925a2 not shifting past 3rd

[5tonman1971]

My 925a2 will not shift by its self past 3rd gear. I have to let off the throttle to get it to shift past 3rd gear. When I finally get it in to 5th it won't go over 45 mph and no it's not in 6 wheel drive. My rpms never seem to go over 2k but I know it should go to 2200 rpm.

The fluid seems to be at the appropriate level now at the full cold mark. But the truck is still doing it. I'm worried to drive it long enough to get the trans to full temp incase something is wrong.

Any suggestions?

 

[MtnSnow]

Could be your transmission linkage is out of adjustment

 

[1 Patriot-of-many]

Are you sure it's actually shifting to 5th? I thought mine was shifting to 5th but someone pointed out it's 4th gear running at 2200rpm @ 52mph. Mine is the same whether I have it in 1-4 or 1-5 so they were right. My linkage is fine. The TM's merely say if it's in the neutral position and it starts it's adjusted. If someone has something other than that please let us know. If you find out what the problem is please let me know and I'll do vice versa. I'm about ready to take my wrecker to an Allison shop.
Edit: Two of the closest heavy truck places including an Allison dealer said go somewhere else, they couldn't work on it, too old!

A couple things to check if I can figure out what and where some of them are. I know I need to adjust the modulator cable.
http://allisonparts.net/Allison-Transmission-Parts-A.html

 

[5tonman1971]

Are you sure it's actually shifting to 5th? I thought mine was shifting to 5th but someone pointed out it's 4th gear running at 2200rpm @ 52mph. Mine is the same whether I have it in 1-4 or 1-5 so they were right. My linkage is fine. The TM's merely say if it's in the neutral position and it starts it's adjusted. If someone has something other than that please let us know. If you find out what the problem is please let me know and I'll do vice versa. I'm about ready to take my wrecker to an Allison shop.
Edit: Two of the closest heavy truck places including an Allison dealer said go somewhere else, they couldn't work on it, too old!

A couple things to check if I can figure out what and where some of them are. I know I need to adjust the modulator cable.
http://allisonparts.net/Allison-Transmission-Parts-A.html

well I've been told that my shift modulator has gone bad and needs replaced and I heard that setting the shift points are a nightmare and is recommended to have an Allison dealer do it.

I'm pretty sure I'm counting 5 gear changes I confirmed this by start in 1-3 then moving to 1-4 then 1-5. I also can't get my rpms over 2000 rpms not surf if the gauge is faulty or I need to adjust my throttle linkage. I'm going to try the throttle linkage first and then see what happens from there. I'm also only maxing out at 45 mph in 5th gear that's what kind of really concerns me but in 5th I'm only at 1950 rpms so maybe 250 more rpms will make the difference

 

[5tonman1971]

Update

UPDATE:

I manually move the throttle lever on the injection pump and had soldier B watch the gauge and it still only hit 2000 rpms at full throttle is there a way to adjust this to gain the few hundred more rpms that I need? Is there a bad spring in the governor?

 

[Scott88M]

My M923A2 was doing something similar. I had to do alot of adjusting of the accelerator linkage not the transmission modulator cable.

If you look at the pivot point where the far end of linkage is, nearest the pump, the bracket with 2 small bolts holding it on was maybe a 1/4" out of alignment. That got me shifting without having to lift foot. Can't help with it not going into 5th.

 

[1 Patriot-of-many]

well I've been told that my shift modulator has gone bad and needs replaced and I heard that setting the shift points are a nightmare and is recommended to have an Allison dealer do it.

I'm pretty sure I'm counting 5 gear changes I confirmed this by start in 1-3 then moving to 1-4 then 1-5. I also can't get my rpms over 2000 rpms not surf if the gauge is faulty or I need to adjust my throttle linkage. I'm going to try the throttle linkage first and then see what happens from there. I'm also only maxing out at 45 mph in 5th gear that's what kind of really concerns me but in 5th I'm only at 1950 rpms so maybe 250 more rpms will make the difference

Also counted the shifts, Someone pointed out there are more than 5 what seems like shifts, converter locking up feels like one. If you are only going 45 you're in 4th. Mine at 2200 was about 52. When I put the selector in 1-4 I was counting the same amount of shifts as when I had it in 1-5.

 

[5tonman1971]

UPDATE: yes I was counting the converter lock up as a shift the only gear I have to lift for now is 3 after the converter locks up then I can use the shift lever to get in to 4th and 5th while getting to a top speed of 58 mph. I still need to tweak the shift modulator to get it to do it on its own and adjust the governer to get my rpms up to 2200

 

[Carlo]

well I've been told that my shift modulator has gone bad and needs replaced and I heard that setting the shift points are a nightmare and is recommended to have an Allison dealer do it.

I'm pretty sure I'm counting 5 gear changes I confirmed this by start in 1-3 then moving to 1-4 then 1-5. I also can't get my rpms over 2000 rpms not surf if the gauge is faulty or I need to adjust my throttle linkage. I'm going to try the throttle linkage first and then see what happens from there. I'm also only maxing out at 45 mph in 5th gear that's what kind of really concerns me but in 5th I'm only at 1950 rpms so maybe 250 more rpms will make the difference

You can adjust the shifts points with the cable by the accelerator cable on the cam / injection pump.

 

[74M35A2]

As a reference, my M925A2 is at 65-67mph @ 2200rpm, pedal on the floor. No mods yet. You should be able to achieve the same. The shift points and governed RPM are close together, so that makes it a little difficult to clearly see which is the culprit. Check your max RPM in neutral, you should be able to reach 2300rpm.

If your accel and trans linkage is adjusted correctly, your engine may not be making enough power to get there. Start with the basics such as air and fuel filters.

 

[5tonman1971]

As a reference, my M925A2 is at 65-67mph @ 2200rpm, pedal on the floor. No mods yet. You should be able to achieve the same. The shift points and governed RPM are close together, so that makes it a little difficult to clearly see which is the culprit. Check your max RPM in neutral, you should be able to reach 2300rpm.

If your accel and trans linkage is adjusted correctly, your engine may not be making enough power to get there. Start with the basics such as air and fuel filters.

I have completely serviced the truck new filters all around, and in nuteral I'm still only hitting 2000 rpms so I'm sure. Need to adjust the governer.

 

[Scott88M]

It might just be your accelerator linkage is way out of wack like mine was. Mine wouldn't shift without letting of gas pedal. I adjusted the shift modulator and it wouldn't even get out of first it didn't Rev high enough.

 

[5tonman1971]

How did you adjust the shift modulator?

 

[Carlo]

If you look at the pump you see to cables. One for the accelerator and the other for the trans. On the trans you see you can adjust it. There should be play in the trans cable. About 25mm from where the accelerator starts pulling it. If you don't have play the trans will not shift well with out lifting of the pedal. Also changing to dex3 oil smooths the shifts allot.

 

[Scott88M]

When looking at the accelerator linkage near the injector pump the modulator is connected to it you can see it snake down towards tranny. loosen the screw that connects it to the linkage and slide cable forward or back it only goes about 2-3 inches in either direction forward towards front bumper smoothes out shifts and helped mine shift into 3rd without having to let off the pedal. I slid it to the rear and it wouldn't hit enough rpm to make it shift out of first.

Also where the whole assembly bolts to pump mine needed to be adjusted 1/4" forward and made a night and day improvement in my tranny and accelerator. I can try to add pics if you need me to.

 

[5tonman1971]

Yes that's what I did to mine and I got my rpms up to 2300 but I still have to lift to shift past 3rd I'm thinking I just need to change the internal filter as I've already changed the external one. I'm considering taking it to and Allison approved truck shop to have the fluid changed over to dexIII

 

[5tonman1971]

Here's a few pictures

 

[Artisan]

If all else fails the FIRST place I would send my ALLISON Tranny to
is Precision Allison Transmissions in Upland , CA . There old school, they
have a dyno and they care...

 

[Scott88M]

I'll post a pic later today of where I had to adjust the whole assembly. That is ultimately what made the biggest difference on mine. It didnt even seem like it would be enough of a tweek to change anything but it did. I think that one tiny adjustment might be just what you need because it sounds like we had almost the exact same problem.

 

[Carlo]

I had a m931A1 that shifted hard up and down and I mean HARD. I adjusted most of this problem out but I also went to Dex3 and she shifted smooth. I few turns on the rod/cable makes big differences. Don't go to much at one time.