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02 GMC C-6500 With Allison Auto Probs

RTSmith

Senior Member
Joined
Oct 23, 2008
Messages
421
Location
Middle Tenn.
Occupation
Amateur demolition & dirt pusher
Good Morning! I am stuck, literally. I have a '02 GMC C-6500 with the 8.1L gas and Allison AT-545. It was a Penske moving truck that had the frame shortened and a small dump body installed. Generally works great for the little hauling I do. Hauled rock yesterday, all's good except the tarp wouldn't work. Raised the bed, find a reversing solenoid on the frame that runs to the tarp is stuck. Replaced it. Tarp works.

But now the truck won't move. The parking brake (electric) is disengaging, and I can roll the truck with the engine off. But starting the engine, causes the transmission to "lock". It changes engine sounds when shifted into D or R, but it doesn't have the rear end clank it used to have. We un-did the tarp relay (just in case), but no avail.

We disconnected battery for a few moments, no difference. It almost seems like it is in 2 gears at once. ? Maybe? All fuses seem good. One other "detective" item is that when the key is cycled off, the electric parking brakes engage. I don't recall that happening before.

Last caveat- I didn't do the solenoid work. One of the techs at my place did. But he swears nothing else happened or was weird.

Any help, greatly appreciated.
 
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