Steve's comments improve upon my previous posting.
It makes sense that there would be TWO sprag clutches (overrunning
clutches). That way, if the rear wheels were slipping when backing up,
the reverse sprag clutch would drive the front axle because the rear
driveline would be spinning faster than the front drive line. And, as
Steve also mentioned, it seems that there would have to be a linkage
from the transmission to engage the correct sprag clutch when switching
from a forward gear to a reverse gear.
If the WRONG sprag clutch were engaged, I'm not sure what would happen
without a diagram to view. However, I suspect that this is what might
happen when the vehicle is moving in a forward direction: Whenever the
front driveline turned faster than the rear driveline (as when rounding
a curve on any vehicle designed with understeer), it would cause the
sprag clutch to lock and the front wheels would essentially try to
drive the rears. This would cause a tremendous amount of tension in the
drivetrain when on dry, solid pavement, resulting in possible loss of
control of the vehicle, possible component breakage, and certainly
undue wear. Even when on soft surfaces it would still cause unnecessary
drag and drivetrain tension. It would be like having the front axle
engaged with a standard (non-clutched) transfer case, except that it
would not allow any forward traction from the front wheels.
If BOTH sprag clutches were engaged simultaneously, due to a linkage
problem, I'm not sure what would happen. It might just make the
transfer case act (in both directions) like a standard non-clutched
transfer case with the front axle engaged. But without a diagram, I'm
just guessing. Any ideas?
As to the original problem in this thread, it still sounds like a
transmission problem, as mentioned previously.
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