M1078 Transmission Problem

coachgeo said:

check your flywheel bolts thru the port hole on bottom of bell housing

Click to expand...

Satchaser said:

Hello Friends.

I bought a 1995 M1078 from GovPlanet last year. 10k miles. Great truck, it ran right off the start. No leaks, everything seems to work except the CTIS which I think is just unplugged. I have put about 200 road miles on it, and as I said it performs perfectly. Engine starts instantly and runs smooth.

Last weekend I was on the road (paved) doing about 50 when I lost power, as if the truck went into neutral. Engine was fine, Transmission display seemed fine (but I was distracted getting off the road with no power). I shut down and restarted with no effect. I got lucky that I was only 1000 feet from home so a quick tow.

I read through the posts of SS and nothing seems to be right on target. I have modest mechanical skills. I physically inspected the transmission and nothing looked loose or out of place. No marks, no fluid marks, etc.

I checked the Tranny fluid levels, a bit low so I topped it up (15w40).

I have restarted the truck several times, it *feels* like the transmission is just not getting the command to shift into any gear (Reverse, Drive, Mode, etc.), all are non responsive. I should note that at startup the display looks normal. If I push D I get 7 2 displayed, but I do not feel the transmission engage, and if I push the accelerator the engine will rev up, but you feel no tension from the transmission. After a few changes of gear selection, the display will stop responding to change gear commands, however it will respond to commands such as 'show error log'. I can post a video if anyone thinks it will help.

I checked the codes on the Tranny display and here are the results:

D1 25 11 (Output speed sensor, detected at 0 output rpm, 1st)
D2 55 17 (Oncoming C3PS test (after shift), 1 to R)
D3 56 66 (Range verification ratio test, 6th)
D4 21 12 (Throttle position sensor, failed low)

I do not know how old some of these are, I can only verify that D1 25 11 is new (It was D2 the first time I looked at the log)

I am hoping one of you recognizes the issue or has a good recommendation for a mobile tranny mechanic in Sonoma County California.

Thanks and let me know what other information would be useful.

Click to expand...

Suprman said:

Output speed sensor is usually the engine output speed. Its a common failure item. Its a small inexpensive sensor on the bellhousing and held on by a small bolt. Maybe the connector just fell off. Or it could be a wiring harness issue. Take the grill off. The trans harness meets the cab drivers side on the hump. Look for dry cracked insulation coming off. You didnt recently pressure wash the truck? I also see low voltage issues causing trans problems. Lousy main ground I add one from the batt negative to the main frame rail? Water dripping down over time can get into transmission control components and cause issues.

Click to expand...

Allison 29536408 Transmission Speed Sensor

Check out the deal on Allison 29536408 Transmission Speed Sensor at XDP

www.xtremediesel.com

Satchaser said:

I did not recently pressure wash the truck or do anything else that would disturb the bottom. I did have an issue with two of the older batteries and they were low. This was just before the final drive. After the problem I did ensure that the batteries were fully charged, but I am suspicious of their quality. The two other batteries are just a few months old. The volt meter is in the green, and the engine has no hesitation to crank when starting.

Does anyone happen to have a link to the Output Speed Sensor that @Suprman mentions? Is it this?

Allison 29536408 Transmission Speed Sensor

Check out the deal on Allison 29536408 Transmission Speed Sensor at XDP

www.xtremediesel.com

Click to expand...

Satchaser said:

I did not recently pressure wash the truck or do anything else that would disturb the bottom. I did have an issue with two of the older batteries and they were low. This was just before the final drive. After the problem I did ensure that the batteries were fully charged, but I am suspicious of their quality. The two other batteries are just a few months old. The volt meter is in the green, and the engine has no hesitation to crank when starting.

Does anyone happen to have a link to the Output Speed Sensor that @Suprman mentions? Is it this?

Allison 29536408 Transmission Speed Sensor

Check out the deal on Allison 29536408 Transmission Speed Sensor at XDP

www.xtremediesel.com

Click to expand...

Skyhawk13205 said:

Take out your keypad/ecu then ring the runs for the turbine and output speed sensors for the correct range. If not in the range it should just be a sensor/wiring repair. For parts I suggest going to an Allison dealer, it may be the same price or a little more expensive but they should have the correct/updated parts. You can cross reference with the TM parts manual as well.

Click to expand...

Satchaser said:

I have visually inspected the wires and harness. Nothing looks stressed or warn. The sensors look unscathed and in good condition. I have not gotten to ohm'ing out all of the wires as suggested.

Two new ideas have arisen:
1) Once the engine is started, the transmission will not attempt to go into gear. Would the speed sensors really be relevant since the speed is at 0? If I rev the engine, while in gear, after a bit, I do get the 25 error. This makes me think that the sensors work as it is true the engine is spinning but nothing is coming out of the transmission.
2) A local mechanic, who is good with Cat's but admitted he knows little about Alison's mentioned the one thing he has seen is that the ECU(??) has a dedicated power lead from the batteries and if its not perfect problems happen. This struck a chord because prior to the problem I was monkeying with the batters to charge the older ones.

Here are my current questions.
1) Does the shift selector get its power from the ECU? Given that it lights up, does this mean that the ECU is getting power (perhaps voltage is low)?
2) Can anyone collaborate the dedicated battery power wire? I do not see one when I inspect my battery area.
3) What exactly causes the transmission to physically engage in forward or reverse gear? I wonder if that component has failed.

Thanks

Click to expand...

Satchaser said:

I have visually inspected the wires and harness. Nothing looks stressed or warn. The sensors look unscathed and in good condition. I have not gotten to ohm'ing out all of the wires as suggested.

Two new ideas have arisen:
1) Once the engine is started, the transmission will not attempt to go into gear. Would the speed sensors really be relevant since the speed is at 0? If I rev the engine, while in gear, after a bit, I do get the 25 error. This makes me think that the sensors work as it is true the engine is spinning but nothing is coming out of the transmission.
2) A local mechanic, who is good with Cat's but admitted he knows little about Alison's mentioned the one thing he has seen is that the ECU(??) has a dedicated power lead from the batteries and if its not perfect problems happen. This struck a chord because prior to the problem I was monkeying with the batters to charge the older ones.

Here are my current questions.
1) Does the shift selector get its power from the ECU? Given that it lights up, does this mean that the ECU is getting power (perhaps voltage is low)?
2) Can anyone collaborate the dedicated battery power wire? I do not see one when I inspect my battery area.
3) What exactly causes the transmission to physically engage in forward or reverse gear? I wonder if that component has failed.

Thanks

Click to expand...