Synthetic gear oil in old crusty rear end.
 

I've done a search on here and Google. A lot of people are running synthetic gear oil in these rear ends.But no one is stating if rear end has been rebuilt or if it is the original.I guess the synthetic has the advantage of not needing any additives.If I run synthetic will it jive with the old mineral oil that's left in the rear end? Will the synthetic do anything to the old seals? I'm probably over thinking about it lol.IMG_20200708_171958.jpg

Re: Synthetic gear oil in old crusty rear end.
 

Differentials in old cars and trucks will last for decades, and hundreds of thousands of miles, with the original 80w-90 conventional gear oil. Most old cars and trucks never even had the gear oil changed, and still they lasted forever. I don't see any benefit to spending the extra money for synthetic. I run 80w-90 conventional in all my old vehicles.

Re: Synthetic gear oil in old crusty rear end.
 

I recently rebuilt my C10 rear end. I bought a new Eaton positraction unit for it. They recommended conventional oil and posi additive.

If you have an open rear or some other type of limited slip then the synthetic is OK.

Re: Synthetic gear oil in old crusty rear end.
 

I'm probably just going to go with the old style gear oil.Not for sure if I have a posi rear.If I do is the additive something I can purchase from the local parts store?

Re: Synthetic gear oil in old crusty rear end.
 

It sure is, any auto parts store will carry it, you can also purchase it online.

Re: Synthetic gear oil in old crusty rear end.
 

Thanks for all the replies.Took the cover off and I don't think I have the posi.I guess posi's have a spring in the middle and mine does not have it.IMG_20200715_172509.jpgIMG_20200715_172524.jpg

Re: Synthetic gear oil in old crusty rear end.
 

You have the standard open differential. Looks pretty good. Button it up and fill er up.
Jimmy