Allison HT740 Question

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by OllysCustoms, May 19, 2024.

  1. OllysCustoms

    OllysCustoms Bobtail Member

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    May 19, 2024
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    Hi,
    I just recently bought an Allison HT740 to mount to the back of my Big Cam Cummins NT855 350 however, the flexplate that I had will not mount to the current flywheel/torque converter that is on the transmission. From what it looks like it seems that the ring gear is made onto the flywheel and from what I was told before I bought the transmission with the flexplate I possess which also has the ring gear on it that it would bolt right up to the torques converter kind of like your standard GM flexplate to torque converter. Now I researched the transmission before I got it and I know you can mount it to a Big Cam Cummins but everybody that has done it doesn't want to share how they actually mounted it and I contacted Allison but since longer support the transmission they have no information for me. So basically sorry about the long rambling my question is does anybody have any information on how to mate the transmission up to the engine? Any information would be greatly appreciated. Thank you.
     
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  3. BoxCarKidd

    BoxCarKidd Road Train Member

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    Look to the army surplus world. I believe a small cam flex plate will work with that.
    I have one in the junk and will look but I do not thank I have the flex plate.
     
    OllysCustoms Thanks this.
  4. OllysCustoms

    OllysCustoms Bobtail Member

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    May 19, 2024
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    Thanks for your response.... I think the one I possess right now is for the military small cam but it has the teeth on it but the one on the transmission doesn't have any teeth on it it bolts inside the flywheel. I can post a couple of pictures in case you do find the flexplate and maybe once you see an image of it you might have an idea. Just kind of want to get my truck running.
     
  5. BoxCarKidd

    BoxCarKidd Road Train Member

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    Old one was put back in the military storage container the replacement came in. Some pictures might be good. It has been a long time.
     
  6. OllysCustoms

    OllysCustoms Bobtail Member

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    May 19, 2024
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    Here's the pictures of the one on the transmission:
    DSC06015.JPG DSC06016.JPG DSC06017.JPG
     

    Attached Files:

  7. OllysCustoms

    OllysCustoms Bobtail Member

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    May 19, 2024
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    Then here's the flexplate that I have: DSC06018.JPG DSC06019.JPG
     
  8. OllysCustoms

    OllysCustoms Bobtail Member

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    May 19, 2024
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    The transmission seems to have some sort of flexplate that bolts inside what I assume is the flywheel. When I took the bolts out, there are four plates and the eight bolt holes in the center don't line up with the six bolt holes of the Cummins. I noticed at Vanderhagg they had a flexplate for an HT740 that went to a Big Cam Cummins but is no longer available and there was no part number. I checked the rest of today and can't find anything on the web.
     
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