Allison Transmission problem

[Carol Bordwell]

I have a question? I have a 2005 GMC 1Ton Dually Duramax w/Allison transmission,, have had it for 4 years. I have an ongoing problem that no dealer has been able to identify.
It is intermittent, but while traveling on cruise on a hill it will start to shift to 4th, clunk, then lock into 4th gear, check engine light comes on. Watching the temps closely on transmission, it is not overheated when this happens. I then have to pull over, shut truck off for a few minutes, restart, and I am good to go. The check engine light will stay on for a while, which according to Dealer it will for a period of time until it proves all is well. All works well until the next time it decides to kick out again. I have had all sensors replaced on transmission, all dealers that have worked on it cannot get it to do it of course.
It is now out of warrenty, but I would like to cure this problem w/o having to keep replacing parts, the sensors were $500.00 which I had to pay for. The dealer was willing to change one at a time, but I live out town, and was not willing to keep going back, so tried all three.
Anyone else experience this problem?
The truck just turned 40000 miles.
It has put me in some uncomfortable situations when I am not able to safely pull over, but have to slow to prevent overheating.
The shifting problem has occurred even when I am not pulling anything.
Any advice would be welcome.
Thanks

[Trailer Trash 2]

Have you tried to put this question on the Chevy Duramax forum Im sure that there will be a person that can answer that question real quick. and of course maybe here too.

Why not try hit it at both ends.

http://www.thedieselstop.com/forums/

Opps sorry that was a ford only I'll look for the chevy one found it ,

http://www.dieselplace.com/forum/index.php?

[SlickWillie]

So, did they pull a code after the light came on? IIRC, anytime the light comes on there is a code set.

I would go to the Diesel Place site. Those guys live and breath Duramax and Allison over there. Look for a guy with the screen name Mike L. He rebuilds the Ally trannies and I feel sure he will give you his opinion.

[gpats]

Sounds like a solenoid that isn't always doing it's thing---go to a different dealer and buy the extended warranty and wait awhile--the warranty is cheaper than the overhaul---mine would have cost $3800.00 for the complete overhaul--

[thor]

do you have on star? if you get a code you can call on star while the code is there or the problem is present and the can diagnose the problem.that cluck might be the lock-up converter not unlocking.when you shut down then the converter unlocks.or it could be the solenoid.it is possible to get another bad solenoid right from the dealer.check the fluids are clean and topped up.does the truck upshift after it has down shifted. if not then it is the solenoid.this is not letting it shift up.or it could be the presure switch.

[Carol Bordwell]

Thanks to all of you for input. I did get a message from Mike L as suggested from the diesol place, what a great site. He gave me his input, I now need to make appt at dealership, and have code checked.
He suggested I change the TCM with a known good working one.
When this problem happens it won't shift at all up or down until I shut off ignition, and restart, then all is good.
Thanks again to all of you, will let you know what I find out.
Mike

[Trailer Trash 2]

quote:Originally posted by Carol Bordwell

Thanks to all of you for input. I did get a message from Mike L as suggested from the diesol place, what a great site. He gave me his input, I now need to make appt at dealership, and have code checked.
He suggested I change the TCM with a known good working one.
When this problem happens it won't shift at all up or down until I shut off ignition, and restart, then all is good.
Thanks again to all of you, will let you know what I find out.
Mike

For sure We'll be waiting to see what the outcome will be .
Good luck and happy hollidays.

[Tom S.]

Mike L. is extremely knowledgeable about the Allison transmission, as well as the rest of the drive train.