M939-A2 Series M927-A2 Driving Question

[99nouns]

I have a question about driving experience on M939-A2 Series with Turbo.

I have a M927-A2 and there are some things might be abnormal, but since I never driven another one I am not sure, perhaps some one with experience can advise me. Also RPM shift points has changed since I bought it to higher RPM.

1- When I put shifter in 1-5 gear and start driving it doesnt shift full automatic, except 1st to 2nd gear. It shift what I call semi-auto, which I have to release the gas pedal to shift the gear otherwise it doesnt shift even I got to 2000RPM is that nomal?
Shifting goes as following.

Before 1st to 2nd 1600RPM at 10MPH Auto
Now 1st to 2nd 1800RPM at 10MPH Auto

Before 2nd to 3rd 1600RPM at 20MPH Semi Auto
Now 2nd to 3rd 1900RPM at 20 MPH Semi Auto

3rd to 4th and 4th to 5th goes the same semi-auto as the 2nd to 3rd at every 10MPH (like 30mph 3rd to 4th and 40mph 4th to 5th) but I use to get 50mph at 5th at 1500RPM now I get 45 at 1500 rpm and can only get to 60mph at 2100RPM full turbo hissing like tornado leaving a trace of black cloud behind.

If you guys can advise me what sounds right I would appreciate it.

Thank you,

 

[Scar59]

Transmission modulator cable may be sticking, attaches to the throttle linkage and left side of transmission. Disconnect, lube up, and ensure it is not bidding.
-report back.

 

[mikey]

Have you don't anything to the transmission since owning it, including changing the fluids?

 

[99nouns]

Transmission modulator cable may be sticking, attaches to the throttle linkage and left side of transmission. Disconnect, lube up, and ensure it is not bidding.
-report back.

Ok I will do that asap, thank you for fast response.

Have you don't anything to the transmission since owning it, including changing the fluids?

I have checked the Transmission fluid and it is clear as honey, and overfilled.

 

[brasco]

I had an issue with hard downshifts on my M923A2. It would also go all the way to 2100 RPM before shifting even under light load. I always had to modulate the throttle to get a good shift under light acceleration.

I could not find any issues with my modulator or cable but bought a new one anyway. This solved all my shift issues - it fixed the hard downshift and the truck now makes proper upshifts. See details in link below....

http://www.steelsoldiers.com/showthread.php?129882-M939A2-Transmision-Modulataor-Valve-Part-Number

I hope this helps.

Don

 

[99nouns]

I had an issue with hard downshifts on my M923A2. It would also go all the way to 2100 RPM before shifting even under light load. I always had to modulate the throttle to get a good shift under light acceleration.

I could not find any issues with my modulator or cable but bought a new one anyway. This solved all my shift issues - it fixed the hard downshift and the truck now makes proper upshifts. See details in link below....

http://www.steelsoldiers.com/showthread.php?129882-M939A2-Transmision-Modulataor-Valve-Part-Number

I hope this helps.

Don

Yes I do have hard shift as whole truck just hops specially 2nd to 1st

 

[brasco]

I would say make the adjustments per the TM and if that doesn't fix it then get a new cable. ( I think I have about .25" of slack in the moudulator cable at WOT- probably a little more than needed.)
I wasted a lot of time working with a modulator assembly that appreared OK but wasn't working right. If/when you pull out the old modulator be prepared for about 2-3 gallons of transmission fluid to come out. Also, make sure that you don't over torque the bolt holding it on.

 

[99nouns]

I would say make the adjustments per the TM and if that doesn't fix it then get a new cable. ( I think I have about .25" of slack in the moudulator cable at WOT- probably a little more than needed.)
I wasted a lot of time working with a modulator assembly that appreared OK but wasn't working right. If/when you pull out the old modulator be prepared for about 2-3 gallons of transmission fluid to come out. Also, make sure that you don't over torque the bolt holding it on.

Are you able to refer a page number please?

 

[Gunzy]

I feel the 2 to 1 hard downshift is somewhat normal. I agree with the others in checking the modulator cable for binding and proper adjustment.

 

[brasco]

See
TM 9-2320-272-24-1

3-145. TRANSMISSION MODULATOR AND CABLE MAINTENANCE
Page 3-398

 

[brasco]

I feel the 2 to 1 hard downshift is somewhat normal. I agree with the others in checking the modulator cable for binding and proper adjustment.

Gunzy,
I used to think that hard downshifts were normal. My first truck, an M923A2, was brutal on the 2-1 downshift. My second truck was really smooth on on the 2-1 downshift and all the upshifts were much more civilized as well. I just thought that I was lucky and won a good shifting truck. I then bought a M931A2 and it was smooth on the shifts as well. That's when I really started to dig into the modulator cable as the issue.

I was able to fix the hard shifts downshifts on the M923A2 with a new cable -it was a night and day difference. I just want to make others aware that they don't need to live with a brutal 2nd to 1st dowshift. For me, it was worth the cost to at least try and it worked for my truck.

Don

 

[99nouns]

I am gonna study the TM and work it tomorrow, thank to all those answered,

....to be continued

 

[dawico]

Reading this makes me want to work on mine also when I get home. 2 to 1 is rough but all the other shifting seems "normal".

 

[Scar59]

-follow the TM -24-1 installation/adjustment procedure, should fix the issue, if not R&R the cable assembly and adjust.

 

[MuleMac01]

LOL I'm having the same issue but I can't find a new cable tried adjusting it but no go. anyone know a source for one? tried searching the parts and NSN numbers that didn't turn up much.

 

[brasco]

LOL I'm having the same issue but I can't find a new cable tried adjusting it but no go. anyone know a source for one? tried searching the parts and NSN numbers that didn't turn up much.

Yes...
Go to link earlier in this thread (post #5) for full discussion on my search. I found a supplier https://www.cccables.com/Controls/Modulator.aspx

Part number 2230-54 is what you need. Check it out. It worked for my truck but, obviously, I can't guarantee just a new cable will solve the problem for everyone but it is a cheaper place to start than installing a new transmission.

 

[MuleMac01]

Yes...
Go to link earlier in this thread (post #5) for full discussion on my search. I found a supplier https://www.cccables.com/Controls/Modulator.aspx

Part number 2230-54 is what you need. Check it out. It worked for my truck but, obviously, I can't guarantee just a new cable will solve the problem for everyone but it is a cheaper place to start than installing a new transmission.

Thank you didn't know if they where the right kind.

 

[1 Patriot-of-many]

I looked at the TM for adjusting it, I think it's one of those I can't figure the TM out deals myself.

 

[99nouns]

I looked at the TM for adjusting it, I think it's one of those I can't figure the TM out deals myself.

Ok it rained and was cold last few days and I just looked at the truck and see that my model is different than the TM. Perhaps can someone describe the operation of that mod cable, is it supposed to be all the way at the end and tight?

 

[mikey]

Not to send you in a different direction, but some people have mentioned on here that they resolved the hard shifting problem, especially 2 to 1, by switching to ATF. I personally prefer to use what came in my truck and I've read there is risk of damage to the tranny if you do the switch wrong.

In post #4 you say it is overfilled. Did you mean "not" overfilled? Overfilling can cause damage and probably cause hard shifting. I had problems getting a good reading on the trans fluid level until I posted a thread here and got some great advice. Are you checking it correctly, at idle with trans at running temp? Have you added any trans oil since you've owned it? I know my deuce loves sae30 but the Allison calls for sae10.

Mikey