NP241 behind an Allison

Discussion in 'Transfer Cases' started by 99BurbK15, Sep 15, 2020.

  1. 99BurbK15

    99BurbK15 Newbie

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    Hello everyone,

    I’m in the process of swapping a LB7/Allison combo into my 1995 Chevy k2500 that originally had the 6.5/4l80e. I was wondering if I could make the old NP241 transfer case work properly? Everything works except the input shaft is a 32 spline and a Allison has a 29 spline output shaft. I removed the input shaft that was in it and I bolted to the back of the Allison and even the shift linkage fits right in its factory location. I know that transfer case was also used behind Cummins drivetrains and from what I can find are also 29 spline. Also I’ve heard of some people swapping a input shaft from a 261xhd. Just was wondering if anyone has done something like this. I know it would make more sense to find a complete 261xhd but I thought I’d at least consider using the 241.

    Thanks to everyone in advance.
     
  2. andy396

    andy396 GMT400 Enthusiast

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    I wish I could help you out with your spline dilemma, but you’re right that mating it to a newer TC is probably the way to go. What I did want to say is we REALLY need a build thread for this venture!
     
  3. b454rat

    b454rat I'm Awesome

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    Yes you can use it. You need the input with the correct 29 spline, I believe a 1/4” spacer behind the gear bolting it in. I was gonna do this exact thing but opted to sell it all lol. I’ll see if I can find the post on CK5.
     
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  4. 99BurbK15

    99BurbK15 Newbie

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    Andy, Yea I guess I should probably start a build thread or find the old one when it was still a 6.5.

    b454rat, that would be great if you could find that post as I would like to make it work
     
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  5. b454rat

    b454rat I'm Awesome

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    1. It is possible to put an NP241 behind the Allison. I have a ZF-650 in my Tahoe behind my Duramax. It runs the same 29 spline output as the Allison does and I have an NP241 in mine. The input gear for an NP261XHD or NP263XHD found behind a Duramax is nearly identical to the input gear on an NP241. The only modification you will need to do is either to machine down the bearing shoulder on the input shaft so the input gear sits about 3/16" deeper than it did before or you need to space the input bearing forwards by the same amount bit to allow the gear to sit deeper (I used the NP261 input bearing IIRC). I opted to space my input bearing and I haven't had any problems at all with it. I just made a spacer out of 3/16" plate steel. The NP241 is plenty strong enough to handle the 8.1L. This would save you a pile of re-wiring and you'd wind up with a far inferior transmission with a 4L85E anyways.
     
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  6. 99BurbK15

    99BurbK15 Newbie

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    That’s really good to know and Thank-you for the confirmation that a input shaft out of a NP261XHD or NP263XHD will work, I’ll have to get one ordered. Would you happen to have any pictures of the spacer you made?
     
  7. b454rat

    b454rat I'm Awesome

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    I personally didn't make one, nor did I do anything with that setup. I'll search over on CK5 again, I think there was a pic.
     
  8. b454rat

    b454rat I'm Awesome

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  9. b454rat

    b454rat I'm Awesome

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  10. Supercharged111

    Supercharged111 I'm Awesome

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    Good stuff, and I second/third/fourth the need for a build thread. I hear the dmax swap is a real asspain.
     

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