2003 Chevy 2500hd stuck in 3rd gear

Tm090807

Original poster
Member
Nov 8, 2020
2
Texas
I have a 2003 Chevy 2500hd 6.6l diesel. All gears and shifting were working fine. Pulled out on highway today and had to get on it. When going through gears I heard it slip up and rev as if it slipped out of gear. I slowed down and got off road. It seemed to be stuck in 3rd gear. I tried putting it into reverse and it would not work. The shifter doesn’t even feel like it’s moving into gear when I move into reverse. When I move shifter to Drive, it sounds very rough and it starts off in 3rd gear. The truck will not shift out of this stuck gear, not even go into reverse. Had to put home slowly in that gear range. Need some help, What’s going on?
 

Reprise

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Jul 22, 2015
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You've got the Allison 1000, right? I don't know of anyone on this site who has one. Our knowledge would be limited to what we could dig up on Google, I'm afraid.

If I were to guess, 3rd gear is the default 'limp home' mode, same as in the 4L60E that's in most of our trucks (which is a toy, compared to yours). You're probably going to have to take it in to a shop that works on Allisons.

You could try a pan drop / filter / fluid change (not sure if there's an in-pan filter, or just the external (red) spin-on, but that would be the longest of long shots. Could buy you a little time, or make it totally inoperable.
Fingers crossed that it's something very minor, and you're back on the road, soon.

PS: A (very) quick search seems to confirm the 3rd gear limp home mode on this unit.
 
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