Do I have a 4 or 5 speed Allison?

Discussion in 'GM Powertrain' started by timmerado, Feb 6, 2011.

  1. timmerado

    timmerado New Member

    After days of searching, I have decided the best thing to try is replacing the nsbu switch, but now I don't know for sure if I need a 4 or 5 speed switch. It would seem simple enough, I have p r n d 1 2 3, four speeds right? But it seems like most allisons are 5 or 6 in these trucks, so maybe I need to count OD as another speed? It is a 2002 with the 8.1. How can I tell for sure? Thanks
  2. racekid91

    racekid91 Rockstar 3 Years 100 Posts

    Pretty sure Allison Transmissions were either 5 speeds, or 6 speeds. I think your's should be a 5 speed, I think the 6 speeds came out in like 2006 or 2007 for the Duramax's
    Last edited: Feb 6, 2011
  3. timmerado

    timmerado New Member

    Thanks, I think you're right. I guess the 4 spds are non-allison 2500 HDs. I ordered the 5 spd nsbu so hope it works. All the on-line research points to this. Thanks again
  4. racekid91

    racekid91 Rockstar 3 Years 100 Posts

    Correct. If you had a 4 speed, it would be the 4L80E

    DAREDEVIL Rockstar 4 Years 1000 Posts

    YEP, all the above
  6. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner 1000 Posts

    maybe a dumb question. did the 8.1 come with the allison. I thought the allison was for the Duramax diesels and not the gasser. so If its the 8.1 it wouldnt it have the 4l80E correct? the 4l80E is a 4 speed
  7. Taddpole

    Taddpole Member

    I just looked at the sales literature that I got when I bought my 2003 2500hd D/A new in Aug of 2002. It shows the 5 spd allison as an option for the 8.1. The only problem I've had is the connector on the side of the TCU was not plugged in completly during assembly. This caused the trans to go into 3rd gear limp. Other than that the trans has been perfect.

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