Solenode on side of the Allison, what is it for ?

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I've read on here that the button on the transfer case shifter can cause this behavior. I'm trying to sort it out in my head as to what it does. Common logic would say that it disengages the torque convertor to allow easier shifting from high to low on the transfer case but I think it does the opposite and locks the convertor in. I may have it wrong and somebody smarter than me will chime in but I know I've read that the button can be a culprit for your exact issue.

The button on the transfer case lever actuates the air solenoid and drops the air pressure so the transfer case will shift.

TRANSMISSION 5TH-GEAR LOCKUP SOLENOID VALVE - Activated by transmission control switch and transfer case switch, the 5th-gear lockup solenoid valve directs main oil pressure of transmission to the transmission governor system. This puts transmission in 5th-gear, creating less drag on transfer case synchronizer which permits smoother shifting from one transfer case drive range to another. Refer to TRANSFER CASE CONTROL SYSTEM OPERATION, for further details


If that valve is malfunctioning it would put the truck in 5th gear so making it move would be hard from a dead stop .

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86m1028 said:

Wes
Allison dealer is telling me that solenoid is not needed.
Its a military only apt.
Remove & cap the ends ?
Transfer case button seems to be operating correctly,
its raining here today gonna try & test button tomorrow.

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You will not be able to shift on the fly. The part is on Ebay for cheap using # 11669826

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Remove the parking brake.

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Reading through your signature, is this the M923A2 that you converted into a M925A2? Back when the Army still used M936 Wreckers we'd play tricks on new guys and engage the power take off when parking the truck. We'd know if they checked the truck over pretty quickly if we heard a bang and the Wrecker shut off immediately. It never hurt anything but pride. Is your PTO engaged by chance?

I think you have a fuel problem instead of a transmission problem.

He said it will drive in low range around the block. And some other stuff. I figured not enough pressure to keep it running under load as well

sandcobra164 said:

Reading through your signature, is this the M923A2 that you converted into a M925A2? Back when the Army still used M936 Wreckers we'd play tricks on new guys and engage the power take off when parking the truck. We'd know if they checked the truck over pretty quickly if we heard a bang and the Wrecker shut off immediately. It never hurt anything but pride. Is your PTO engaged by chance?

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Thanks, but no it is just a straight m923, no pto.

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It doesnt have enough flow to keep the motor running under a load. No different than lugging a manual transmission. Engine doesnt have enough pressure supply for fuel to overcome to load.

A 931a2 the other day would run its butt off with nothing behind it. Put a 16000lb trailer behind it and it wouldnt get over 25mph cause it was starving for fuel with the load on the motor.

In low range the motor doesnt have to work near as hard to move everything since it's a double reduction of work basically. If the converter had issues it may act the same in low range vs high range.

86m1028 said:

Please explain how a fuel problem would cause converter lockup issues.

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How does a little button on the end of the T-case shifter affect the transmission? It's all about how things interact with each other. The automatic transmission is a slave to the engine. It does what the engine tells it to do, whether the action created is intentional or not. There are several engine problems that can typically manifest as a transmission problem, when there is actually nothing wrong with the transmission at all.

So you're sure the converter is constantly locked? I haven't seen where you posted that the converter was definately locked and how you came to that conclusion. It "feels" like it's locked is not a diagnosis. You did ask for ideas. I gave you mine and Wes has posted the reasoning behind it.

Cracked fuel lines that are sucking air and clogged filters can create this exact same symptom. You did say the truck sat for a while so....

Piggybacking off of what Swamp posted, install the driveshafts to the transfer case. Start truck, build air pressure, release parking brake and shift into gear ready to give some throttle if necessary. The torque convertor shouldn't be locked at all in first gear, it shouldn't lock in until the trans shifts into 2nd gear once ground speed referenced by the internal governor send oil pressure to the convertor to "lock up". Once locked up in second it stays locked up until speed drops and the governor inside the transmission releases the oil pressure to the convertor. Try to get it moving and post back the results. My truck is NHC-250 powered and the idle speed drops about 50 rpm from 650 to 600 when shifted into gear. It shakes the truck as the transmission engages rather rough compared to my Silverado but it's done it that way since I got it so I don't worry about it.

Does it die if you shift to reverse? Try putting it in gear run the RPM up a little, then slowly pull the brake up and see if it starts to lug the engine hard. Or just take some more parts off...

My vote is the button on the transfer case shifter and a locked up converter. I've had several 5 tons that have had that same issue with a sticky button.