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Thread: May be a dumb question. Allison 5 speed controller

  1. #1

    Default May be a dumb question. Allison 5 speed controller

    I know Allisons have there own controllers, A40, A50 etc. My question is can a T42 control these with some wiring modifications or is it just dumb to think this? I have an 2007 Express Duramax that the 4L85E is about to give out again. It was not a cheap trans or convertor by any means and is just not going to work for what I want. I appreciate any input

  2. #2
    Joe (Moderator) joecar's Avatar
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    How many forward gears do the A40/A50 have...?

    The 4L60E/65E/70E/4L80E/85E have 4 forward gears, I have used the 0411 PCM to control other transmissions with 4 gears, for example, many years ago I helped someone get a Nissan 4-speed trans working with the 0411 (he put this trans behind an LS1 engine).

    Do you have any internal wiring schematics that we can look at...?

    Do you have any tech guide pdf's we can look at...?

  3. #3
    Joe (Moderator) joecar's Avatar
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    The T42 will also require some other external signals, and I'm not sure if it gets some data from the ECM over the CAN bus.

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    Lifetime Member THEFERMANATOR's Avatar
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    Won't work. The T42 was never used on a 5 or 6 speed clutch to clutch trans that I'm aware of. The ALLISON shifts rather unique compared to other trans of it's day. You can do some repinning of the ECM plugs, change the ECM OS, and then wire in an A40 ALLISON TCM to control a 6 speed as this has been done by others before. But as to making a T42 work, theres no way I can think of to make it work. And forget the 5 speed as the ALLISON 5 speed TCM cannot talk to a BOSCH ECM. They talk in 2 completely different CAN languages.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

  5. #5
    Joe (Moderator) joecar's Avatar
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    Ok, it's got 5 gears, and it's clutch-to-clutch meaning the TCM has to time the transition of each clutch, both of which eliminate the T42 as a controller.

  6. #6

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    Okay, thank you. So either I make a 6 speed Allison or a really expensive 4L85E.

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