jj3500

servicing my diffs in my 89. What is the desired fluid for this rear? brands....and also, synthetic or regular. While I'm at it, transfer.

Thanks!

wannadiesel

Depends on the use. If it's just puttering around town and hauling an occasional bed full of dirt, standard 80W-90 is fine. For heavy towing, I'd put an 85W-140 synthetic out back. Dino 80W-90 is fine up front no matter what the application.

Transfer case gets 80W-90 as well, no need for synthetic there either.

93beater

80/90 in front and rear with a limited slip additive, i run 80/90 penz gear oil with the 1/2 quart of lucas motor oil additive in front rear and t case, helps the clatter, thickens the oil for less breakdown, imo its better than any limited slip additive, and i work @ a lube/mechanic place so i see this a lot! good luck for lots of pulling and heavy haulin 75/140 should do the trick but dont forget the lucas, or some additive its a must!

bigredbrick

I'm running Royal Purple in both diffs, 80w-90 in front and 85w-140 in the rear. Straight 50 motor oil in the t-case.

dpuckett

I run a synthetic 75-140 in the rear, with 2 bottles of friction modifier just to make SURE it doesnt grab around corners in town.

T-case will get the same oil, and the front probably will, too.

I think anywhere you can run a synthetic and cut down on frictional losses is good, esp with $4+ diesel.

Daniel