The Allison 3700SP transmission has a very low 1st ratio of 6.93; quite low for an automatic. 7th is 0.78.
Standard axle ratio is a very slow 7.8 (3.9 diff, 2:1 planetary hubs). Often when repurposed like this they’re regearedto 6.14, the ad doesn’t say. IMHO I’d want a low range, which the truck doesn’t have, especially with 6.14s. Marmon Herrington makes or can assemble after order a MVG-1150 2 spd TC. With nice low 2.47 low range. But very unfortunately 1.09 high range. And a big price tag I’m sure.
The only way to maintain a decent 60 mph cruise with the 2 speed would be a swap to 14.00R20, which would result in ~2200 @ 60mph with 1.09 high range and 6.14s.
An EatonNoSpin differential (Detroit Locker) is available. When Acela does their thing on FMTVs, a rear NoSpin is standard. And IMHO again, essential. In the front? Hard to say.
I have no interest in acquiring or selling FMTVs, this is just information I’ve acquired over the years.
One last thought re 2 spd TC: people always say “torque converter” as an excuse for no low range. Well, that doesn’t help going downhill. With an RV, you’re carrying “everything including the kitchen sink” and there’s inevitably loose stuff, so slow is good. 6.14 is definitely faster than the original design 7.8s.
The lack of low range is probably best understood as a cost savings for the gov’t and considering the (possible lack of) intelligence and offroad experience of the intended young GI drivers and availability of recovery equipment… Likewise the lack of locking differentials….
Yes it will definitely run on high sulfur diesel without problem. In fact, it’ll probably be fine with Jet A. But not Jet B.
expeditionmeister.com
