AX15 with Cummins R2.8 Gear Oil

Oct 5, 2020
I am in the process of swapping a Cummins crate engine R2.8 diesel into my 1997 Jeep Wrangler TJ. The AX15 has a torque rating of 300 ft lbs, the little Cummins puts out 310, so it's close, but I want as much protection for the gears in the transmission, especially 5th gear due to the torque and also the possibility of turning up the power a little and might be at close to 400 ft lbs. Right now I am looking at Redline 75/90NS gl5, this is designed for transaxles to also allow manual transmission use hence the no slip designation. Any thoughts?

Nice swap. The AX15 shifts better with a GL4 or Synchromesh type fluid.

It's not going to last long behind that engine. As a long time Jeep guy with my own swaps (Jeep 2.5L to SM420), you'd be better off swapping to a more robust tranny with a higher torque rating right off the bat. Even a 3550 or 370 would be better.
Don't use GL5 in the AX-15, which has brass synchros. Use GL-4, I currently have Redline MT-90 in mine, and it is recommended by a few AX-15 suppliers.
I remember using Coastal GL4 in my AX5 before swapping to my SM420, 20 years ago. Come to think of it, I use the same in my SM420 because GL5 was notchy.
Redline actually recommends this oil for use in the AX15, my goal is trying to prevent 5th gear from self destructing under high torque loads. My other choice would be to use Redline MT90 which is a gl-4 oil. My AX15 currently doesn't have any issues, and I am pretty easy on parts, but diesel torque can tend to be hard on things. Years back I swapped a 24v 5.9 cummins into a 1985 Suburban with a GM NVG4500 tranny and 32 spline output shaft. The output shaft would destroy the splines in 5000 miles until I swapped it to a 23 spline dodge output.