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Hot Rods Broken spring pivot bolt

Discussion in 'The Hokey Ass Message Board' started by 2OLD2FAST, Jun 29, 2015.

  1. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,992

    2OLD2FAST
    Member
    from illinois

    Saturday , 10 miles from nowhere , the left front spring pivot bolt [ bolt welded to tube that connects the shackle to the batwing] broke/sheared... this is the second time in 40K miles ... This is pretty much the common way of doing it on a Tbucket w/spring behind...the first 1 that broke was from speedway, this 1 I welded {replaced both sides], so it's not a faulty part I believe..anyone else have this problem ?? AFA I can tell there's no binding or mis-alignment....first one that broke was passenger side , this time drivers side... any thoughts ????
    dave
     
  2. Atwater Mike
    Joined: May 31, 2002
    Posts: 11,618

    Atwater Mike
    Member

    Hi, 2old... Did it break right on the weld, or right next to it?
    Also: What was the bolt shank diameter, and finally, was the bolt an Allen type head that had been 'fish-mouthed' to fit to the tube?
    Best application I've seen was a 3/4" hard bolt shank (grade 8, SAE thread black finish) tig welded to 4130 tubing: after welding, heat treated to 700 degrees, (normalized) and allowed to cool slowly, in the oven preferably.
    Some ditz told me "That's 'overkill'." Hah! Not when I've seen 'em break...
     
  3. Hey, isn't that set up called a suicide front end?

    image.jpg

    image.jpg

    So it's the second or lower pic of the style you're breaking?
    And the first or upper pic is the design the Henry came up with.

    Henry pins are 0.75 at the narrow part and forged. The upper part is considerably thicker. Henry part is loaded considerably different too.

    Does it Seems strange that the little shackle bolts hold up the car?
    Does it really seem strange that the 1/2" Or 5/8 stud welded onto 1/8" wall tube fails? The OD of those hangers can be a bunch bigger increasing the wall thickness. A bigger stud can easily be put on there with a bigger OD. Any bottoming out transfers any additional jounce to the pee-pee stud.

    Pics of your set up would help figure it out. If your certain its not parts then its setup.
     
    saltflats likes this.
  4. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,992

    2OLD2FAST
    Member
    from illinois

    Very similar to the 2nd pic..bolt in both cases has sheared were the shank meets the head... they are /were grade 8 bolts , hex head w/the head shaped to fit the tube...they are what speedway used to use [as well as others]...I agree that there should be a better way.....I've seen some on epay that have a piece of tubing welded to the shackle tube that appear to be tapped internally so the weight is born by the tube and not by the bolt...
    dave
    dave
     
  5. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,576

    Dan Timberlake
    Member

    Can you post a picture of the fracture surfaces?
    I'm expecting they look something like this -
    http://news.sherrylabs.com/laboratory-news-article.php?news_id=44

    The weight of the car is trying to bend the bolt, and the stress is highest right in the threads as they enter the nut.
    When a stud is going to be subjected to bending, at the very least it should not be threaded where it is restrained.
    http://www.maxchevy.com/tech/2008/iii_4-head/MaxChevy-409-08.jpg

    Better still is for the stud to flare out to form a flange that is tightened hard against the supporting surface.
    http://www.grumpysperformance.com/STUD-18.jpg

    I'd remove the inner nut and replace it with a tapered spacer, then tighten the outer nut hard.
    Then the bolt would not be subjected to bending any more.
     

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  6. Katuna
    Joined: Feb 25, 2005
    Posts: 1,822

    Katuna
    Member
    from Clovis,Ca.

    That's a shit design with the jam nut on the pivot side. Designed to fail. The threads have already started the failure process by weakening the stud. Definitely should have a solid shoulder and shaft through the wing.

    Of course none of the pontificating does you jack shit when you're stuck on the side of the road. It falls under the "no shit, Sherlock" response.
     
  7. 3quarter32
    Joined: Dec 10, 2010
    Posts: 603

    3quarter32
    Member

    Would the stainless units be any better? I have similar, but without the jam nut on the spring side like the one shown.
     
  8. Maybe welding it is the problem? Try using one that isn't welded.
     
    saltflats likes this.
  9. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,992

    2OLD2FAST
    Member
    from illinois

    In responce : mine does NOT use the inside jamb nut , head pulls up tight to the batwing ... speeways stainless offering is "investment cast" ...didn't exactly instill confidence.. P&B , what do you suggest , super glue ????? LOL
    dave
     
  10. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,476

    woodiewagon46
    Member
    from New York

    I think your problem is with the jam nut. I can see a couple of exposed threads which will break under up and down flexing of the spring. I think if the fitting was pulled up tight it would help. No to the stainless steel, it is softer than what you have now.
     
  11. Ok my dumb I didn't catch where it was breaking. I think I have some that were forged in the garage, like originals. Maybe that is the way to go, they would be hard to find maybe. I don't think that original Ford perch bolts were welded or investment cast. I'll try and give mine a close look when I am out later and let you know what I figure out.
     
  12. alchemy
    Joined: Sep 27, 2002
    Posts: 22,305

    alchemy
    Member

    Find an original Model T one. Forged by Ford. Gotta be stronger than some undersized Chinese steel. I think they might be from the rear axle?
     

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