2002 2500HD Allison Problems - Chevy and GMC Duramax Diesel Forum
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Old 05-24-2011, 01:59 PM   eBay Motors  #1 (permalink)
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2002 2500HD Allison Problems

I had this posted in the 911 section but wasn't getting much attention. The problem is a little less urgent now, as I have given up on getting this truck back on the road anytime soon. 2002 2500HD 8.1 4x4 gas with Allison transmission.

On a recent road trip, no load, i started having some tranny issues, once the tranny got good and warm. I would stick in first, or sometimes second. When it sticks in second, it acts retarded. When it sticks in first, everything is all good. With a little patience I can get moving again. I limped it home, drained fluid, and filled back up. Drove it 30 miles, drained fluid again, replaced spin on filter, and filter in the pan. My magnet is still in place on the spin on. Topped fluid back off, but the problem persists once the tranny gets warmed back up. Shifts and drives great until warm, then the next time you stop, it may shift 1-2, and kick back and stick in first, or shift 1-2-3, kick back into 2nd and all you have is 2nd until you shut the truck off. No first or reverse. Reverse blinks when its stuck in second. If it gets stuck in first, R will still work. I'm in a pinch and need to get this truck back on the road pronto. It might as well be undrivable until it is fixed. All my gear indicators light up so I'm not sure if my problem is the NSBU switch or not. SES codes are P0746 and P0776. I have done as much research as I could, posted on a gas burner forum with no luck. I have read a bunch of threads on here and performed a search, but didn't read anything that sounded like my problem. Is checking for a stuck solenoid easy? If it was stuck, wouldn't it be stuck all the time? It drives perfect until warm.
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Old 05-24-2011, 02:53 PM   eBay Motors  #2 (permalink)
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These two codes indicate that your clutches are not applying and releasing on time. Usualy this means a speed sensor problemat the turbine speed sensor ) on top of the case or the output speed sensor on the transfer case ( 4X4 ) or extension housing (2X4 ). Could also be a loose tone wheel in the transfer case. Could be wiring at either of the speed sensors.
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Old 05-24-2011, 03:04 PM   eBay Motors  #3 (permalink)
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Alright, how do i check that? I did notice the speedo gettin kinda jumpy here lately. The rear driveshaft has some play in it for sure. I believe there may be a bearing going out in the t case as well. Seems to be making a bunch of racket these days. I will start there and see what I can figure out. Thanks!
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Old 07-11-2011, 07:21 AM   eBay Motors  #4 (permalink)
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I wanted to update this thread in case anyone finds it in a search later or something. I found out what pump rub was, my t case was dry, and the internals to the speed sensor or tone wheel or something was messed up. Bought a new transfer case from jasper, bolted it in and problems solved.
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