Re: [MV] Sprag problem. Doesn't work in forward. Ok in reverse

From: DDoyle9570@aol.com
Date: Sun Aug 19 2001 - 07:11:15 PDT


I presume your truck has an overrunning clutch sprag rather than air shift...

This is fine, and the solution probably is NOT replacing the sprag, either
with the same kind or an air unit.
Rather, the solution is the proper adjustment of the sprag linkage.

The proper method is described in detail in TM 9-819, and I'm sure other
places as well.
I'm not at home now to quote it, but I will describe in general the procedure.

With engine off, jack up one front wheel.
Put transmission in reverse, turn wheel backwards, try to turn it forward.
It should turn freely backwards, but on move an inch or so backward.
Put transmission in neutral. Wheel should turn freely forward, but not
backwards.

If your sprag unit does not behave this way, more than likely the linkage
needs adjusting. This will require you and a helper (two helpers are
actually better, one to shift, one to turn tire, and you to turn wrenches).
With engine off, put transmission in first, turn front wheel one half turn in
forward direction. Have your helper shift the transmission to neutral while
you are underneath watching the transfer-reverse-shift-rod lever (on the
transfer case).
If this lever moved during the shift, the transfer-reverse-shift-rod should
be shortened by loosening jam nut and turning rod.
If the lever didn't move, it MAY be right (bad deal, 'cause then we go into
transfer), BUT more than likely the transfer-reverse-shift-rod needs to be
lengthened by turning out.
Do this until the lever on the transfer does not move during the
first-neutral shift, but ALMOST does.
Then repeat initial test, if it now passes you are good to go, if it fails
still, look at doing transfer case work.

BTW, I have documentary evidence that as early as 1953 Reo had developed the
air shift sprag, in response largely to one man's crusade against the
overrunning clutch. This issue was addressed by two high level military
panels, at least one of which favored the overrunning clutch.
BUT, Reo and members of the military also felt that the typical TM's of the
time (like TM 9-819) went into way too much detail for the operator (such as
describing the above procedure), which led to an excessive amount of
"tinkering" by those not qualified to, not only on the sprag, but MANY other
parts of the trucks too.
This resulted in a revision of the military's manual policy, and the moving
of many procedures into higher echelon manuals.

Hope this helps,
David Doyle



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