M939 series transfer case low range / front axle engagement

[70deuce]

webbk24 any chance you have some pics of that switch?

 

[Hoefler]

Here are pictures taken from the top (standing where spare tire sits) along with a shut off valve I installed in between air supply and transfer case interlock piston. I simply flipped the front axel engage switch flipper so it does not engage with the washer.
Pete

 

[Vintage iron]

This seems to become a more and more common issue. I need to do more research on this

 

[lindsey97]

just finished installing a 1/8" ball valve on my interlock piston. my installation is identical to hoefler's, and it works great.

I have a theory on shifting these trucks and it goes like this:

1) place truck in neutral, stop rolling, and shut off the engine.
2) leave parking brake disengaged, to allow some movement in the drivetrain.
3) shift the transfer case lever into neutral then into low range. start engine, place gear selector in gear and operate vehicle.

to go back into high range from low:

1) place transmission in neutral, shut off engine, and leave parking brake disengaged.
2) shift transfer case lever into neutral then into high range. some rolling or slight movement of the truck isn't a bad thing here to facilitate shifting.
3) if transfer case doesn't engage high range, start engine then shut off immediately while applying moderate pressure on the transfer case lever to engage high range. you may feel some clicking while applying pressure, but when the clicking stops the transfer case will engage high range. letting the truck roll forward very slowly will often complete the range shift.

why shut off the engine you ask even if the transmission is in neutral? when the engine is turning, it pumps and moves oil in the transmission, which causes rotation of the output shaft. so when this is occurring, and you are trying to shift the transfer case, and truck isn't moving,the gears in the transfer case are moving on the input side but cant
move on the output side thus not allowing the transfer case to complete the range change.

anyone that has grown up on a farm or been around heavy machinery can understand what I am saying. we have all seen a tractor at an idle sitting in neutral with the pto disengaged with no rear implement and the pto WILL be turning. a person could grab it and stop it( don't try it due to safety reasons)

all I am saying is that when I shift my truck's transfer case, I shut off the engine and let the truck roll ever so slightly while completing the range change.

and this above method of shifting applies to manual trans and automatics. I welcome your thoughts and comments.

 

[lindsey97]

also while performing these mods to your transfer case, now is the appropriate time to adjust and check your transfer case shift linkage travel. mine wasn't fully engaging high range on the shift barrel. this task is completed when removing the big flat washer on the end of the transfer case linkage when disconnecting the auto front axle actuator. my linkage was too short and after removing the large washer I lengthened it by going out 2 turns on the clevis that attaches to the transfer case shift barrel. a little adjustment here translates to a lot in the cab on the lever travel.

I bet there are more than a few m900' out there that would benefit from a linage travel check.

 

[162tcat]

Lindsey97,

There is no need to start and stop the engine as the 5 ton transfer case is synchronized unlike most civy vehicle's. It's actually much easier to shift while rolling. Turning the engine on and off is just wearing out your starter. If that's the only way it will shift then something is out of adjustment

 

[Vintage iron]

There is a measurement in the TM I just can't remember where it was?

 

[webbk24]

I didn't take any pictures but I will, if you remove the transmission shifter from the mount (4 7/16 bolts) its just inside, there are 3 wires that go to the shifter 1 is the light, 1 is the power in to the detent switch, the other is the wire from the detent switch back under the truck to the transfer case shifter button, Then to the solenoid that relieves the air pressure to the plunger. There are two wires from the solenoid 1 is the power wire and the other is the ground, I had one truck that lost the ground connection and would not shift.

 

[tashaak]

My front won't engage ,it did before no problem. The light does not go on,and does not lock. What valave are you guy's talking about and where is it. Pics would be very helpful with all the crap under these rigs. I thought it was water in the airlines but it isn't. Help Please

 

[tashaak]

Do these transfer case switches get stuck. Mine will not engage when I flip the switch on the dash. I can hear air coming out the vent instead,what would cause that. Should I give it a whack,the temps are warm now also.

 

[Floridianson]

My M925 is doing just what it should and I am not going to change anything. As said a better driver could get away with disconnecting the interlock and if you feel you need control of the front end engagement then do the air switch washer /tab thing. For the people having trouble shifting with the motor running and in netrual if the air lockout on the transfer case is working then don't forget to check the 5th gear lockup switch. If you ever pick up a truck and it stalls when you put it in gear then there might be a problem with the switch in the end of the transfer case lever sticking on and leaving the 5th gear lockup ingaged. In that case if you can 't get the button to release then disconnect the hot wire going to the 5th lockup.

Post # 9 buy Krwk545 tells the story.

 

[Jon Giovani]

just finished installing a 1/8" ball valve on my interlock piston. my installation is identical to hoefler's, and it works great.

I have a theory on shifting these trucks and it goes like this:

1) place truck in neutral, stop rolling, and shut off the engine.
2) leave parking brake disengaged, to allow some movement in the drivetrain.
3) shift the transfer case lever into neutral then into low range. start engine, place gear selector in gear and operate vehicle.

to go back into high range from low:

1) place transmission in neutral, shut off engine, and leave parking brake disengaged.
2) shift transfer case lever into neutral then into high range. some rolling or slight movement of the truck isn't a bad thing here to facilitate shifting.
3) if transfer case doesn't engage high range, start engine then shut off immediately while applying moderate pressure on the transfer case lever to engage high range. you may feel some clicking while applying pressure, but when the clicking stops the transfer case will engage high range. letting the truck roll forward very slowly will often complete the range shift.

why shut off the engine you ask even if the transmission is in neutral? when the engine is turning, it pumps and moves oil in the transmission, which causes rotation of the output shaft. so when this is occurring, and you are trying to shift the transfer case, and truck isn't moving,the gears in the transfer case are moving on the input side but cant
move on the output side thus not allowing the transfer case to complete the range change.

anyone that has grown up on a farm or been around heavy machinery can understand what I am saying. we have all seen a tractor at an idle sitting in neutral with the pto disengaged with no rear implement and the pto WILL be turning. a person could grab it and stop it( don't try it due to safety reasons)

all I am saying is that when I shift my truck's transfer case, I shut off the engine and let the truck roll ever so slightly while completing the range change.

and this above method of shifting applies to manual trans and automatics. I welcome your thoughts and comments.

That is exactly how I shifted mine right from the start. As ex military and a farm boy I found your logic on this impeccable.

 

[Floridianson]

I have a theory about these trucks. They were designed to be smarter than some of the drivers. If it don't do what it should, fix the problem and let them run.

 

[todds112]

Here are pictures taken from the top (standing where spare tire sits) along with a shut off valve I installed in between air supply and transfer case interlock piston. I simply flipped the front axel engage switch flipper so it does not engage with the washer.
Pete
View attachment 504430View attachment 504431

Just noticed today that mine was flipped by the Army, I didn't have to mess with it.

 

[idbankrman]

Anybody know where to get one of the little switches inside the transfer case handle? Its the switch the button in the handle pushes on. I have two that are bad, one from my dump truck and another from a scrap truck

 

[DemocracyEnaction]

Ok so humor me... the selector switch has IN and OUT. Which engages the front wheels?

 

[kennys@wi.rr.com]

In

 

[DemocracyEnaction]

Roger that ,thank you.

 

[Tonymac96]

You guys rock! That's a lot of info for a newbie and I really appreciate all the help. Love my trucks My new one is a 5 ton and I have a 61 404 unimog and a mule for fun.... Keep the wrenches turning boys.

 

[PapaPumpSD]

My M925A2 t-case gives us grief when trying to shift it. I'll try making sure the button on the t-case handle is working properly 1st then I'll check the linkage adjustment. If neither of those work, I'll try the interlock solenoid valve knock-out (page 1-35 on operator's manual).