M939 Transfercase shifting

[73m819]

Can anyone point me in the direction of the correct TM for the teardown of a transfer case ? Thanks

tm9-2320-272-34-1/ 34p-1 (parts)

 

[engineer233]

Thanks I will look it over.

 

[Artisan]

Be sure to do a pictorial on that M939 series T/C rebuild there engineer233 ! ("Please")

 

[engineer233]

Sure will.

 

[Csm Davis]

Just a slight correction to this GREAT write up, Thank You, The correction is this, the 939 transfer case HAS a synchro for the H/L shaft, that being said and these transfers can shift on the fly, it is a lot better to treat it as a NON synchro, come to a stop to shift transfer, it WILL last a lot longer (shifting on the fly is really hard on it and not really designed for it).

Actually Ron the guys that drove these every day have told me and I have tried it they shift better if they are rolling, not really fast but rolling.

Just a slight correction to this GREAT write up, Thank You, The correction is this, the 939 transfer case HAS a synchro for the H/L shaft, that being said and these transfers can shift on the fly, it is a lot better to treat it as a NON synchro, come to a stop to shift transfer, it WILL last a lot longer (shifting on the fly is really hard on it and not really designed for it).

 

[panzerwillie]

Can anybody post a picture of the air actuator that needs to be by pass
thank you

 

[TexAndy]

Great thread. I think this is what is wrong with my 923a2 t-case shifting problem.

I've noticed that when I turn the engine off and let the air out of the system a few pounds at a time, it gets progressively easier to operate the transfer case lever.

Also, with the engine off, air system pressurized, battery switch set to on, you can't hear anything happen when you press the button on the t-case lever. I think the transfer case interlock valve ya'll have been talking about here isn't working properly.

I think I will just disconnect it and cap the air line. High range is all the way on the floor, anyways so it's not like there's a risk of it slipping into neutral on me going down the highway.

FYI guys, the big 4 volume TM has a diagram with instructions on how to replace the interlock valve being discussed. 9-2320-272-24-1. Starting at page 3-392

 

[mcmullag]

just for entertainment.....I was trying to disable the front axle engagement washer on the linkage and the truck apparently moved while I had the linkage undone. it is stuck in neutral and we dragged it forward while trying to push the shaft back into the transfer case for high range. could not get it the shaft to budge even with engine running and moving truck forward. got ahold of a truck mechanic who worked on these in the Army. He said sometimes trucks got stuck in low when they came out of the field and the pushed the truck backwards and got it to go into high range or they jacked up the front axle and turned the front tires while somebody pushed the shaft in to the transfer case. he got under the truck and moved the air switch lever that the washer moves and that causes something to clunk in the transfer case, I was turning one of the front tires while the front axle was jacked up and it clunked into low range. all I am saying is jacking up the front axle so front tires are off the ground, get the air up and play with that switch the washer moves helps to move that shaft in and out of the transfer case.

 

[acme66]

I also removed the linkage and pulled that washer off. Helps me a lot but I will sure take a look at that lockout because sometimes mine is a brutal beast (see picture below) and sometimes it is smooth like butter...

Video of removing it:
https://www.youtube.com/watch?v=jxbu8CVUUrk

 

[rebelqwes87]

So the general consensus is that the front axle being engaged while in reverse low is what causes the damage to the T-case?

 

[engineer233]

Engaged,low range, and in reverse.

 

[brazengoat06]

I learned the hard way that you NEVER attempt a transfer case shift while sitting in sand.

 

[Csm Davis]

I learned the hard way that you NEVER attempt a transfer case shift while sitting in sand.

Okay I will bite, why?

 

[brazengoat06]

If your TC gets hung between gears there's physically no way to rock your 5 ton to slip your shifter into gear. I believe this was being discussed earlier in the thread.

 

[Csm Davis]

If your TC gets hung between gears there's physically no way to rock your 5 ton to slip your shifter into gear. I believe this was being discussed earlier in the thread.

You don't have to make the truck actually rock back and forth, you can just push gently on the transfer case shifter as you just bump it into drive or reverse, and then right back to neutral. This is if the lockout is working properly a lot of guys think the transfer case is hung up between gears when the lockout is actually not operating properly.

 

[brazengoat06]

My lockout works properly. So if I'm understanding you correctly one should hold the lever towards the gear selection they desire as they place the shifter into drive and the TC shifter will fall into place?

 

[MtnSnow]

Yep