LMTV Transmission Selector/ Control - no display

[Wile E. Coyote]

Every now and then I'll start up the 1993 M1078, and there will be no display on the transmission selector, and you cannot select gears. Turning it off and restarting it usually brings it back (after doing it once or twice), but then when driving it sometimes again gives you no display, and goes into neutral.

I have all the manuals but not the time to go into it at the moment, but just wondered if anyone's come across this before and has a quick fix. I know they had trouble with wiring connectors and what-not on the earlier ones which is probably where I'll start. I have another proverbial "known good" M1078, same year, that I can swap parts with - but hopefully it won't come to that.

Last time I saw something similar was on a transit bus using the same Allison selector panel, which managed to get wet at some point. Transmission wouldn't do anything because it read that the '2' key was selected at startup (dirty water traces making the key turn On), so I'm leaning towards the selector if connections/ grounds don't prove to be the problem.

Weird deal because it drove fine the 80 miles from the trucking yard without a hiccup.

 

[Suprman]

Check all the grounds. There are 2 connectors on the back of the wtec computer. Which is right behind the selector. They seem to have a habit of backing out a bit. I was changing my light switch and mine came right off.

 

[bikeman]

Also check to make sure your circuit breaker for the Transmission EDU is good. that reminds me of a problem I had with a truck here. ensure the connections behind the block are solid too.

 

[Suprman]

There are little plastic tabs that hold the wires with basically spade connectors in place in the power panel. It's spaghetti in there.

 

[73m819]

There are little plastic tabs that hold the wires with basically spade connectors in place in the power panel. It's spaghetti in there.

View attachment 573266

Yep, a very easy in field tactical truck fix.

 

[Suprman]

The 3116 is all mechanical and will start with air fuel and power. You can jump the starter solenoid with a screwdriver without tilting the cab. The trans selector is a different story and you wont go anywhere unless its functioning. There is a vim module in the passenger side underdash with 6 relays and 2 fuses. The vim has neutral safety and other lockouts. You can make up cheater fuse/breaker and relay bypasses like this.

 

[Wile E. Coyote]

Cool. I'll go have a look next week. One problem is that this was a gun truck and had the roof open to the elements for a very long time *and* the cover off of the relay/fuse panel, so I expect to have a lot of electrical...fun...with the thing. Fortunately my voltmeter and I are like an old married couple by now, though I have a little bit going on the side with a test light

 

[Wile E. Coyote]

Sooo...pulled the keypad/ computer and...the problem must've been it was low on water

Yeah, water pooled at the lower connector and there was also some sloshing in the ECU itself, so...that could be better. Not having a lid on the roof for x-years in Ft. Campbell obviously didn't do it any favours. I'm just glad I made it back here before the problem showed up. Changed the ECU out with one from another A0 truck and it works.

I'll clean everything I can clean in the dead ECU - plus one connector on the back/bottom has a pin or two that look corroded, so it could be that easy. Unfortunately I'm not sure this ECU can be relied upon 100% in the future even if I fix it (once water gets in etc.), so I'll have to go shopping for a spare.

 

[tennmogger]

What are the possibilities that this style of Allison shifter could be used on an LMTV? I would like that!

 

[Wile E. Coyote]

What are the possibilities that this style of Allison shifter could be used on an LMTV? I would like that!

When you run "WTEC II" that's one of the shifter formats that comes up - seemingly attached to the same type ECU box. Be fun if they were interchangeable.

 

[Wile E. Coyote]

Yeah. A moment of silence for my TEPSS. And maybe some bagpipes playing. It's parted the curtain and joined the choir invisible. RIP.

A bit amazing I was able to drive this *any* distance, as those circuit boards were in the hot tub a very long time, and I guess the problem only came to light when our drought started evaporating the water and leaving all those extra little circuit paths where none are supposed to be.

So, the search for a replacement begins. There are two main numbers on the box, which seem to be one for the specific version of the basic hardware itself ('small label') - and the second for the particular configuration/ program of that hardware as installed in the FMTV WTEC II configuration ('large label'.)

Running the small label number on the web (and Ebay) gets you a number of the WTEC II TEPSS boxes that look identical, but are programmed for different transmissions in the Allison World..uh..world. Yeah. So, I wonder if it's possible to get one of the more common WTEC II TEPSS units out there and have them repgrogrammed with the FMTV A0 specific program?

In the meantime, if anyone has one they want to sell, let me know. I'll put the 'Wanted' in the right section of the Classifieds too. This 1078 is AOG until I can get one, which right now is...less than ideal.

 

[Suprman]

You may be able to clean it up and resolder any bad connections. Its worth a try. I believe the Allison dealer can reprogram the correct part number to work on your truck. Or you can find a mil replacement that came out of the same series truck.

 

[bikeman]

Just throw it in the dishwasher, it'll clean up.

 

[Wile E. Coyote]

You may be able to clean it up and resolder any bad connections. Its worth a try. I believe the Allison dealer can reprogram the correct part number to work on your truck. Or you can find a mil replacement that came out of the same series truck.

Yup. I used to work on water damaged electronics all the time into the SMT world, but once they went to multilayer boards when you don't have a circuit diagram to help you out - success rates dropped considerably

Fortunately for others who may run into this problem with the FMTV earlier TEPSS setups like mine, the boards are covered with a thin rubberized membrane - sort of a more modern version of the MFP shellac they used to put on military radios back in the BC-XXX and PRC-6, 8/9/10/28 days. The membrane covers everything, including the two main boards, and the vertical boards mounted to the main boards. My pics there primarily show what long term immersion did to the *membrane*, as when I got a brush on the boards and found something that dissolves the membrane with a bit of scrubbing (Brakeleen works well), the boards and most of the components looked pretty good underneath.

Unfortunately, you have to get *under* the connectors mounting the vertical boards to the horizontal boards, and under the main connector. Only way to do that is to remove them, and if you've had experience doing that without popping lands...it's still not fun. Did all that, resoldered it all up - then found a bad trace on the vertical board nearest the casing, and a component basically corroded off the board. When I pulled the board, I saw three of the thru-board holes (which also connect to board intermediate layers/ circuit paths) were corroded through. I re-established the circuit paths I could *see* with jumper wires, but, again, you have no idea what's happening wrt circuit paths on any intermediate layer, and loss off the copper conductor/ tube in the thru-board holes means your chances of retaining any electrical connection with intermediate layers is in the order of nil. And without a circuit diagram, you can't work around it to re-establish broken circuits.

So, after about six hours work or so...still back where I started. There's an Allison rebuilder offering a used takeout for $900 as long as I can re-use my existing keypad, but given all the FMTV series released in parts over the years, I was hoping someone knew of a scrapyard or one of our Supply Line friends who might have a line on one priced a bit more reasonably before I pull the trigger on that one.

Chances are great that some custom IC shorted out anyway, and it's not merely a connection issue. Apparently even with the main vehicle power off, the thing was beeping and flashing all weekend long when I wasn't around...so...yeah.

 

[Mario55645mm]

Check all the grounds. There are 2 connectors on the back of the wtec computer. Which is right behind the selector. They seem to have a habit of backing out a bit. I was changing my light switch and mine came right off.
[/QUOT






Hey where exactly?

 

[Suprman]

What year is your truck?