Recently, Ive heard of guys running gear oil in their G56 instead of ATF and they said it was and very nice difference, shifted smoother and less noise. Any thoughts on this? I would think it would help a little, especially with heat, which I would think help from ripping the teeth out of them. Also, from what I remember it was 75-90 gear oil

 

I've never heard that,very interesting,I would think that ATF would disapate heat faster than thick gear oil though.
My G56 doesn't make any noise but I wish it wasn't as "notchy" feeling maybe gear oil would help.
I've often wondered why they switched to ATF after using gear oil forever. I guess maybe the ATF could help fuel mileage slightly?

 

I read a thread on another Cummins site about using Amsoil MTF 30. Some of the Jeep guys are running the MTF 30 in their 5-speeds instead of ATF and say it is a remarkable change, tranny is very smooth shifting, and also very quiet.

When looking at fuel mileage and the effect of oil visconsity in differentials, I really don't think that the mileage changes with synthetics. The reason I think that is because I have the Amsoil 75w140 Severe gear in my axles and saw NO change in fuel mileage after I put it in. I lost the 'notchy' feeling when I changed to the Amsoil ATF in my G56.

CD

 

I have run 75-90 M1 syn gear lube in other manuals, I got 345K out of a Muncie Getrag but im not so bold with the G56, its a good shifting box as is.

I think the heavy lube might have screwed with the synchros on the Muncie and forced me to shift into first or 2nd before shifting into rev to avoid a pretty major clunk