Air shifted Sprag problems

[Nicholas]

I have been having issues with my M818 sprag. I hear an air sound when putting the transmission into 1st or Reverse. However, when I try to climb a dirt pile the front is not engaged. I was able to test the air cylinder with the shops air and it does shift. Any ideas or things to try. I did replace the air valve on the transmission and made a disconnect(M35A2 air valve on dash). Could that have any affect? Any help would be great. Thanks

 

[mhassett]

Sprag
does not have an air actuator.

 

[KsM715]

On the 5tons it does. There should be an adjustment procedure in the TM's.

 

[73m819]

Sprag
does not have an air actuator.

WRONG, the sprage is shifted by air for f/r. the air switch dumps the air, putting the sprag in neutral, no the air disconnect will not cause sprag problems, and trust me you CAN get stuck if you FORGET to flip the air on,

 

[Tow4]

You say you checked and the air cylinder shifts; can you hear the piston move when you move the shifter from neutral to reverse? There is a audible "clunk" when going into reverse.

+2 on check the TM.

 

[Nicholas]

I rebuilt the case and when the transfercase was out I tested it with shop air and you could hear a thunk when it went forward and reverse. In the truck you can hear air dump out of the valve when you shift from forward to reverse and vice versa, but no thunk of engagement of the sprag.

I looked in the TM section but could not find anything about adjusting the sprag. Where and what can be adjusted.

Also the air pressure had been reading about 90psi. I did adjust it up to around 100psi. Could that be an issue.

I pulled the 4 bolts and pulled the cylinder housing off. The seals are all new and it fits and moves with hand pressure sliding the housing back and forth on the shaft. (I did shine the housing before assembly and lubricate it with oil.) Not sure other than to pull the drive shaft and try to did deeper into the sprag.

 

[JH1]

It's also possible that the poppet valves on the tranny are fine, the air shift pneumatic ram is functioning and selecting the proper sprag, but the sprag itself may be bad. They consist of little tipping paddles that dig in, in one direction and slide past on the other. Typically, the forward going sprag fails first, because it is used more and also from historical use in Vietnam. Deuce and 5T were used to go from landing craft to beach head and in so doing, drove through sand, and due to slippage, the sprags engaged and got worn in the forward going side. If the little tilting paddles are not sharp, they don't dig in and transfer power. At least this is what I heard from a guy in a dark shadow in an alley, a long time ago.
Jim

 

[doghead]

Are your hoses on the wrong sides(reversed) of the air cylinder? This is also mentioned in the TM.

 

[Nicholas]

Got back to the working on the truck today, temp finally below 100+. I pulled off the front driveshaft and it was under tension. Now I can push and pull the sprag shaft in and out. When it is pulled to the forward position is it engaging the front or rear? Also what port on the poppet valve should go to the cylinder? ( I looked at the TM and mine are reversed compared to the pics, but the same as before disassembly). The sprag now seems to work when I push it in I can turn it one way but not the other. Thanks for the help.