So I was in the parts store picking up some royal purple 75W-90 and asked the clerk to look up for sure how much each differential took. He said that the back took 2 and front took 1.5 but that I was using the wrong lube. He said I should be using straight 90 weight.

I have used 75w-90 in the rear and 80w-90 in the front. What does everyone else use?

 

The '96 service manual calls for 80W-90 in both front and rear.
Amsoil says 80W-90 for 1993 as well. But on their product guide, provides links to 75W-90 and 75W-110 as well.

I've used Mobil 75W-90 and 75W-140. Coming up on changing it, will go with 75W-90, probably Royal Purple.

 

Royal purple 75-90W with the additive for limited slip and locking differentals

 

What additive do you use? I am currently using Lucas oil in both differentials. Whats the difference between lucas and royal purple? I know that royal purple is a full synthetic, so it will have smaller molecules that coat the metal better. I thought lucas oil did that as well?