2002 Chevy Silverado 2500Hd Allison Tranny Issue

[GP84]

We have a 02 Chevy Silverado 2500HD 8.1 we are having issues with the Allison transmission. Going down the road it will make a loud noise and get stuck in 3rd gear. We then pull over and shut the truck off then turn it back on. Once we do that we have all the gears start working correctly. We took it in and the mechanic said it needed to be rebuilt. Well we had it rebuilt and it didn’t correct the issue. We took it back and they replaced the valve body and speed sensor, then they reprogrammed the computer. That still didn’t fix it. 
I don’t know what to do at this point, I can’t find a good repair shop that knows what they are doing and can work on an Allison transmission. Any help please

[Bobby Automotive]

It’s the transfer case. I had exact problem! The shims in the transfer case and if you hit a bump the slop from wore delrin shims causes the transmission to go into limp mode. Purchased GM rebuilt transfer case and problem gone. I was at about 150,000 miles. 

[davester]

Um, what delrin shims in the NP261/3XHD transfer case are you talking about?

 

Edited April 13, 2021 by davester