Can anyone recommend a good Differential gear oil for my 65 Mustang 289v4 with a conventional rear end (not Traction-Loc)? I am just going to siphon out the existing oil through the filler plug and re-top the differential with new oil. I do not want to mix what's in there with new synthetic oil.

One on-line article suggests API GL-5 High EP, but another article said to avoid High EP in classic cars because the high sulfur content may damage phosphor-bronze components used back then.

Also, I have been using transmission fluid in my 65's power steering. Is this OK?

Thanks

John

 

Trans fluid in the power steering is okay. I would avoid the High EP just because I think it would be overkill. Regulay ol' 80-90 gear oil is what I would use. Be sure to get a gear oil pump to put the new stuff in or you will be cussing it. They are just a small plastic hand pump that screws onto the gear oil bottle. They are pretty cheap and will make it a bit easier to get all the oil in. Come to think of it, you can attach an extra chunk of hose to it and use it to suck the old stuff out too. When you see one you will understand what I mean.