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Technical Death wobble

Discussion in 'Traditional Hot Rods' started by Hildy56, Mar 1, 2024.

  1. DDDenny
    Joined: Feb 6, 2015
    Posts: 20,008

    DDDenny
    Member
    from oregon

    Dead perch.

    20181124_125328.jpg
     
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  2. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,607

    2OLD2FAST
    Member
    from illinois

    Don't believe that's necessarily the cause of the man's
    DW , wandering , yes !
     
  3. flynbrian48
    Joined: Mar 10, 2008
    Posts: 8,440

    flynbrian48
    Member

    He took the dead perch out, so without that it has to have a Panhard bar. Or, put the dead perch back in, one or the other.
     
  4. Joe H
    Joined: Feb 10, 2008
    Posts: 1,655

    Joe H
    Member

    Can you explain Dead Perch? I think I know what it is.

    Also roll the car forward at least one or two tire rotations before you check toe-in, it makes it " as driven " removing all slop in all joints.
     
    alanp561 likes this.
  5. alanp561
    Joined: Oct 1, 2017
    Posts: 4,954

    alanp561
    ALLIANCE MEMBER

    Borrowed from @Frames. No shackle on one end of the spring.
    [​IMG]
     
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  6. Boneyard51
    Joined: Dec 10, 2017
    Posts: 6,548

    Boneyard51
    Member

    Ok, just the facts! To quote Jack Webb! If you have a straight axle and get the wobble, the very first thing you need to do, is check for worn suspension components. With worn suspension components,alignment means nothing! Once you insure all your suspension components are in good shape, set your alignment to specs! This needs to be done anyway! If you still have the problem, check to make sure your wheels and tires are round, in line and balanced! If you still have the wobble after all this and everything appears to be perfect, take out, or put in a few degrees caster toward the edge of specs or even a degree or two out of specs. This will stop the wobble!
    Trying to fine the cause of the wobble, can be impossible! Believe me it can hide! But the above procedure will stop the wobble! After you stop the wobble, then add the dampner for insurance! Never put one on to stop the problem, fix the problem first!





    Bones
     
  7. twenty8
    Joined: Apr 8, 2021
    Posts: 2,792

    twenty8
    Member

    That's unusual. It is not often that scrub radius is described using a diagram showing positive camber...:confused:o_O
     
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  8. Budget36
    Joined: Nov 29, 2014
    Posts: 14,298

    Budget36
    Member

    So crosssteer needs a pan hard rod?

    Early Fords didn’t use them, I think maybe until ‘39 or so. Were the earlier ones subject to wobble?
     
  9. twenty8
    Joined: Apr 8, 2021
    Posts: 2,792

    twenty8
    Member

    Last edited: Mar 2, 2024
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  10. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 13,354

    Johnny Gee
    Member
    from Downey, Ca

    There’s not too many images that I could find so I cut out a portion of the original image because there wasn’t many, make if any illustrations showing a solid axel. Just concern one’s self with king pin center line in relation to center line of the tire where it meets the pavement.
     
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  11. twenty8
    Joined: Apr 8, 2021
    Posts: 2,792

    twenty8
    Member

    Yep, I know how it works. Just don't see it illustrated as positive camber often.
     
  12. don colaps
    Joined: Nov 29, 2007
    Posts: 172

    don colaps
    Member

    But seems legit since we’re talking Model A Ford
     
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  13. don colaps
    Joined: Nov 29, 2007
    Posts: 172

    don colaps
    Member

    I’d say Ford introduced panhard rods when they changed the spring design from preloaded to non preloaded? Or just when they went from side steer to cross steer in 1935?
     
    Last edited: Mar 2, 2024
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  14. 1946caddy
    Joined: Dec 18, 2013
    Posts: 2,167

    1946caddy
    Member
    from washington

    Bought a wrecked jeep (sheet metal) and installed a 4" lift kit along with 12" wide wheels and tires. Couldn't get over 20 mph without a horrible death wobble.
    Took it into the alignment shop and he couldn't find anything wrong. All the tie rods ends were tight and steering dampener was good. Good alignment.
    I replaced every tie rod end and a new steering dampener. I couldn't find a problem with the old parts.
    Put rig back on the ground and took off down the road, hit 20 mph and no more death wobble. Up to 60 mph, no problem. I can drive up to 70 plus mph without any problem.
     
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  15. Budget36
    Joined: Nov 29, 2014
    Posts: 14,298

    Budget36
    Member

    I don’t know. I had a ‘39 rear, clutch brake pedals in a ‘36 PU. Also in the bed was the front bar as well, so I’d just assumed it all came from the same vehicle, hence why I mentioned ‘39. But I’m no expert at all.
     
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  16. don colaps
    Joined: Nov 29, 2007
    Posts: 172

    don colaps
    Member

    I’m no expert either, for sure. I edited my post tvough
     
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  17. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 13,354

    Johnny Gee
    Member
    from Downey, Ca

    This is why I asked if toe “out” would get worse if one were to roll the axel back for more caster.

    Op has said he never checked his toe.
     
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  18. ronzmtrwrx
    Joined: Sep 9, 2008
    Posts: 1,269

    ronzmtrwrx
    Member

    My 39 never had a panhard bar. Front or rear. I thought they came along in 41, but I'm no expert either. lol
     
  19. Budget36
    Joined: Nov 29, 2014
    Posts: 14,298

    Budget36
    Member

    lol. Like I mentioned, the PU I had was with ‘39 parts and the bar was in the bed.
    So I did the ASSUME thing, obviously I was the ASS. ;)
     
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  20. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 3,202

    Kerrynzl
    Member

    Early Fords had Triangle Shaped ["A" shaped] bones., not split bones
    And also the correct shackle angle
    As soon as the wheel gets "re-invented" by splitting the bones, and reverse eye the crossleaf [so the eyes are on the outer side of the arch] the problems start.

    Scrub radius is a factor of king pin inclination not camber. Smaller rolling radius increases scrub radius unless positive offset wheels are used to counteract this

    A dead-perch is a classic example of "Silver wiener syndrome" [If a winning racer glues a silver wiener to his car, all the Hot Rodders and Street Racers would do the same.]

    The dead perch was an early Sprintcar and Midget technique where they're are constantly fighting a losing battle with weight.
    The Cross leaf doubled as a panhard bar, and used in conjunction with cowl steer so it didn't cause bump steer..

    On left turning cars the dead perch was always mounted on the L/H side to keep the leaf under lateral tension. This also cause the L/F wheel to "grab air" which didn't matter.
    R/H dead perches would result in an undesirable jacking effect on L/H corners.

    A dead perch is not overly desirable with cross steer, because it is almost impossible to engineer out mechanical. bump steer. The axle will arc basically 1/2 the spring width. whereas the drag link is much longer.
    If somebody insists on a dead perch, the perch must be on the opposite side of the steering box [passenger side]

    A L/H dead perch with a L/H steering box causes the axle and steering to arc in opposite directions.

    A panhard bar is far superior with a cross steer because it can mimic the arc of the drag link..
    Any driver who is capable of driving at the limit of tyre adhesion would certainly notice the flaws in a dead perch / cross steer combination.
     
    Last edited: Mar 2, 2024
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  21. DDDenny
    Joined: Feb 6, 2015
    Posts: 20,008

    DDDenny
    Member
    from oregon

    Which always begs the question "is that sitting in the driver seat or facing the front of the engine"?
    Now that I think about it....is it LHD (normal):eek: or RHD (across the big water).
    What say you @Kerrynzl
     
  22. 4bangerbob
    Joined: Jun 29, 2013
    Posts: 142

    4bangerbob
    Member
    from AB, Canada

    ford introduced the panhard bar in 1942. Cross steering in 1935.
     
  23. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 13,354

    Johnny Gee
    Member
    from Downey, Ca

    Good question @DDDenny IMG_2521.jpeg

    The real answer is from the drivers seat facing forward naturally.
     
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  24. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 3,202

    Kerrynzl
    Member

    Across the big water, steering on the Right side .... is the right side But in the USA steering on the Left side .... is the right side :D:D:D
    But to add to the confusion
    Driving on the left side .... is the right side But in the USA driving on the right side .... is the right side

    It is a simple concept to overcome, Just get a single seat open wheeler and apex the corners [road rules don't matter]
    upload_2024-3-3_14-30-33.png
     
  25. X-cpe
    Joined: Mar 9, 2018
    Posts: 2,084

    X-cpe

    Was always taught that L/H vs R/H was determined with your butt parked in the driver's seat. Told my students that when dealing with customers, use drivers side or passenger side because most customers were smart enough to not screw that up.
     
  26. DDDenny
    Joined: Feb 6, 2015
    Posts: 20,008

    DDDenny
    Member
    from oregon

  27. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 13,354

    Johnny Gee
    Member
    from Downey, Ca

    No smoke and… IMG_2522.jpeg
    on my part. ;)
     
  28. ronzmtrwrx
    Joined: Sep 9, 2008
    Posts: 1,269

    ronzmtrwrx
    Member

    Ha haa, I wouldn't have argued with you either way. Looks like we both learned something.
     
    Budget36 likes this.
  29. DreamerJ
    Joined: Oct 3, 2021
    Posts: 116

    DreamerJ
    Member

    Try an Adjustable spring perch after your measurements are correct and it still occurs. I believe they allowed my spring to travel in more up and down path than a fixed perch.
     
  30. Left or right doesn't matter where the driver sits. It's left or right as the car faces forward, same as a person.
     
    29A-V8 and 26 T Ford RPU like this.

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