Allison Clutch tie up

[KenZ]

You may have read my other post about overheating the engine and transmission. I got the heads replaced on the engine and everything is good to go. I was already having intermittent trans problems before anything happend. After getting the truck running it was going fine--even the transmission.--that was before I replaced the heads due to pressure in the radiator. After that, when I went to drive the truck it had returned to its old ways--getting stuck in 5th gear with no reverse, or just 3rd or limp mode with reverse. It was throwing some codes.

After reading some other post, I pulled the round connector to the transmission and it had transmission fluid on it, so I cleaned it and put it back and all the problems seemed to go away. The codes disappeared and it would shift through all gears like it should, although a little hard on the shifts.

Then later it started doing something else. In the morning after sitting overnight, I would notice that as I put it in gear it would start to roll forward and then something would feel like a shift and it felt like it didn't have much power to the wheels. This was mild at first.

Now in the morning it is major. It will start to roll and go and then after a second or two, bam another clutch comes on and it is in a real bind and won't move unless I really hit the pedal. No codes come on. I did force it through once and got a P0777 code.

After the fluid warms up, the problem is less and I can drive it. After shifting out of that low gear, it doesn't seem to have any tie up and the higher gears seem to work fine.

It didn't do any of this until I pulled the round connector and cleaned it.

I took it to the Allison dealer and he was going to look at it and let it sit for 4 days and then when he went to drive it, it was cold and of course a major tie up. He just called and said we have to pull the transmission and I can only quote a replacement at $4500. I don't think they really wanted to even look at it. Small potatoes for them.

So I picked it up and drove it home. I have a line on two used transmissions, one at $950 and 157k miles, the other is from a wreck $1250, but mileage is unknown at the junkyard.

My question is --can the clutch tie up be caused by electrical problem, wiring or solenoid, or possibly a sticking valve or trash somewhere. Is there something I can do to check it out before a complete replace?

I would hate to replace the transmission to find out that it was some electrical issue and still have the same problem

Thanks for any comments or thoughts you may have.

Ken

[DmaxMaverick]

Not sure about the fluid in the connector, but it could be related to your current problem. Otherwise, it has a leak it shouldn't have.

After sitting overnight, the torque converter is draining down, causing your experience. Try this: Start it in the morning and let the engine run for 3-5 minutes and don't shift from P, turn it off, start again and try to repeat the previous condition. My guess is it will be normal. The run time allows the TC to fill and purge the air. Not shifting from P prevents that air from moving through the shift solenoids and clutch apply actuators, which causes the longer lasting condition. The time it takes to warm up the engine and tranny is enough to purge all the air from the system, and not necessarily the temp that clears the problem.

If it is the drain down condition, there is a valve repair for the problem (not even close to the $4500 you were quoted). However, it isn't hurting anything by doing this, only an inconvenience. The fluid in the connector could be fluid overflow draining down to it. Check the top areas of the tranny for fluid, which can vent when the TC drains overnight.

[KenZ]

Thanks, I will try that. I have let it idle, but not for nearly that long. I think the fluid was from when the line blew. Transmission fluid went everywhere. I forgot to mention that there is no problem at all in reverse.

If it is the drainback, why now? I never had the problem before.

I will let you know.

[KenZ]

I tried idling it for 5 min and it didn't help. However, after the transmission warmed up the tie up seems to lessen. Sometimes going away altogether. then I might shut it of or put it in park and when I go to drive the lock up is back. For some reason it seems to do it when the fluid is cold and intermittent when fluid is warm. That is how it appears to be at the moment.

[KenZ]

Problem SOLVED!

I decided to do a little investigating and pulled the pan and took the solenoids out. Of course, the last one I pulled was the culprit. Either the A or B, I don't know which is which. It is the one on the left looking at them from underneath. The P0777 code suggested the B solenoid was sticking or not releasing. The little screen filter was completely plugged! I pried the plug out and it appears to be melted plastic. I knew I got the transmission hot! Now I wonder where the plastic came from!?

Put everything back together and no more clutch tie up! Ran great, shifts a little hard, but I am hoping that will smooth out.

DmaxMaverick, I appreciate your responses to my post.

[JohnC]

shifts a little hard, but I am hoping that will smooth out.


Probably has to re-learn all the shift pressures. Search around for a way to reset it back to default. It'll learn faster then.

[maverick_935]

A scanner should be able to reset the tranny to re-learn the shifting quicker