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Dad's Flatfender

Discussion in 'Builds and Fabricators Forum' started by Fireball, Feb 6, 2020.

  1. Feb 7, 2020
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Pullman, WA
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    OK, and the answer is.... A home made full-time 4wd conversion for the Dana 18.

    My Dad never liked that being in 4wd causes slippage around corners. Especially in slick conditions. So... he took machine shop night classes at the local community college and built his own center differential conversion from scratch. It's been in the Jeep and functioning for 40+ years now. It's very clever. High and low range still work and the 2wd/4wd lever locks the center diff.

    Here's a drawing of a stock Dana 18 (I apologize for the quality, the paper copy hasn't survived well):
    [​IMG]

    And here's the full time setup (which thankfully has survived much better):
    [​IMG]

    The basic rundown:
    • He used a piece of pipe for the housing.
    • He made a cap for the housing that has bearings for the new output shaft and the new differential case.
    • He machined a custom differential case that replaces the rear output shaft in the lower part of the Dana 18. It still uses the stock low range slider gear and 2wd/4wd shift collar.
    • The spiders are Dana 25 parts. He made a custom cutter for machining the spherical pockets.
    • The front output shaft spider gear has a smaller hole because of shaft size limitations. He initially made a sleave, splined inside and out to take up the space but it didn't hold up. He then had a machine shop weld up the gear and cut new splines from scratch.
    • He made a custom rear output shaft, but used the standard output housing, speedometer gear and yoke.
    • As noted before, the custom front output shaft needed to be small, but has held up well. Realistically, it should. The jeep has 4.88 gears and the same Dana 25 parts in the axles. That means these components in the transfer case will only see about 1/5th the torque that would break an axle first.
    • The 2wd/4wd shift collar works as it did before, but now it locks the front output to the differential case for locked 4wd.

    He made it so no modifications were done to the Dana 18. He was worried it would break and wanted the ability to put the Jeep back to normal quickly.

    With the CV joints in the front axle and the center diff, it's always in 4wd and drives fantastic in slick conditions. Just like a Subaru. It's also surprising how little you need to lock the center diff when offroading.

    He said you're all free to use his plans royalty free if you want to make your own.

    ....and the box on the front axle was an attempt at locking differentials back in the 70s. It worked similar to the diff lock above. He extended the splines on the left axle shaft and had a cable actuated collar with internal splines and a dog clutch on the end. He cut a matching dog clutch into the end of the differential case for the collar to lock into. He tried it once in the back yard on wet grass and it took the dogs right off the differential case. He though about having a hardened sleeve welded into the case and using more and finer dog teeth, but never got around to it. Neat idea though!

    Well, that sums up the build. Hope you enjoyed it.

    It's a pretty neat old Jeep that got a lot of Jeeping use in the 70's and lots of tractor use ever since. Even though it's low and has open diffs, it always did well on the trails. With the tires aired down, it's flexy enough that it always seems to have all 4 tires on the ground. Of course, nobody was doing modern style rock crawling on the Pacific Northwest trails back in the 70s.

    I'll try to get some under hood pictures when I'm out visiting in the late spring.
     
    Last edited: Feb 7, 2020
    Muzikp, fhoehle, Rubicloak and 15 others like this.
  2. Feb 7, 2020
    txtoller

    txtoller Member 2021 Sponsor 2020 Sponsor

    Weatherford, TX
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    That is SKOOKUM!
     
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  3. Feb 7, 2020
    Rich M.

    Rich M. Shoe salesman

    Maryland
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  4. Feb 7, 2020
    wheelie

    wheelie beeg dummy 2021 Sponsor

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    Far out! Your old man is a sharp cookie. I'm liking this thread.
     
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  5. Nov 16, 2021
    homersdog

    homersdog Tulsa, Ok 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Tulsa, OK
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    :clap: Amazing!
     
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  6. Nov 16, 2021
    3b a runnin

    3b a runnin Active Member 2021 Sponsor 2020 Sponsor

    virginia
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    Hadn't seen this before, thats good stuff.
     
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  7. Nov 16, 2021
    Chilly

    Chilly Active Member

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    The rarest Super Jeep. 1 of 1.
     
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  8. Nov 16, 2021
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Pullman, WA
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    It's a great time capsule of a 70's wheeling rig ...with a few special items. I'm visiting home this weekend and will try to get some pictures under the hood.
     
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  9. Nov 17, 2021
    Cunder_Tunt_559

    Cunder_Tunt_559 New Member

    FRESNO
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    i would LOVE detailed drawings and measurements of that 4WD/AWD conversion for the Dana 18 so i can put it into solidworks 3d.
     
    Fireball likes this.
  10. Nov 17, 2021
    Buildflycrash

    Buildflycrash Blind and Dirty 2022 Sponsor 2020 Sponsor

    Gulf Breeze FL...
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    And now we know where Fireball got his smarts from...
     
  11. Nov 17, 2021
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Pullman, WA
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    The drawing above is to scale, and the bearings are known sizes, so it shouldn't be too hard to duplicate. Having some example D25 parts would help too.
     
  12. Nov 17, 2021
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Pullman, WA
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    Here's a link to the full size scanned drawing: new18case.jpg
     
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  13. Nov 17, 2021
    Jw60

    Jw60 Member: Club Foot Dad Club. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Sedalia MO.
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    I figured I would eventually follow up with jpet on his d18 model he used for the 5.13 gearset. He asked what file type I needed but we both been busy. I would think if one were to do this now the use of dana 30 components would allow for a torsion center diff or air locker.
     
  14. Nov 17, 2021
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Pullman, WA
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    A Torsen gear set would be the bomb. It's already simple to lock as is so I don't thing an air locker buy you much.
     
  15. Nov 17, 2021
    47v6

    47v6 junk wrecker! 2021 Sponsor 2020 Sponsor

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    porn. straight porn.
     
  16. Nov 17, 2021
    timsresort

    timsresort Member 2021 Sponsor

    South Lake Tahoe CA
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    Very cool, I had not seen this. Your dad had some great ideas. I can still hear my dad "bench racing" with his buddies over some beers around the campfire. And yes, apparently at least some does rub off on us kids.
     
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  17. Nov 18, 2021
    givemethewillys

    givemethewillys Been here since sparky ran it. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    New Kent, VA
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    Wow, this is the first time I'm seeing this jeep. Love it.
     
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  18. Nov 18, 2021
    Jw60

    Jw60 Member: Club Foot Dad Club. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Sedalia MO.
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    This would allow 2wd rear only again.
    Original front output stub. Splines on the tip of the front output to match mainshaft.
    Shift rail would need another detent halfway engaged for 4wd.

    [​IMG]20211118_140042 by Joe with a jeep, on Flickr
     
  19. Nov 18, 2021
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Pullman, WA
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    Yes that could work.
     
  20. Nov 18, 2021
    Norcal69

    Norcal69 Out of the box thinker 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Something like this would outweigh the downfalls of the D18!
     
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