Gear Oil - GM Synthetic 75w-90

[jpoole]

I have a 1983 Hurst / Olds and am swapping in a 8.5 3.73 gear Posi from an 86 442. I was wondering if anyone has used the GM Synthetic Axle Lub (89021677) with new Grap scent... 🙂 in their older GM rearends.

Also, does this stuff need friction modifier? and approximately does an 8.5 10 bolt hold?

Thanks, Jeff

 

[pontiacgp]

I use Amsoil synthetic in my 67 Eaton posi rear without any additive and it works great but I would not use synthetic or additive if it's an Auburn posi. If it's an Eaton use the synthetic and if it chatters then you can add some additive.

 

[jpoole]

It is a stock posi. Also have some GM 88862624 75w-90 Dexron, would that work and how many qts?

 

[pontiacgp]

4.25 pints is what the book says, which is 2 quarts + 4 ounces

 

[jpoole]

Thanks got 3 qts of each. Anyone ur either or hav opinion of them?

 

[pontiacgp]

what posi do you have, Auburn or Eaton?

 

[jpoole]

I don't know stock GM from 86 442.

 

[pontiacgp]

it's easy to find out, remove the cover.

 

[jpoole]

How do u tell?

 

[pontiacgp]

when you look at the carrier the Eaton has clutch packs, you will see the cut out on the carrier for the tabs on the clutch packs. The Auburn has cones behind the side gears that you won't see unless you dismantle the carrier. This is an Eaton posi with the S spring and you can see the cut out and the tabs of the clutch pack. If yours is an Eaton it may have the S spring or a 4 spring set up