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I think Michael is essentially correct. I believe the M135 has a gear
reduction unit that is bolted directly to the rear of the Hydramatic
transmission, and this unit provides the high and low ranges. The transfer
case function is just to engage/disengage the front end, using a built-in
sprag (or sprague) clutch (this is a one-way clutch that grabs in one
direction and slips in the other). The sprag clutch drives the front axle
only when the rear driveline is turning at a faster rate than the front
driveline, as when the rear wheels are slipping. Please correct me, anyone,
if I'm wrong. I don't know much about M135s.
Reverse would be provided internally by the Hydramatic transmission itself.
As I mentioned to you offline, it is probably a modified civilian Hydramatic
that was used in the M135. I don't have the M135 manuals, but if I knew
which civilian Hydramatic (there are several possibilities) formed the basis
for the M135 transmission, I might be able to look up its functional
diagrams and narrow the problem down. If you're moving forward when you're
in reverse, I have a sneaking suspicion that the neutral clutch may not be
releasing, but that's only a hunch. The same problem could also cause the
vehicle to move while in neutral.
Alan
(Salt Lake City, Utah)
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