[sjb5856]

Can someone offer advice on the best oil for replacement of diff oil 8" 1966 standard diff

 

[squekster]

Can someone offer advice on the best oil for replacement of diff oil 8" 1966 standard diff

I prefer 75w/90.

 

[Ivy66GT]

50 years ago Ford had a different gear oil for 'high performance' vehicles but with today's improved specs I don't think it makes much difference. Any good GL-5 gear oil would work. If its a limited slip you might, or might not, need an additive. If the limited slip groans when driven then it needs the additive which Ford still sells. As I recall the original Ford oil was an 80W but few gear oils today are single weight. Any GL-5 similar to 80W-90, 75W-90, 75W-140, etc., should be fine.

The GL number is the load rating. They did away with GL-6 which was supposed to be the oil for the heaviest gear loading making GL-5 the best rating you will find on the shelf today. Lower numbers like GL-1 are for more lightly loaded gears and not something you want to use in a differential. If you can even find GL-1 it will likely be called manual transmission oil since manuals don't really need a gear oil. Many manuals today use ATF so that they shift better.

The GL ratings are an API (American Petroleum Institute) thing but I am pretty sure the same standards are used in OZ.

 

[Tony 64]

Hey mate, I used Valvoline SAE 80W/90 High Performance API GL-5 available in 1 litre bottles.
I think I used nearl 2 of them.
I got them from Scott's Auto 1 in Sydney, not sure about Perth but any good auto spares shop would have them.

 

[RF Mustang]

Go to your local Ford Dealer and get 2-quarts of : Motorcraft XT-4-QGL.