hmmmmm. Not according to Steve
if I understand him right. Seems he is saying; just like any other differential.. power is sent to what is spinning the most. With no rear driveshaft to another axle attached, then this will create in effect a "spinning" axle and all power will be sent to it, thus no power sent to the non slip axle' which is only axle you have. So in essence, the only axle you have; without the locker on, is getting no drive forces. See post 14 then again starting at 17
http://www.steelsoldiers.com/showth...tion-on-1083&p=1946304&viewfull=1#post1946304
Granted I could still be totally confused.
I have no particular knowledge of the FMTV in this case, but in general, something to remember about an interaxle differential is that when its locked, that is the same as not having one at all. I don't know why, but it seems like there are a lot of folks who seem to think of an interaxle differential as a way to "turn off" one of the rear axles, but that is not the case.
I think a pretty good way to think about it is if you consider the deuce or 5 ton rear tandem axles - the driveshaft between the two rear axles cannot rotate at any rate other than what the transfer case to middle axle driveshaft rotates at. That is to say, the two rearmost driveshafts have the same RPM in any given situation, regardless of traction. In something like a M915 or commercial over the road truck, the two rearmost driveshafts can rotate at different RPMs when the interaxle differential is unlocked. I think where it gets somewhat confusing to people is they don't think of the interaxle differential as a *differential* and forget to understand how all 4 hubs on a rear tandem could be powered. Much like a pickup truck with a regular open differential has power to both rear tires when going down the road, A deuce going down the highway has power to all 4 rear hubs if the traction is equal. A commercial truck with tandem rear axles and an interaxle differential also has all 4 rear hubs powered with open differentials and the interaxle differential unlocked, given equal traction.
I should think a FMTV 6x6 middle axle acting as the rear axle on a 4x4 would require that the interaxle differential in that axle remain locked in order for power to get to the ground through that rear axle.