LMTV Transmission won't engage

[dadafan]

Hi,

I'm seeing if I can get some quick responses while I go through the manuals.

My push button Allison Transmission will not engage. I push "D" drive, it beeps twice and starts flashing 7 N and won't engage. I'm thinking it is probably a sensor, but I just don't know. Fluid is clean and full. I pushed all the buttons, D, R, N, mode...etc. nothing happens.

Any ideas?

Thanks in advance.

 

[Suprman]

Press arrow up and arrow down at once and you can see stored error codes. There is a code guide online to reference. The harness and connectors going into the trans computer located behind the keypad can come loose and cause all kinds of issues.

 

[dadafan]

Code is 23 12 Apparently something with the shift selector???

 

[Suprman]

Check the harness between shift pad and ecu. Clear the codes. Make sure you have good running voltage. LMTVs have lots of issues with low voltage. If that dosnt work then I would replace the shift pad.

 

[Wile E. Coyote]

One of the keys might be stuck 'on'. I had one of those on a bus transmission do that. Try press all the keys pretty vigourously, cycle power, and see if it clears.

 

[dadafan]

Thanks, I'll try that. Any idea what size nut holds the steering wheel on? It's bigger than 1 1/8, the biggest socket I have.

 

[Suprman]

Tilt the wheel down and you can get the dash panel out without taking it off

 

[dadafan]

OK, I took the ECU out and separated the touch pad from the ECU and disconnected the ribbon cable. I sprayed contact cleaner on the terminals from touch pad to ECU and the pins to the wire harness. Reinstalled everything, fired the truck up until air pressure was right and hit the drive button. The truck went into gear right away. Shut everything down and a little while later started it up again and nothing. Hit the up and down arrow button and no diagnostic code.

I played with the buttons and the engine rpms for a little and got the truck to get into gear. Drove it for about 15 minutes and everything was fine as long as I kept it in drive or reverse. Park the truck, put it in neutral, and then tried drive again....nothing.

Thinking the pad is bad, engine rpms too high, or low voltage. Stopping the truck can be a struggle as it wants to lurch forward as it downshifts from 3rd to 2nd, and I have to stand on the brakes. That's why I'm thinking it may be an engine rpm issue.

 

[Suprman]

Is your speedo jumpy or appear incorrect?

 

[dadafan]

No, speedo is dead on.

 

[Suprman]

You should check all the grounds but if you have good voltage and the speedo is working properly I would say it's a keypad or ECU issue.

 

[dadafan]

OK, I spoke to a WTEC II expert at Transmission Instruments and he thinks my engine is idling too high which is telling the ECU not too allow the transmission to get into gear.. I've tried to find the procedure to adjust engine idle in the tech manuals without luck as of yet. Can someone point me to the right section or provide advice on adjusting the engine idle?

 

[Suprman]

I have one the spring throttle return was weak and it would idle way too high. The trans would always engage though it didnt seem to care about the rpms. I added a big spring on the engine and it fixed it.

 

[tennmogger]

My LMTV behaved like Suprman said, would not return to low idle without assist (toe under skinny pedal). The absolute 'stop' for low idle is a bolt adjustment on the top front left of the engine area. I idled my engine down so transmission shift into 2nd was not so abrupt. Also the truck would sit at stop light without trying so hard to GO while brake is held. I am still using my toe instead of a spring because my leg and foot got tired with the heavy spring required. Got to lube the throttle cable next!

While adjusting, I shortened the throttle position sensor linkage a little too, to fool the trans into shifting earlier. Made tiny bit of difference. That sensor is linked to throttle linkage at the same area the idle adjustment is located, left front top of engine, and a cable runs back about 2 feet to the tp sensor.

Bob

 

[dadafan]

Thanks guys. My truck is like a bucking bronco when it down shifts from 3-2 at a stop light, really wants to go. I'll see if I can make the adjustments.

 

[Wile E. Coyote]

Excuse me if it's overly obvious, but make sure your hand throttle on the dash is down to its lowest position. Sounds dumb, but one of the guys at work wondered why he had to ride the brake and...well...yeah.

 

[dadafan]

Yes hand throttle is all the way down, but I did not try to lift up on the gas pedal to see if it affects the engine rpms. Also, hand throttle doesn't start to increase engine rpms until the throttle is half way up.

 

[dadafan]

Bob, winner, winner, chicken dinner! You got it, my gas pedal was "stuck" down, causing the engine to idle high. The ECU was reading the high RPM's like the tech at Transmission Instruments had predicted and wouldn't allow it to go into gear. Foot under pedal, shifts into gear. Now I need to check the adjustments. Thanks all, I thought this was going to be expensive.

 

[jpinst]

Man you lucked out big time. I got an LMTV with transmissions issues that when I tok it on its first "over one mile" run (of course totally serviced the tranny) it stopped shifting altogether unless I shut the engine down., Eventually had to take it to a a truck transmission shop - repairs cost almost as much as the truck...it really is a role of the dice with these trucks...

 

[tburk49760]

Mine was really lurching at a stop when shifting from 3-2. Would jump forward about a foot! Was also straining while at a stop. The throttle pedal lift resolved it. Went to lube and adjust and found where the pedal connects to the floor had been poorly repaired with some green rubber goo. With much effort, removed the goo and welded a panel after removing the small rust hole. Remounted and lubed the vulcanized hinge and viola. A fine example of a 5 minute job turning into a 3 hour task.