, BUT on a few ocassions it may take 2 bottles if a posi is rebuilt with BOTH a pair of Belleville plates and a pair of Belleville discs.

Tom Parsons