I apologize in advance if I'm being repetitive but I haven't read all the posts in this thread, and I do see that I posted at least once.
Almost a year ago I was finishing the trip in my '84 M923-A1 from Ft. Benning, GA. after leaving it at my daughter's place for a year (long story) 80 mi. south of Ft. Worth, TX. In Kansas the temperature got as low as -20 degrees and we had to lay over in Hayes, KS for 2 days. It was even nastier from there to Denver, CO. We left it in a Walmart parking lot, 16 miles from the storage yard for two days. When we went back to finish the trip, low gear slipped, then started to work. I sat for about 2 minutes in neutral in a turn lane and when I dropped it back into gear, it didn't move.
Long story shortened, I called Allison and had a long talk about that transmission and what to do about it. The engineer there told me that the MT654CR has a custom low gear pack. He also said the Army DOES USE 15W40 and to "GET THAT GOVERNMENT S**t OUT OF IT". He told me that Allison used to recommend Dextron but don't anymore because they are no longer affiliated with General Motors. It's still good stuff, though.
No matter what the lude manuals say, use any good ATF. The 15W40 works in above freezing temperatures, but can fail to lube the low gear pack in below zero temps. I bought a pull-out from Glen (91W350) and followed the Allison engineer's recommendation. Thanks again, Glen, it was good doing business with you.
