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Technical rear radius rods and a torque arm

Discussion in 'Traditional Hot Rods' started by Model A Mark, Nov 17, 2019.

  1. Model A Mark
    Joined: Apr 30, 2008
    Posts: 1,264

    Model A Mark
    Member
    from dallas
    1. Holley 94 Group

    Hey guys, Im thinking about using the piece I cut off when I split the front wishbones, to attach the rear radius rods together and then using that ball and socket joint to attach the the radius to the cross member .
    Sure would articulate good, but would it hold up ?
    Running a blown flathead .
    Thanks for the ideas ..
     
  2. The concept is good, but the radius rod are not strong enough for this duty. You can beef them up or add a torque arm to take the load. The torque arm would replace the function of the original torque tube.
     
    lothiandon1940 likes this.
  3. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member

    You apparently are talking open drive conversion?

    on the daily driven 32 with souped up Olds Rocket/stick trans/Olds rear, I used 35/36 trailing arms tied together at front with a 32 wishbone yoke, and...no torque arm. 35/36 are the best by far, for strength. The car has been beat on fiercely back when first built 3 years back, but it has skinny bias. Slicks & serious racing would justify a torque arm.

    I would not trust 33/34 rear arms for open drive even with twin torque arms, I had a 34 set and they are just look too wimpy as far as their design.
     
  4. alchemy
    Joined: Sep 27, 2002
    Posts: 14,722

    alchemy
    ALLIANCE MEMBER

    My brother's A pickup has had this setup with 36 wishbones for over a decade. His is behind a fire breathing 312 that has made numerous passes down the track at Mokan.
     
    kidcampbell71 and lothiandon1940 like this.
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  5. Model A Mark
    Joined: Apr 30, 2008
    Posts: 1,264

    Model A Mark
    Member
    from dallas
    1. Holley 94 Group

    Thanks guys, Im running 35/36 radius rods, and do plan on running a torque arm..
     
    lothiandon1940 likes this.
  6. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,463

    sunbeam
    Member

    It's not how much motor but how much traction.
     
  7. Kiwi 4d
    Joined: Sep 16, 2006
    Posts: 2,557

    Kiwi 4d
    ALLIANCE MEMBER

    Its not even traction that causes rear movement. Our 32 with open drive 35/36 split radius rods and a decent torque arm attached to a truck size tie rod end. The tie rod nut came slightly loose on a long road trip and every time we let off the gas we could hear a little knock. Put the car on a lift and put a rattle gun on the nut , problem gone.
    What i am saying is just because nothing has broken with no torque arm yet, doesn’t mean it wont.
     
  8. If you want to be totally sure that the wishbone will stand up to it, you can make them into a ladder bar with a piece of tubing welded to the top of the wishbone and then attached at the other end on top of the rear axle. Look at how my buddy @hotrodderhaag did his on his 32 three window. plenty beefy, worked great and look killer.

    Bens ladder Bars.jpg 3b02daa7961b36dbebc6e6eb6f46f11b.jpg
     
    brEad, bct, Blues4U and 3 others like this.
  9. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member

    You said they are split, and anytime the front ends are not articulating from one precise point like a wishbone ball, then you have stresses that simply don't exist with using a center ball.

    you proved it when saying a nut loosened up.

    There is an old thread here where HarmsWay asked for photographic proof of 35/36 arm failures that never used a torque arm. Pages later, no one could. There was one pic showing totally rotted out arms that did fall apart the forged ends, it was paper thin and full of rot holes. Another lame pic showed arms bent sideways on a chassis that was pushed around in a junkyard by a dozer.

    .
     
    Kato Kings and alchemy like this.
  10. Pitbullgoingpostal
    Joined: Jan 2, 2009
    Posts: 408

    Pitbullgoingpostal
    Member

    Can someone provide more pictures of torque arm setups please?
     
  11. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,737

    thunderbirdesq
    Member

    Here’s a few I’ve done
     

    Attached Files:

    brEad, mgtstumpy and Nailhead Jason like this.
  12. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 7,722

    mgtstumpy
    Member

  13. BobPer
    Joined: Feb 15, 2009
    Posts: 281

    BobPer
    Member

    I agree with F&J about a single front pivot point being the best (if not possible than be as absolutly close together as you can to minimize binding). Also the longer the arms the better to minimize pinion angle change (mine are stock length with the torque arms being the only new welding). I am using an open drive 47 truck rear (hope to use a quick change in the future), an open drive 3-sp, 35/36 radius rods, added 1" DOM tube torque arms, homemade brackets, Johnny Joint, and model A or T rear spring. The rear crossmember is Model A on my homemade frame (Dadgum frame). I'm using a coupling nut which will be welded on both sides of my center crossmember with the jamb nut. I still need to complete all the welding but here are some pictures so far. Bob
    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]

    radius rods 1.jpg
    radius rods 2.jpg
     
    Last edited: Nov 22, 2019
  14. Model A Mark
    Joined: Apr 30, 2008
    Posts: 1,264

    Model A Mark
    Member
    from dallas
    1. Holley 94 Group

    that looks good bob
     
  15. Gary Addcox
    Joined: Aug 28, 2009
    Posts: 2,216

    Gary Addcox
    Member

    Your setup looks plenty strong and well designed. I'm sure old Henry would balk, but Edsel would certainly approve.
     
  16. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,594

    thirtytwo
    Member

    53FAFECA-2846-42B3-BB52-5A12CA77A115.png Considering the gusset is mounted on center of the housing I don’t think much triangulation strength is added in this setup
     
    brEad likes this.

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