M939 transfer case air lines installed wrong

I have some for sale in the classifieds. You can take off tank drain lines and pour alcohol into the tanks and it will circulate. I dont knoe about the antifreeze stuff. The tms dont reccommend anything but I have seen military mechanics using the alcohol.
Will

tashaak said:

You say you work on these for a living, cool. I have a recent problem since it turned cold. I cannot lock in the front drive it just keeps hissing air what sounds like it is coming from the stack where the vent lines go. The green light will not come on. I get it up to full pressure but it will not lock in. Is it a temperature issue. I never had a problem before when it was warmer. This is my first winter with the truck. I have an air dryer also. Is it common for this to happen. Thanks

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I had the same problem but it was regardless of the weather...turned out the engagement piston on the top rear of the transfer case (follow the air line from the low-range auto engagement switch mentioned at the start of this thread). It was filled with moisture (truck came from a very humid environment, air dryer was non-functional when I got it...since rebuilt) and the corrosion prevented operation. So when I flipped the front axle engagement switch, air pressure dropped & I could hear a hissing of air escaping into the intake stack. The front axle would not engage either.

TNJ Murray has a piston rebuild kit available on their website. I cleaned the corrosion off of mine, greased everything up & reinstalled it...now there is no air leakage & the front axle locks in perfectly.

It's possible that the moisture in this piston is frozen, preventing front axle engagement & bypassing air pressure into the intake stack.

Hey Rockafellar,

I noticed that my reply to the last question about the oil in your air and wondered if you got it or it went into the abyss. The air compressor is fed by the engines oil system, and if it pushed into the air system you would find it everywhere. gear oil is another thing.

Thanks, Bolkbich!
I am considering trading for an M-944 w/o its tool shop tools and turning it into my offroad farm tool truck. I will look at the lines and maybe jack up the front end and see if it is routed rightly thank to you. We appreciate your sharing.
Johnny Gregory
NC

Wow. Awesome thread. I tried my best to read each reply, but sometimes, I have to admit, my brain just can not catalog all the good points. So please forgive me if I ask a repeat question.

As I understand from this thread, those that do not want "auto engage" when going into low can remove the washer that activates the auto engage switch? Sounds like several have done this now, and since I do not need auto engage, I will remove the washers on my 931s. Unless someone has found this to not be the answer after all?

I shall test my front axle engage before I ask any about that, and the procedure has been outlined in this thread to lift the front tires off the ground, air up the truck, and rotate the wheels with the air switch IN and again with the switch OUT.
However, upon using one of my trucks friday (1-9-15) I did note when is a slippery situation off road, with the air switch IN, the front axle did not spin a tire when the rears were spinning. I did not get stuck, but learned I did not have front drive. Now after driving it for several hours, in both low and high range, on road and off road (pulling a farm sprayer) no real heat was observed built up in any gear box including the t-case. It was just barely warmer than the rear drivers.

But the air switch on the dash, when moving it from IN to OUT, only a very small bit of air is released. Like only the mount the switch itself can hold. There is no more air release anywhere in the system when moving the switch to OUT. Would this be another indication of the reversed air lines?

I searched the TMs and found a diagram of the air lines on the t-case, but recall a mention in this thread about a diagram somewhere being not correct. Which diagram is the correct one? The TM listed in the 939 series, or some other?

Thanks.

I think this thread should be sticky.

Beerslayer said:

Here you go Glen. Now how about getting a pallet under that top and getting a weight on it?

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Beerslayer, where did you get that diagram from, is there a software that had all the info on these trucks?

cobratodd said:

Where can I buy a new air valve? It appears as though my M923a2 valve is gray plastic, it is split, and is leaning air. (Or am I confused and not looking at the right part?). I tried searching the net but I must not be using the correct terminalogy for that part.

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If it is leaking air, doesn't matter what it is, it needs to be changed.

railroadmike said:

Hey Rockafellar,I noticed that my reply to the last question about the oil in your air and wondered if you got it or it went into the abyss. The air compressor is fed by the engines oil system, and if it pushed into the air system you would find it everywhere. gear oil is another thing.

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Railroadmike, Finally after almost two years I got around to actually trying to fix the issue again. I had temporary fixed it by running a vent line from the tcase oil fill hole. But yesterday I discovered that the Interlock Air Cylinder seal was leaking which was pressurizing the tcase. The pressurized tcase pushed gear oil backwards through the Front Wheel Drive Air Cylinder to the Front Axle Lock Switch. I believe the tcase vent line must also be plugged. I haven't had a chance to check today as it is pouring rain. Looks like 99nouns had the same problem. http://www.steelsoldiers.com/showth...fer-Case-Problem-SOLVED&p=1895695#post1895695

plode said:

I confirmed today that the front axle is locked on my truck. The auto engage switch with the wheel that normally hits the washer has zero effect when I move it by hand.

Can I just connect the front axle engage air line from the cab switch direct to the front axle cylinder on the back of the t-case, and plug off the air line from the PPV(and get rid of the wheeled switch entirely)?

I edited the picture below to illustrate what I'm asking.
View attachment 489409

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Did you do it? I am getting ready to, 2 years after you posted this

Actually removing the washer is easier than fabricating new connection.

I am sure it is. My valve is so corroded that it pisses air out of the top of it. Easier to cap off the constant pressure line at the 3 way union on the frame and run a new line from the dash switch to the T-case activation. Cleaner, too.

grendel said:

I am sure it is. My valve is so corroded that it pisses air out of the top of it.

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Of course I didnt know, yeah you are right.

ok. trying to learn here. why will the xfer case break in low 6x6 reverse, but not forward? it gets the same torque either direction correct?

Gear Ratio in the trans is different between 1st and reverse. 4.17 going forward in 1st, 10.76 ratio for reverse. You can use low range in the transfer with no problems as long as you are gentle on the go pedal. These trucks with the older 250 Cummins in stock form make 650 ft lbs. Multiply that by a factor of 10 without consideration of the torque converter doing it's own multiplication and pretty soon, something has to give if a wheel won't turn or the load is too heavy. The transfer is actually pretty tough on these trucks.

spectra3279 said:

ok. trying to learn here. why will the xfer case break in low 6x6 reverse, but not forward? it gets the same torque either direction correct?

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Sent from my SM-G935P using Tapatalk

Bought another one of these **** trucks again!!! It’s a bad addiction. ... anyways, it’s got the “Axle Lock In” flashing red red light on dash paired with the buzzer. Aside from the obvious, what’s going on here... I can’t get it to shut off(stop blinking and buzzing). I flip the front diff to “out” and I can hear the air bleed off but it’s not having any effect.

The flashing red light has nothing to do with Axle lock in, it seems like you have air build up problem or emergency brake problem, does the truck build air?

Yes sir. Both the primary and secondary are building and holding normal. I was not able to hear any leaky air lines.

The axle lock in has no pulse for its light to make it flash nor is its light ran thru the warning buzzer. . Your lights were just put back in the wrong socket. Means you have a bad air tank pressure switch.

So cheap unsafe fix to disconnect the buzzer and drive around with flashing lights which will be super annoying at night time just keep your eyes on air gauges to make sure you have more than 90psi and your hand brake is released.

Or find the air tank where that air pressure sensor is and change it. (Recommended)

Seller said the truck never use to have the buzzer and light on dash.... he said he thinks when he used the Hi-Low and park brake it stared and hasn’t turned off since ����*