M931A2 Not shifting past 3rd

[dfletcher12]

I've got a 1991 M931A2 that now will not shift past 3rd gear. I've tried to manually shift it, accelerating slow, letting off pedal, it just won't release into 4th. It shifts just fine 1, 2 and 3. Can anyone help?
Thanks in advance.

 

[GasTurbineTech]

Is this a new to you truck? I just got a M931A2 in the late fall. Took a while to get the title and finally took it for its first few drives the last few weeks. Mine didn't seem to want to shift either. I was told give it more throttle, not the let off way like a car. Worked for me, more throttle made it shift much better.

 

[dfletcher12]

I've had it for 2 years. I've tried more throttle too, as much as it will take. I'm thinking that possibly the linkage needs to be adjusted to lower the shift points?

 

[GasTurbineTech]

Does this thread help: http://www.steelsoldiers.com/showthread.php?143547-M923-shift-point

 

[Suprman]

Did you check the fluid level? In neutral running while warm. There is a fluid pressure adjustment. Like a kickdown cable. Its connected to the throttle. Unless its disconnected I dont think its your issue though. After you check the fluid does it look good? If the fluid is dirty or burnt smelling its time for trans service. Alot of stuff is simple repairs the Allison dealer can do from the pan. They really are reliable transmissions.

 

[dfletcher12]

I adjusted the cable this weekend. It changed the shift points of gears 1, 2 and 3. Still will not shift into 4th.

 

[Suprman]

Did you check the fluid first? Was the level correct and how did it look/smell?

 

[dfletcher12]

That was the very first thing I did a week ago when I started trouble shooting. It looked and smelled normal. Level was a little on the low end, but still within normal range.

 

[MtnSnow]

What road speeds are you doing & at what RPMs?

 

[Suprman]

If the fluid is fine and everything else appears in order, I would do a service on the trans. Replace pan and spin on filter. Having the Allison dealer do the service may be a good idea. There are replaceable parts when they drop the pan to change the filter.

 

[dfletcher12]

3rd gear gets up to 39-40 at 2000-2100 rpm

 

[dfletcher12]

Thanks, that's going to have to be my next step.

 

[MtnSnow]

3rd gear gets up to 39-40 at 2000-2100 rpm

Ok. with those road speeds & RPM's yes it should be moving on to the next gear.

 

[quickfarms]

What is your governed RPM.

This will determine where the shift points are supposed to be.

After the truck is up to operating temperature. This is the beginning of the allison road test. Place the transmission in neutral with parking brake set. Put the throttle to the floor and hold for 15 seconds. What does the tach read?