M1078 Transmission inop

[Rage]

My transmission will not engage at all. The trouble code indicates that output shaft sensor. I be already checked the wiring harness and replaced the sensor and batteries. I now have a replacement TCU. I'm considering looking for a good used valvebody with solenoids to replace the ones inside the transmission it self. I'm ope to any help I'm completely lost and so are the mechanics at the CAT maintenance facility in Harrisburg. So I could really use some guidance.

 

[coachgeo]

My transmission will not engage at all. The trouble code indicates that output shaft sensor. I be already checked the wiring harness and replaced the sensor and batteries. I now have a replacement TCU. I'm considering looking for a good used valvebody with solenoids to replace the ones inside the transmission it self. I'm ope to any help I'm completely lost and so are the mechanics at the CAT maintenance facility in Harrisburg. So I could really use some guidance.

Is this an A0 or A1 truck? What year?

 

[Suprman]

Put the computer in. See what happens. If that doesn't fix the problem I would lean towards a harness issue before the trans pack itself. Harness is cheap trans pack is big bucks.

 

[NDT]

Read post 159 for Allison troubleshooting guide: http://www.steelsoldiers.com/showthread.php?152882-Working-on-the-M1078-LMTV/page16

Cat can't fix Allison issues, that has to be done by Allison.

 

[scottmandu]

I'm going to ask a silly question but do you have fluid in the transmission?

 

[parklandtrans]

From my years in the "Business " usually if it will flat out "not engage" ..it's usually not an electrical issue. When the engineers design these fluid mazes they have normally thought far enough ahead and incorporated fail safe modes in the design that "Does not remove the engagement into reverse or forward gear....if that electrical harness burned up they want you to be able to limp to a close safe zone.
A defective output speed sensor would not cause the transmission not to engage...period. I always set out problem solving by checking all the simple stuff...as someone stated earlier...is there fluid in the unit..?? A lot of professional techs have gotten bit by that one more once..!! So please check and double check, it doesn't cost anything to check and recheck.
Not knowing exactly how the transmission and cooler lines are set up but this is a real easy and a VERY ACCURATE CHECK TO SEE IF INTERNAL PROBLEM EXISTS. Remove the return line to the transmission and start engine.(of course this is after we have verified the fluid level is correct, please message me back asap if the fluid level is WAY overfilled and we will go another route) prior to starting engine you will want to put the line in a bucket of some type to collect the fluid. If you put the wrong end of the line in the bucket it will be apparent very quicky because fluid will come out of the end at transmission.
What we are trying to determine here is...is the fluid being moved via the pump..?? If there is absolutely NO flow at all we have an internal problem, possibly broken pump gear, stripped splines on T/C, etc etc...
Now, if there is fluid moving and you see it squirting out the line into the bucket, then we know we have a pump that at least has the ability to move fluid, and we will need to look elsewhere for cause and correction.

Please keep me abreast of our progress and message me or call with any questions or concerns...don't worry there hasn't been one out there that's beaten us yet..!!!

Bob Huke
Parkland Transmissions and Automotive Inc.
Tacoma, Wa
1-253-531-2622. Office
1-253-225-0441. Cell

 

[snowtrac nome]

a weak spot on the allisons are the rear clutch pack, every thing in the trans runs through them ,if some one got it stuck and tried to rock it you can rip the internal teeth out of the clutches, than you will have no forward or reverse. I dare you to ask how I know about this. you can have an assistant put it in gear and standing at the back of the transmission you should hear noise.

 

[parklandtrans]

Dear Snowtrac,
I gotta ask how you do know...??...I love hearing stuck stories from my other fellow soldiers....trust me I got a few of my own as well....you first..!!!
Outstanding technical advice in regards to the rear clutch pal Assy. Definitely listening for noise and for any fluid leaks in that area. I have seen the internal components fail and cause literally an "explosion "..inside and push components out thru the case Assy...allowing for a leak to develop.
Please keep me I the loop because I'm very curious....
Bob Huke
"The Trans Man"
.

 

[Rage]

It's a 1997 A0

 

[Rage]

For arguments sake I checked the fluid level all was good. But it did smell a little burnt which is odd since it was changed only a month ago (less than 500 miles).

 

[Rage]

I've got an Allison tech looking at it tomorrow so I'll update everyone. But he tends to believe the pump died.

 

[Rage]

The Allison transmission shop just called asking me if I knew where the output shaft sensor was. Any ideas I already replaced the sensor near the bell housing.

 

[Suprman]

Thats it

 

[Rage]

Allison Transmission Tech says my transmission need rebuilt. If anyone knows where I can get a good used transmission please let me know. Otherwise I'll have a good parts truck for sale.

 

[Suprman]

I have trans

 

[scottmandu]

Allison Transmission Tech says my transmission need rebuilt. If anyone knows where I can get a good used transmission please let me know. Otherwise I'll have a good parts truck for sale.

I've got a few from both the MTV and LMTV