5 ton dump truck transmission locks up when shifted into reverse

[Coot1879]

a buddy of mine recently purchased a 5 ton dump truck along with two transports (which we are installing dump beds on) and a wrecker. Dump truck runs operates fine but when reverse gear is selected, transmission locks up and bogs engine. I disconnected transfer case output shaft and ran the engine up to max RPM and transmission seems to be shifting through all of the forward gears, but once reverse is selected, trans output shaft immedetaly locks up and bogs engine like it is stuck in both forward and reverse gear. Transmission does go into neutral. I checked the switch on transfer case lever and the oil line solenoid on side of transmission, when button is pressed, I can hear/feel solenoid shifting. Oil level is ok and oil doesn't smell burnt or anything. We have another transmission on its way, but I would like to make sure it isn't something simple before we go through the trouble of swapping it out. If anyone has any ideas, please let me know.

 

[R Racing]

What model truck ? M818 ? M929? M930? M917? They all have different Transmittions and transfer cases . So it would be a great help to know.

 

[Coot1879]

29 or 30 which ever one doesn't have the winch. It also has the 250 cummins with the allison 5 speed auto.

 

[gimpyrobb]

Shift cable adjusted correctly?

 

[porkysplace]

TM's for the 939 series trucks
Free to download

 

[Coot1879]

Checked the cable and it seems to be properly adjusted

 

[Coot1879]

I read the manuals and dont see anything that would explain why the transmission would stick between forward and reverse or troubleshooting for a transmission that operates fine in forward but locks and bogs engine in reverse, anyone have any ideas? I may be mistaken but I think it uses the same clutches in reverse as in forward just in a different sequence, so if forward works and doesn't slip, it shouldn't be a burnt transmission. I would think it would be a valve sticking or something else from the truck inhibiting it to reverse.

 

[Monkeyboyarmy]

This is a long shot but check to see if the button on the transfer case shifter is not stuck in. Seems to me that someone said that this button locks up a clutch.

 

[Floridianson]

This is a long shot but check to see if the button on the transfer case shifter is not stuck in. Seems to me that someone said that this button locks up a clutch.

Yea as said the button locks up the torque converter and unlocks the transfercase. It should be stalling in forward as it does it on mine with the 250 but I had the same thought.

Does the wires that goes to the button carrie power or is it a ground and the button compleats the ground to compleat the circut. If it was a ground line and it was cut and makeing contack with the frame/ground then it would stay locked up. Could try WD40 in the button and work it in and make shure as said before the button is comming out of the handel. Worse case disconnect the out going side of the circut.

 

[Coot1879]

Yeah I was hoping it was the problem, but button operates as it should and you can feel solenoid clicking and hear air bleeding from transfercase. Engine/transmission operates fine in forward. I was thinking the valve body is sticking or a stuck forward clutch.

 

[R Racing]

Did you run in reverse in low? You may have damaged your transfer case?

 

[fsearls92]

I had a friend who had a M931A2 that did that same thing when we went to pick it up. I know how he solved it isn't the right way but it worked for him. He would go forward and slam it into reverse. It kept dying then something finally happened and away he went. He still has the truck and that was about three years ago. Not sure how it didn't break something in the transmission, and I would not suggest trying it.

 

[porkysplace]

I had a friend who had a M931A2 that did that same thing when we went to pick it up. I know how he solved it isn't the right way but it worked for him. He would go forward and slam it into reverse. It kept dying then something finally happened and away he went. He still has the truck and that was about three years ago. Not sure how it didn't break something in the transmission, and I would not suggest trying it.

Sounds like a good way to break the transfer case housing.

 

[fsearls92]

Sounds like a good way to break the transfer case housing.

It didn't and the truck is still running great. Like I said though, I wouldn't recommend trying it.

 

[Baradium]

You said it's fine in forward, have you used all forward gears or just driven around at slow speeds?

 

[jcappeljr]

I have a transfer case if needed.

 

[Floridianson]

There is another thread with the same problem. My button sticks or seems to stick sometime and the transmission lockup does not disengage. I cleaned my switch with WD40 but contack cleaner is the best. I have to click my button a couple of times once and awhile in and out to get the trans. lockup to release. I can fell the trans. lockup and release. I checked one of the wires and do believe they are a ground circuit. double check for rubbing on the cab or cut and hitting chasie.
I don't have any trouble with the transfer case interlock releasing and expelling the air just the transmission lockup not kicking out.