Heres my setup:
- HP30 with 4.88 USA Standard gears and an Aussie locker
- 29 spline 8.25 with 4.88 USA Standard gears and a limited slip

The rear has a nice little whine, so Im going to pull the covers and check the backlash on both diffs. If backlash is in spec, Im thinking some heavier gear oil could be beneficial.

Anyways, what weight oil should I use? I have 80-90 in it now and was thinking of 140? Should I just stick with 80-90? I was informed by the guy at autozone that 80-90 was the wrong oil according to the computer. But should I go by what chrysler says, or what U.S.A. Standard says?

Also, Do I need to add any friction modifier for my limited slip and Aussie locker?

 

80/90 is fine and you need the friction modifier for the LSD but not the aussie. I run a synthetic blend with lunchbox lockers, tends to make them a little quieter. Full synthetic would prob do even better but it cost too much when you change the oil every other trip out.

 

what did he say they suggest? 75w-90, 75w-140? straight 90? I run 75w-90 in mine.