First Post - new to me M1078 MD3070PT with Shifting Problems

[Suprman]

Check that harness. Follow along the drivers side frame rail and over to the trans. Check the trans mating connector its about a foot off the trans pigtail. Check the tps branch off. I have seen bad harnesses.

 

[isaacnasar]

OK - checked all the harnesses as supermn recommended - no visible issues. I'm leaning towards the turbine output sensor that is in the trans itself. An earlier poster mentioned the harness or the sensor going bad and needing to drop the pan.

The code from the WTEC from day one was listing a fault with the turbine output sensor - it's a pain in the rear but I think I've exhausted all other efforts.

Has anyone ever dropped the pan on the MD3070 before? any write-ups?

 

[snowtrac nome]

i've done the commercial versions its messy but straight forward. once the pan is off inspect the harness inside the trans, I have seen wires break at the cannon plug going through the case we also had harness failures in Iraq, in combat we just changed them heavy monsters. good luck

 

[isaacnasar]

Ok - here's my new questions and maybe IO'm being lazy. The most likely cause per Allison is a white film buildup within the control module. The remedy per the allison manual is to pull the control module and clean it with mineral spirits. Why can't I drain the transmission fluid, put a gallon or two of mineral spirits to flush it then refill with transmission fluid. Seems like a lot of work to just flush it.

 

[Suprman]

You cant get all the fluid out and to mix mineral spirits into the whole system is probably not the best idea.

 

[coachgeo]

What Will says and also odds are other components in the tranny are not compatible with mineral spirits so while it might help with that module that way it may harm other items and open a whole new door of problems. ... Another words, one can rinse their tootbrush with gasoline just fine..... but their teeth and gums are not going to fair to well as a result.

 

[Another Ahab]

What Will says and also odds are other components in the tranny are not compatible with mineral spirits so while it might help with that module that way it may harm other items and open a whole new door of problems. ... Another words, one can rinse their tootbrush with gasoline just fine..... but their teeth and gums are not going to fair to well as a result.

Got it. Because like, if you're a smoker, there might be trouble later:

 

[coachgeo]

Got it. Because like, if you're a smoker, there might be trouble later:....

yeah something like that

 

[isaacnasar]

ok - thanks for the advise - I'll get it in the garage and start wrenching - will report back my findings.

 

[isaacnasar]

Here's the update for any that are interested.

I brought the truck to an Allison Mechanic that works on school buses for the local school district.

He pulled the Control Module and replaced the sensor. While everything was apart a new harness was also added for good measure.

The only complicated part was getting the control module out after the front driveshaft was removed. There was very little clearance to bring it down straight without contacting the transfer case. A little bit of patience and 3 transmission jacks and it was out.

With everything back together, the truck drives great.

Now on to my next project of high speed gears or larger tires, or both. 55MPH and the engine is screaming, I usually end up cruising around 50MPH

 

[coachgeo]

Here's the update for any that are interested. ..... With everything back together, the truck drives great.

Now on to my next project of high speed gears or larger tires, or both. 55MPH and the engine is screaming, I usually end up cruising around 50MPH

Thanks for the update. Congrats on having a driving rig now. Glad you had that tranny mechanic resource available to you. As to screaming engines; are you use to diesels? They like to be worked. Screaming (when compared to a gasser) is when they are most happy. But your right in that if you want that proper screaming at 60+ you'll have to make changes to gear ratios.

 

[isaacnasar]

It is such a relief to have nice smooth shifts. It did take about 20 minutes of driving for the transmission to re-learn how to shift smoothly. It was shifting pretty crappy for a little while but got smoother after a short drive.

I'm used to my Humvees which sound like they will implode when driven at 55MPH +.

 

[Another Ahab]

The only complicated part was getting the control module out after the front driveshaft was removed. There was very little clearance to bring it down straight without contacting the transfer case. A little bit of patience and 3 transmission jacks and it was out.

Glad you got your problem solved.

Was that all at the same time with the three jacks?! Or are you meaning that the third one used was the charm?

 

[isaacnasar]

one jack to lower the control module two jacks to push the back end of the transmission (via the transfer case) up about an inch.

The tail end had to come up a little so that the control module could come down perfectly straight. They supported the transfer case with the two jacks and lowered the truck down an inch on the lift.

 

[Another Ahab]

one jack to lower the control module two jacks to push the back end of the transmission (via the transfer case) up about an inch.

The tail end had to come up a little so that the control module could come down perfectly straight. They supported the transfer case with the two jacks and lowered the truck down an inch on the lift.

 

[SrqRyan]

Here's the update for any that are interested.

I brought the truck to an Allison Mechanic that works on school buses for the local school district.

He pulled the Control Module and replaced the sensor. While everything was apart a new harness was also added for good measure.

The only complicated part was getting the control module out after the front driveshaft was removed. There was very little clearance to bring it down straight without contacting the transfer case. A little bit of patience and 3 transmission jacks and it was out.

With everything back together, the truck drives great.

Now on to my next project of high speed gears or larger tires, or both. 55MPH and the engine is screaming, I usually end up cruising around 50MPH

Hey thanks for posting your issues, I'm experiencing similar issues with my lmtv. I got the truck missing the alternator. test drove it and would drive okay until it started having issues of staying in one gear until I restarted the truck or cleared it. Ive installed an alternator now and it continues to do it. Im wondering if you can help me understand what you meant by control module and senor. I hope my issues aren't that but I do need to change my fluids anyway so if I can inspect it or just change it when Im in there. Im starting today to trace the wiring and change the output sensor

I tried to direct message you but Im not allowed to yet

 

[TomTime]

Hey thanks for posting your issues, I'm experiencing similar issues with my lmtv. I got the truck missing the alternator. test drove it and would drive okay until it started having issues of staying in one gear until I restarted the truck or cleared it. Ive installed an alternator now and it continues to do it. Im wondering if you can help me understand what you meant by control module and senor. I hope my issues aren't that but I do need to change my fluids anyway so if I can inspect it or just change it when Im in there. Im starting today to trace the wiring and change the output sensor

I tried to direct message you but Im not allowed to yet

This an old thread and the person you responded to looks like he hasn’t been on here since May of 2018, so he most likely is not on here any more. You can check on a members last time on site. By just making a quick touch on a touch screen or hover over the members site name, it will show you when the member joined and the last time they were seen on the site.
Good luck.
Tom.

 

[coachgeo]

check your batteries...... as in you must have solid good 24v into bats AND back out or your transmission will do odd things. Also it may need to re-learn shifting. oh... and thanks for searching first...... That is the right thing to do though TomTime has a point on quoting someone in an old thread. Have gotten into habit of clicking over to users profile in such a scenario to check their last post date.. (this is what TomTime did)