5 ton Transfer Case Ops

[Cdub]

Just checking a few things over on the M925 and found that the t-case doesn't seem to want to go into neutral or low by pressing the button and pulling up on the leaver.

I started going through the manual -24 and found that there is and electric air valve called a " Transfer Case Interlock Valve " and a air actuator called a " Transfer Case Interlock Air Cylinder ".

While scoping things over I found one of the wires on the Transfer Case Interlock Valve disconnected. I reconnected it, hit the batter ON, and aired up the air system (with out the truck running). The Interlock valve seemed to be working properly and sending air to the Interlock Air Cylinder. I'm not sure if the piston that is controlled by the Interlock Air Cylinder is working properly.


What is the main function of the Transfer Case Interlock Valve and Interlock Air Cylinder...?? Are these some sort of fail safe.......??

Thanks,

C'dub

 

[TacticalTruck]

It's been a while but I had the same problem with my M931. I think the interlock is a safety device which makes you put the tranny in neutral before shifting to low range. I can look it up tomorrow.
Jeff

 

[Cdub]

Well after giving it some thought. I think the electric system checks out with the Interlock Valve working and sending air to the Interlock Air Cylinder. Now all I have to do is make sure that the pistion with in the Interlock Air Cylinder is not frozen or hung up. It should be able to move freely with the air supply from the Interlock Valve to release the rod and change from High, Netural, and Low.....

This is what I've found so far........

 

[Jones]

The interlock/shift system does two things; not sure which one would be most important on the list. One, it keeps you from shifting the transfer case on-the-fly 'cause the ratios are far enough apart to cause damage. Two, it locks the transfer case in which ever position is selected so it can't be bumped into or out of gear.
The system also gives you front wheel drive only when you're in low range FWIW.

 

[Cdub]

Thanks Jones, that is a couple of things that I haven't thought of.......The interlock/shift system also does not allow you to shift if you are not in neutral as well.

What tests can be performed on the Interlock Air Cylinder to see if it's working the way it should with out removing it from the Tcase....??

 

[Jones]

To test the air cylinder itself you just need to remove the air line and apply shop air to air it up and see if you can shift the t-case lever through high range, neutral and low range. If you can't then the lock pin is down and in position. Next, remove the air supply and repeat the test; if you CAN move the shifter through the positions then it's working right. If you CAN"T then either the air cylinder piston or the lock pin is sticking.
Removing the air cylinder just involves unscrewing it from the t-case but you might want to measure the gap between the t-case surface and the bottom of the air cylinder just to make sure it gets back in to the right depth. With it in your hot little hands, see if the piston moves by pushing it down with a small screwdriver, punch or piece of rod stock through the air fitting hole. Since it has a sealing ring it should move but with a little bit of resistance and rebound on it's own because of a return spring inside. If it doesn't move, take it apart; removing the piston and return spring and clean out any gunk and re-assemble with a LIGHT coat of silicone grease (you can get little packs of the stuff from the auto supply marketed as distributor point cam grease-- it does a good job and doesn't seem to want to turn into cottage cheese when exposed to any moisture lurking in the air system). If the return spring is broken the piston won't move back to allow the pin to relax it's position in the shifter shaft groove. Re-assemble the air cylinder and check it by airing it up then dumping the air; the piston should move down then back off.
Before re-installing the air cylinder in the t-case, remove the lock pin and check the end for burrs to make sure it isn't sticking in the groove. Buff or sand out any you find. It should look like the pin in your illustration with a rounded nose on the end that engages the shifter shaft grooves; if it comes out with the nose chewed up, or broken, then make sure you fish out all of it and replace it with a good one.
LEGAL DISCLAIMER: This is all from memory so you should refer to the TM to verify. And; Free advice is worth what you paid for it.

 

[acetomatoco]

take me back to the old days... one lever, shift on the fly, double clutch no electronics, all new stuff is too complicated and break prone.

 

[TacticalTruck]

Re: RE: 5 ton Transfer Case Ops

take me back to the old days... one lever, shift on the fly, double clutch no electronics, all new stuff is too complicated and break prone.

You're showing your age RAM...those late model M939s came out, what, almost 25 years ago? If I still had my M931 I'd be able to put antique plates on it next year.

Jeff

 

[Cdub]

RE: Re: RE: 5 ton Transfer Case Ops

Thanks Jones, I'll check it out and let you know how I make out...........

Thanks a bunch,

C'dub

 

[Cdub]

RE: Re: RE: 5 ton Transfer Case Ops

I did a little road test today and even with connecting the wire to the Transfer Case Interlock Valve it didn't make a difference from the tests I did when I aired up the air system and turned on the battery. I still think that the problem does involve the Transfer Case Interlock Air Cylinder. I'll take it apart tomorrow and I'll let ya know how it turns out...........

Cheers,

C'dub

 

[Cdub]

RE: Re: RE: 5 ton Transfer Case Ops

It was a SUCCESS..............!!!!!

this is how things un-folded

-drained all air
-removed e-brake bracket as per TM
-disconnected air supply
-checked height of air cylinder to Tcase
and it looked like it was bottomed out
-removed air cylinder
-pulled out push rod
-removed air fittings from air cylinder

I started taking apart the cylinder four attachment bolts and a small little pile of rust fell out and the top of cylinder casing was all rusty. The spring was in good condition but rusty as well. I removed the bottom half and it was just as bad. Now I have the piston completely rusted in the cylinder. I started soaking the piston from both ends and using a large socket with a hammer started tapping it in both direction and more and more soaking. Finally it moved a little more and more until the piston was free from the cylinder. It was so rusty that I could hardly see the Oring around the piston. Thank goodness that Oring was still in good shape. Now the big clean up.

The assembly went well all back together. I couldn't understand if the air comes in from the top and the spring is also pushing the piston down. How the heck is the rod suppose to move...??? The piston moved freely like new with the old Oring and some lube spray.

It went back together very well. There was no sign of any wear what so ever on the end of the push rod. I don't think they ever used it sense the wire to the Interlocking Valve was disconnected and the Air cylinder started to get so rusty.

For those interested the Interlock works as a fail safe to be in neutral and also to hole it in the Tcase setting.

The electric end of it makes sure the trans is in netural or it won't allow the Interlock air valve to open. When the Interlock valve opens it shuts down the air supply to the Interlock Air Cylinder allowing the rod to move only under spring pressure which will keep tension on the Tcase rod. The Interlock Air Cylinder is under constant pressure pushing down on the cylinder piston keeping the Tcase from jumping in or out of gear. When the electric is supplied to the Interlock Air valve to cut the air off and allowing the push rod to move freely.

The Tcase can be move out of gear with no power but all air must be drained first before it can be shifted to take the pressure off of the Interlock Air Cylinder. This way if the truck is dead on the side of the road the Tcase can still be shifted.

The air valve for the front axle works very well when the Tcase is shifted into Low range and releases when taken out of Low.

Thanks for your help Jones........

C'dub

 

[Jones]

RE: Re: RE: 5 ton Transfer Case Ops

You betcha-- that's what we're here for.
Glad the operation was a success.

 

[Cdub]

Re: RE: Re: RE: 5 ton Transfer Case Ops

You betcha-- that's what we're here for.
Glad the operation was a success.

I owe ya a or two or three.....

One thing I couldn't figure out until it was assembled that the cylinder piston is released when the air is released. The way it stays in gear is that it has constant air on the piston pushing the rod down. Seems to make sense if you were disabled you could still put the Tcase in neutral and tow or recover the vehicle.

Wow have I learned a lot about the Interlock Air System for the Tcase.

Well I guess if it's not broken I can't fix it.....and what kind of fun would that be....

Now it's time to play in LOW range.....Hehehehe

Cheers,

C'dub

 

[acetomatoco]

RE: Re: RE: Re: RE: 5 ton Transfer Case Ops

Did the same operation on a M911 one time.. weird truck is in front wheel drive most of the time and the xfer shifts in the rears off road...easy to break if you forget to release the trailer brakes when loaded...Detroits can torque break most anything..

 

[No.2Diesel]

RE: Re: RE: Re: RE: 5 ton Transfer Case Ops

Does that mean I should add your name back on the RC sign up sheet?