I want to change the oil in my rear diff. What is recommended? Do I need to add a hypoid additive? Is synthetic much better?
86 XJS

 

Nothing special required. I use whatever name brand gear lube that's on sale that day: Valvoline, Quaker State, Shell, whatever. I use 80/90 weight. Yes on limited slip additive unless the bottle says the contents is already formulated for LSDs. I use GM 1052358 or whatever the parts store has on the shelf. They all seem to work the same, IMHO.

Synthetic is fine if it makes you feel good. But not required.

Cheers
DD

 

I'm also thinking about doing mine... Will one quart do it?

 

Buy two quarts. "3.25 US Pints" is what the manual says.

Cheers
DD