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Putting a 54 Flattie on a YJ frame

Discussion in 'Flat Fender Tech' started by J Michael, Oct 8, 2010.

  1. Oct 8, 2010
    J Michael

    J Michael Member

    Burney, CA
    Joined:
    Sep 14, 2010
    Messages:
    151
    I recently purchased this project from my next door neighbor. He got it started by bringing home this 54 flattie and then brought home a 92 YJ rolling frame. After a couple of years sitting, he offered it to me and I jumped on it. He intended on cutting the YJ frame to fit the body, but when I got it in my garage and studied it for days, I decided to leave the frame as is and stretch the body. In addition to the YJ frame the jeep came with a 231 Buick odd fire and a TH 400 transmission. I would like to keep all the YJ running gear intact and somehow plug the engine and transmission into a adaptor and transfer case. At the moment I am thinking of buying an adaptor that will match up the TH 400 to a np241 transfer case.
    As for the body stretch, I have found several examples on line for ideas and I like the idea of stretching the body in two locations, through the door way and right behind the door way. I might have to stretch it in a third location which will be somewhere up front. The wheel base of the YJ is 14" longer than the 3B, but the overall frame length calls for about 18" of body stretch. Experts of body modifications tell me the first cardinal rule is to make sure the rear wheel well is centered over the rear wheel, if so this will leave about 2 inches of frame sticking out behind the tub. I'm not sure I like that but that's the way it might end up. I welcome the additional room in the cockpit area and the two locations will help in keeping some of the original porportion of the tub.
    Here are some photos of what I am working with. Any advice will be very much appreciated.

    Here's a picture of the tub sitting on the YJ frame.
    [​IMG]

    This picture shows the motor mocked into position and the tub pushed forward to where it will not interfere with the motor and tranny.
    [​IMG]

    My 231 Buick waiting to go into the flattie.
    [​IMG]

    The TH 400 automatic transmission I'll be using.
    [​IMG]

    I originally thought I would find a np231 to put in the jeep because that's what was in there before and I have the driveshafts to match up, but looking at the costs of an Avanced Adaptor adaptor to match up to my transmission, I think I might be better off buying a used adaptor on ebay that matched my transmission to a np241 transfer case and deal with the drive shaft later.
    I would like to get the adaptor as soon as possible so that I can install the motor and build motor mounts. This will allow me to go ahead with the body stretch knowing how far forward I can go with the tub and firewall.
    It looks like the tub stretch will amount to 14" and then about 3" to 4" on the front hood and fenders.
    I'm also thinking I want to keep a fair amount of room in the engine compartment to allow options for what ever engine I might want to change to in the future.
    I don't intend to go rock climbing with this jeep, I prefer more to back road exploration with my wife and dogs.

    [​IMG]

    There's a little rot through in the driver's rear corner under the gas tank.
    [​IMG]

    [​IMG]

    This will be a slow project that moves along as I have money to spend on it. Being retired and on a fixed income, that will be slow. I have lots to do in the mean time with clean up and painting. I might have to sell a motorcycle or two if I feel the need.

    Mike
     
  2. Oct 8, 2010
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
    Joined:
    Mar 29, 2007
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    It's very hard for me to visualize a 14" longer 3b. Maybe after it is stretched, the look will grow on me. Although I am more into originality/restoration, I don't mind seeing a well done mod. Your idea of what you would like to do sounds very energetic. Will be watching your posted build/progress.
     
  3. Oct 8, 2010
    lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Huntingdon PA
    Joined:
    Sep 20, 2002
    Messages:
    3,437
    Sounds like a very cool project Mike. I think it will look good... and it sounds like you have the eye to make it look proportionate. Keep us posted as you make progress!!
    :tea:
     
  4. Oct 8, 2010
    EricM

    EricM Active Member

    Southern California
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    Dec 19, 2007
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    1,019
  5. Oct 8, 2010
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Aug 10, 2003
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    I'd do it the way that Jeep made the CJ-6. If you can look at a CJ-6, that will make things clearer. The CJ-6 splice goes between the door and the rear wheelwell, keeping the existing proportions of the door and wheelwell. Here's an archive pic of the side of my CJ-6 that may help:

    [​IMG]

    and of the interior

    [​IMG]

    IMO this way makes the most sense, becasue it preserves as many of the features of the tub as possible. You'll need to make a bulkhead to go under the floor to replace the rigidity that the kickup would have made in the center of the floor. You can see the bulkhead in the top picture, in the wheel well and in front of the tire.
     
  6. Oct 8, 2010
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
    Joined:
    Sep 23, 2002
    Messages:
    12,529
    A friend of mine did something similar about 10 years ago. He had a frame built to his specs, then bought a replacement steel body and stretched it. He did it similar to what Timgr is describing. Looks very good and keeps the departure angles good as well. He added a Ramjet motor, 4l60e, aftermarket transfer case, and dual steering Dana 60's and coilover shocks all around. Works very well.

    Regarding the frame in the rear, you could build a bumper that integrates that overhang to cover it up and make it look nice. I have the same issue on my CJ-6 on a Scout Terra frame and that's my intention.
     
  7. Oct 8, 2010
    J Michael

    J Michael Member

    Burney, CA
    Joined:
    Sep 14, 2010
    Messages:
    151
    I like what Jonah did with his stretch. I am leaning towards his idea, but I also will need to do some stretching across the front fenders and hood. I don't want a long tub and a short front end, they need to have balance.

    Thanks for the comments.

    Mike
     
  8. Oct 8, 2010
    dvw86

    dvw86 Member

    Eastern Washington
    Joined:
    Sep 23, 2007
    Messages:
    191
    Just off hand I'd say that you were on the right track. I've seen CJ3Bs on CJ5 frames (CJ5 is about3" longer in the rear). They made up the difference by making a bumper out of the extra bit of frame sticking out the back. It looked good.
    [​IMG]

    [​IMG]

    A friend of mine put a flatty on a 1973 (long nose) CJ5. He cut the hood and fenders in half width wise and installed more material to stretch them out. They were fiberglass but the same would apply for steel. It looked really good as well. Just don't do this:
    [​IMG]
     
  9. Oct 10, 2010
    J Michael

    J Michael Member

    Burney, CA
    Joined:
    Sep 14, 2010
    Messages:
    151
    My wife and I spent the weekend in The City of Mt Shasta this past weekend and came across a custom 4X4 shop that had a early model CJ6 on their lot. It gave me a chance to get a good look at one. Jeep made the stretch from a CJ5 to the CJ6 right behind the door and in front of the rear wheel well. It didn't look so bad as I thought I remembered. I might have to give that idea a little more consideration. The good part about that idea is, it allows me to use a stock soft top door with a stretched tub.

    Mike
     
  10. Oct 10, 2010
    all4jpn

    all4jpn Member

    fredericksburg,va
    Joined:
    Dec 16, 2006
    Messages:
    363
    you could use the stock soft top and put a removable bulkhead and just have a mini bed behind the end of the softop..always wanted to see a 6 like that
     
  11. Oct 11, 2010
    J Michael

    J Michael Member

    Burney, CA
    Joined:
    Sep 14, 2010
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    151
    I was thinking of leaving out the new bulkhead and leaving a mini bed, this would allow more room behind the front seats for rear seat leg room.

    Mike
     
  12. Oct 17, 2010
    PbBelly

    PbBelly delinquent miner

    Central MO
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    Sep 13, 2009
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