I am in the midst of repairing a malfunctioning sprag unit on my M817 which has the T-138.
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I had to back up a hill, around a corner, fully loaded truck with a fully loaded M1061 trailer because of an oncoming truck.
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When I shifted to forward again the sprag stayed stuck in Reverse position. (that problem has been solved) As I pulled forward I felt it start to bind and hit the clutch and brake. At the same moment the sprag “Let Loose” the whole truck jumped with a terrible bang. I thought I blew the case up like the 939 series but it all appeared fine. I pulled on forward off the trail VERY slowly and no noises or anything unusual and gave it a good inspection. Pulled the hub caps on the front which allowed me to test the axle lock up. Both were good all the way to the transfer, but I could sometimes get the sprag to slip when in reverse. Drained some oil after a mile or so and it was perfectly clean, so I took it home. I expected to find something cracked but the only thing I can find wrong is that there are flat spots on outside of the sprag wedges/rollers which alters their width and in turn affects angle, allowing them them them to stack closer and creates extra space.
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I have a video clip of the sprag slipping with just hand pressure, but I don’t know how to post a video clip yet.
All that to say: Looking at how it all works in the 138 (I believe the 136 is the same) if it is locking up the front while rolling down the road it would have to be worn wedges or rough race not allowing it to free wheel.
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