I have a question about gear oil involving switching gears and carriers.

I have a 2004 4wd Heritage 4.6L w/ 8.8 3:31 now. Which requires 75w90 syn w/ a friction modifier.

I now have (not installed yet) a set of 3.73 w/ the posi locker out of an Explorer for the rear. The tag on the cover reads 75w140 syn and I suppose you would use posi lock/limited slip additive?

My question is...which oil and additive to use. I'll also be changing the front out as well, just not w/ a locker.

Thanks for the help.

SilverNCSU
https://www.f150online.com/galleries....cfm?gnum=3584

 

royal purple is great and it already has the friction modifier in it.

 

I would put a synthetic 75/140 with a bottle of friction modifier in the rear, you can get the friction modifier from ford. In the front just use a 75/90 or 80/90 regular gear oil. No need for the added expense for synthetic in the front.