I went to go get some gear oil to change my tranny and diff. I knew I needed GL4/GL5 and always have used royal purple in my engine so went for that. I was looking for 75W-85 that the dealership service guy told me, but they only had 75W-140. The guy at the parts store said RP stoped making -85 and now only made -140 which is better and is what I should use so I bought it. Before I put it in though I want to hear it from someone else, is it OK? Am I going to be loosing any performance? It is for hot weather climate (Miami) if that makes a difference.

Thanks!

 

be sure to use a GL4 in the tranny. and be sure to use GL5 in the differential. i've been advised (by exxonmobil and redline engineers) not to use GL5 in where GL4 is recommended.... something along the line of the additives in GL5 can be harmful to synchros.

as far as the royal purple's weight... that's a bit off. I would recommend you to stay at (or very close to) the factory-recommended viscosity; unless you have a specific reason not to.

 

It is both GL4 and GL5 so it is good to go for both, just not sure about viscosity. I would be more comfortable with going exactly with the recomendations, but the guy at the parts shop said it was an improvement. I dunno how viscocities work though so...

 

I have been using RP MaxGear 75W-90 in the rear diff for the past 15K miles, no problem. And I recently saw MaxGear 75W-90 at the local parts store.

 

Has anyone used Amsoil synthetic 80W-90 for differential?
http://www.amsoil.com/StoreFront/agl.aspx