M944a1 allison transmition question

[1z-bar]

I have been waiting on tires for my m944a1 {found some in PA. for 130.00 - picked up 4}. So i haden't drove it since it came off the flat bed. It shifted good before. I had played with my alternator/generator {25 KW} after i got it back, i'm going to have hit it with 12 volts to see if it will start working.
But any way i went to move it around and it won't go out of first gear. Tryed hi and low range {both shifted before} engaging and disengaging the pto but it still wont go out of first...... any ideas.
On a seprate note i have a air leak. after i shut it down I hear it through the air intake any one know where i can get a rebuild kit for the compreser the engine is a cummins 250.

 

[hemichallenger]

If your air compressor is leaking air after you shut it off take the big line off that goes to the tank after
you build up the air pressure. If keeps leaking out the line take the check valve apart
it should be at the tank were the line goes in. Air should only in not out of the tank through that line. You should be able to get any parts from
a cummins dealer if needed

 

[BKubu]

Your shifting problem could be related to the shift modulator. I don't know that this is the problem for certain, but I had a truck once that would not shift out of second gear and it was the shift modulator. Once that was replaced and the shift points were set, the transmission shifted perfectly.

 

[1z-bar]

I will check the line coming off of the air compresor and see if I can find the shift modulator, any one have a book or know what transmition they put on the 250 in 1986? Thanks I will keep every one informed.

 

[1z-bar]

I asked an allison teck abought the shift modulator he didn't think that was it {i think he wants paid for a service call } He's said he would call back tomorow.
Hears a pic of it opened up!

 

[Ord22]

1z-bar

nice batmobile! we nickname them when i was in the army. the doors represented batman as he lifted his arms up in the air.

 

[1z-bar]

The allison repair man is comming thursday 98.00 HR + mileage . He thinks it's the govener for the trans.

 

[hemichallenger]

When i refered about the air comming from the intake that was ment on how to check the air leak because i do not think it is your compressor. This has no conection to the trans problem. I do not know anything about allisons.

 

[1z-bar]

Thanks ted, I 'm going to check that as soon as I can. I'm just more woried abought the shifting problem. I would have checked it already but the truck is at my dads 30 miles away. Thanks for the info!!

 

[kc5mzd]

I don't know about your trans but I have seen some that use air to shift. I would try to make sure the air leak is not coming from anything that goes to or from the trans.

 

[reb87]

Your M944a1 has an Allison MT654CR transmission. It does not use air for shifting like the cat 7155 in the m920

 

[1z-bar]

Thanks Reb, I should have posted that earler {trans. MT654CR} . The air presure bilds up to 120 and stays their. It just takes 7 min or so to build up at idle and 2min to go to 0 after shuting off. I am going to try today to take the air line off if I have time. Thanks!

 

[halftrack]

If the truck has not been driven for long periods of time, it is common for water or moisture to settle out of the tranny fluid and sink to the bottom of the tranny. This in return causes slight corrosion in the valves that open and close to allow shifting from one gear to the next. It is most likely not servere corrosion but just enough to make the valve from 2nd to 3rd gear to stick or whatever gear it wont go into. The trucks like to be driven and sitting up is the worst thing for them. It is no big deal to un-stick the valve but you have to take the pan and the whole valve body down to get to it. If your mechanic skills are limited, DO NOT attempt to do it yourself.

 

[1z-bar]

I found out why it wouldn't shift from 1st into 2nd my rpm wasn't high enough I must have bumped my control on the dash. The rpm just wasn't high enough to shift. I feel abought this _ high Let alone the bill I got from allison repair man.... To the tune of 322.00 He did say every thing on the transmition looked good though. Oh did i foget to say.

 

[1z-bar]

I took the air line coming off the compressor today. Their's no check valve going to the air tanks so the air leaks right back through the compressor when it's shut down. Their is a presure relief popit going in to the first tank but no check valve. Any one know what kind of check valve I should put on?

 

[hemichallenger]

Most all heavy trucks with air brakes have a check valve that screws into the air tank at the feed line from the compressor unless it has an air dryer. You just need to see what size treads you have and should be able to get one at any heavy truck parts store. Napa. freightliner, truck pro, fleet pride, etc. It has to put on so the air flow is from the compressor to the tank or it will not let air to the tank.

 

[steelsoldiers]

Here are the most current wiring and compressed air diagrams for the 939-series trucks: https://www.absmodtrack.com/m939/uploads/SOMARPI 9-2320-272-24.pdf There are several check and double-check valves in the air supply lines that can stick and allow air to back flow through the compressor after you shut the truck off. ABSmodtrack.com is a great website for 939-series trucks. Spend some time on there and you will learn a lot about your truck.