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02 2500 HD Allison Issues...

Discussion in 'Chevy Trucks' started by exmark1, Nov 20, 2011.

  1. exmark1

    exmark1 PlowSite.com Addict
    Messages: 1,321

    I have a 2002 2500 HD Duramax, Allison Transmission running a 8'2" Boss V-Plow

    Last nite one of my guys calls and tells me that in clunks loudly and lunges when going into gear from park or neutral it does the same thing going into forward or reverse.

    The truck has 139,000 miles on it and has never giving us any troubles, I have checked all the u joints etc... and they appear to be fine.

    Any suggestions? The truck shifts and drives fine once it's in gear and going just engages bad
  2. Tom1

    Tom1 Junior Member
    Messages: 9

    Check engine light on? Possibly Torque Converter Clutch solenoid.
  3. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Need to check and reference any DTC codes before doing anything besides checking fluid level.
  4. exmark1

    exmark1 PlowSite.com Addict
    Messages: 1,321

    No lights came on ever it went from working perfect to what it was instantly, I went to pull it into the shop today and it was working perfectly fine again. It's going into the shop in the morning, thinking it had a sensor issue that sent it into safe mode.
  5. chevyzrule810

    chevyzrule810 PlowSite.com Addict
    Messages: 1,288

    check engine light on?
  6. exmark1

    exmark1 PlowSite.com Addict
    Messages: 1,321

    No it never came on
  7. chevyzrule810

    chevyzrule810 PlowSite.com Addict
    Messages: 1,288

    let us know what you find out
  8. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The fact that the CEL isn't on doesn't mean there are no codes stored so I'm sure they'll find some when they scan it.
  9. chevyzrule810

    chevyzrule810 PlowSite.com Addict
    Messages: 1,288

    I've put a park neutral position switch in a 2001 2500HD because it wasn't shifting right and the check engine light was on.Not hard to replace at all right on the side of the transmission.
  10. 496 BB

    496 BB Senior Member
    Messages: 789

    Ive had a few issues with no CEL. Have it ran like B&B said. Youd be surprised what doesnt blink that light.
  11. Schnabel Plowin

    Schnabel Plowin Senior Member
    Messages: 139

    Limp home mode for an Allison locks out all gears except 3rd and reverse.
  12. exmark1

    exmark1 PlowSite.com Addict
    Messages: 1,321

    That's what happened to him when he drove it back to the shop when it started, I didn't get a chance to stop into the shop today and see what they came up with
  13. samjr

    samjr Senior Member
    Messages: 481

    I got the samething going on

    I took my truck to trans shop they said T-case i said nope but they rebild anyways.So they call and say we do not think we fixed it i LOL @ them.I told them its in the Differential in the back. 4X2 can feel it abit but when in 4X4 by pluck man can u feel and hear it:help: O an i got the 6.0 and 4L80E. Thats y i think we got the same problem just dif setups
    Last edited: Nov 22, 2011
  14. Philbilly2

    Philbilly2 PlowSite Veteran
    Messages: 3,770

    I am going to let it all ride on an NSB switch. It will be a black or tan colored box attached to the drivers side of the transmission. There will be two wiring harnesses and the shift linkage attached to it. They are under $100 and you can change it in you driveway with a 13MM socket and a 15MM box end wrench. I have had those boxes go out on more of the 5 speed Allisons then you will believe. When they go bad, the truck and the transmission are no longer on the same page.
  15. blowerman

    blowerman PlowSite.com Addict
    Messages: 1,275

    I'm betting on this one also. They can fix a million other parts and in the end it will be the NSB. If you feel like taking it in, shouldn't even be a $200 repair. Otherwise as stated, parts less than $100.
  16. JD Dave

    JD Dave PlowSite Fanatic
    Messages: 11,194

    An Nsbu switch does cause some funny symptoms. If the truck is stock I'd put my money on that also. B and B is right though you should get the codes read and go from there. Parts replacing gets pretty expensive.
  17. exmark1

    exmark1 PlowSite.com Addict
    Messages: 1,321

    Truck is totally stock to my knowledge, I have done nothing to it! The transmission had a low voltage code in it, the transmission guy is trying to tell me that the truck needs new batteries and that would correct the problem... The problem is we just had the truck looked over for winter and both batteries passed a load test at over 900 CCA with no issues and both are only a year old.

    Any ideas if that code could work with what you guys are thinking? The truck is driving great now and I havent done anything to it yet
  18. got-h2o

    got-h2o 2000 Club Member
    Messages: 2,440

    Another vote for the NSBU. See if you have a local Detroit Allison dealer. IIRC my last one from there was like $45.
  19. White Duramax

    White Duramax Junior Member
    Messages: 13

    Like the others said, get an NSBU. They are known to act up when they get wet in snow/slush conditions.
  20. Philbilly2

    Philbilly2 PlowSite Veteran
    Messages: 3,770

    If NSBU goes bad, no codes are thrown. First time that it happened to me, it took me a couple of hours to figure out what went wrong, now I carry a spare on the service truck.