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Discussion Starter · #1 ·
I have a 2002 2500HD with a 8.1 and an Allison transmission. The first problem I noticed was that when I shifted it into gear, (forward or reverse) the dash indicator only flashed behind the letter, (D or R). Now when I shift it into 'R', there is no movement and only 3rd or 4th gear when shifting it into 'D'. Any suggestions?
 

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How's the fluid look?

The Allison has a separate computer on it, so you'll need some fancy scan tool too read it. Typically, a problem with the Allison won't even generate a CEL. Check for codes... my hunch is that it's electrical (unless the fluid is nasty).
 

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These transmissions are fairly bullet proof behind the 8.1 and 99 percent of the time the problem you describe is caused by a bad neutral start switch which is located on the outside of the trans where the shift cable attaches.
 

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Discussion Starter · #4 ·
Thanks for the suggestion guys. I had the transmission serviced about a year ago and the fluid is still nice and red. I will check the NSS and see if that is the problem.
 
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