i don't know when the last time the diff oil was changed in my truck or if it has ever been changed. i checked the front diff and the oil is kind of a milky brown/gray color so im not sure what bad diff fluid looks like, but i am planning on changing them both soon.

so my question is what diff fluid and weight do you guys recommend? i have read on here that royal purple is good. but i have a G80 in the rear and some people tell me that you need special diff oil for it but i don't remember ever reading anything about that on here. if so what do i need?

 

80w90 dino juice or 75w90 synthetic. Either will do just fine.

Nothing special is required for the G80 rear differential. A lot of people mistake the G80 for a typical posi which has friction clutches that are always under pressure. The G80 does not have pressure on the clutches at all times, only when there is a speed difference greater than ~200rpm side to side.

 

thanks for the reply. thats what i kinda figured about the G80, but i was just making sure. and is that nasty fluid color fairly normal for its probable age?

 

You could have a crack in your vent tube from the front diff that is allowing water in. It should run from the diff up to the top of the radiator core support and have a little filter/cap fitting on the end. Or it could just be condensation from years of use.