Register now to get rid of these ads!

Dead mans purch

Discussion in 'The Hokey Ass Message Board' started by ratrod0, May 5, 2012.

  1. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,903

    need louvers ?
    Member

    It doesn't seem that it can make the spring a panhard bar, it does. Ford actually had a much "looser" interpation of this idea when the original cross spring suspension was designed by putting the spring itself in a minor tension that kept the shackles at a 45 degree or slightly shallower angle. This basically turns the spring its self into a locating device. Racers later figured out that positively locating one end of the spring, the same side as the steering box made that locating device, well, more positive.

    With a properly made dead perch there won't be any need to shorten one side or the other to compensate because the perch itself is made in such a manner to Mimmic the shackle angle of a properly set up twin shackle set up.
     
  2. fiftyv8
    Joined: Mar 11, 2007
    Posts: 5,394

    fiftyv8
    Member
    from CO & WA


    Green - confirms spring can be used as a panhard bar.
    It is a personal opinion whether it is suitable for street use.

    Blue - does not compute since any vehicle running rear semi eliptic springs would not be viable if what is said is fact.
     
  3. Andy
    Joined: Nov 17, 2002
    Posts: 5,117

    Andy
    Member

    I have an old Deuce Factory dead perch if interested. Never used. PM me

    PS I have used a home made one for 20 years and love it.
     

    Attached Files:

  4. jdsludge
    Joined: Sep 2, 2011
    Posts: 49

    jdsludge
    Member

    Looks like Ive got to move my dead perch to the driver side.
    I mounted
    One on the passenger side and probably would have left it there if it weren't
    for this thread! Thanks guys for all the input!:)
     
  5. Steel A Rod
    Joined: Jun 28, 2010
    Posts: 265

    Steel A Rod
    Member

    That's funny!!!
     
  6. No, the difference is on a semi elliptic spring in a rear suspension, one end is fixed and the other end is movable via the Shackle. In the case of the dead perch, on end is fixed (the perch) and the other end (which is effectively the center of the spring) is ALSO fixed as it is bolted solid to the crossmember. So what happens is, as the springs compresses and flattens out, Thereby becoming longer, the entire axle assembly shifts to the side of the dead perch. Panhard bars do this as well, but in a much lesser arc as they are much longer. The spring is compounding this action by not only being shorter between the two pivot points but is also becoming longer as it flattens out.
     
  7. No, the length and location of mounting of the dead perch is figured in when manufactured to equal the spacing of the shackle side
     
  8. DICK SPADARO
    Joined: Jun 6, 2005
    Posts: 1,887

    DICK SPADARO
    Member Emeritus

    Aahhh Grasshopper HRD, no function datway. I know some of you are in love with dead perches but they are race car parts not street car parts. Many of you have adequate operation with them because of very limited travel of suspension however as you try to soften the ride up the use of the dead perch is not advised.
    The major concern is the spring bind on the fixed side of the spring and the offset action created by the arc of the spring during compression. This is not the same action on the rearend although the mounting principle is the same, the rear is longitudinal deflection rather than lateral deflection and the movement is registered thru the rear axle not the frame. Before this stinks up anymore here is a scan of what is going on.
     

    Attached Files:

  9. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    Good info hotroddon, sometimes the perceived "cool part" factor outweighs the practical factor in the pieces a guy buys for his street car and while this probably does what it's designed to on a circle burner it doesn't appear to be optimum for the street.

    Thanks for the drawing Dick and the explanation
     
  10. You are saying the same thing I did. That the spring is causing offset action created by the arc. That's what I said in slightly different terms :rolleyes: I am agreeing with you. I think the Arc is actually even greater than you illustrated as the spring doesn't Pivot. but flattens out as it travels upward making it effectively longer the more it travels.
    As for Spring bind, I'm not sure I totally agree with you there - the spring isn't really "Binding" so much as it is pushing the axle assembly outwards during compression. That might cause a slight amount of stiffness based on more parts having to move, but in reality, having driven a coupe of cars back to back before and after the Dead perch installation, I could never feel any difference in stiffness of the car during bump, but if you are tuned into it enough you can definitely feel the car push slightly to one side and back. If there weren't a shackle on the other side allowing the axle to travel sideways, then it would definitely bind, becoming almost rigid.
    Although I have used them in the past, they are not my first choice, but in our very limited travel Hot Rods, they don't work all that bad in the real world.
     
  11. fiftyv8
    Joined: Mar 11, 2007
    Posts: 5,394

    fiftyv8
    Member
    from CO & WA

    Agreed half the length of a transverse spring is hardly a suitable length for the perfect panhard bar.

    Question is if a dead perch is fitted and it is having a panhard bar effect, which side of the front axle should it be fitted to.

    My belief is that like it or not as this combination has a panhard bar effect the dead perch should be fitted to the passengers side (to match with cross steering) for street use.
    In saying that, I know it would probably work on either side just as badly (with different steering setups), but taking into account the fact that a rear panhard bar may also be fitted on some hot rods and it is more than advisable to ensure both parnhard bars (or effect there of) are working in the same plain and not opposing which will cause a sissor effect, which to my mind is down right dangerous under some road/driving situations.
     
  12. SimonSez
    Joined: Jul 1, 2001
    Posts: 1,637

    SimonSez
    Member

    Yes, agree that the Dead perch (if fitted) should be on the passengers side with cross-steer.

    Now you can see why Deuce Factory stopped selling them :)



     
  13. R Frederick
    Joined: Mar 30, 2009
    Posts: 2,658

    R Frederick
    Member
    from illinois

    [​IMG]
    :D
    Mine are both live, never had a problem.
    Problems start to happen when you start to bind up working parts, puts more stress on everything else.
     
  14. I'm confused (nothing new), so many differing opinions. I've been running one on my coupe on the passenger's side for about nine years.

    Also, the product that So-Cal sells is an adjustable dead perch. I didn't notice any mention of that in this thread yet. The swivel helps alleviate the spring bind.
     
  15. Andy
    Joined: Nov 17, 2002
    Posts: 5,117

    Andy
    Member

    They work better with a flat spring and a reversed eye. As Dick's diagram shows, if the spring has a lot of arch and the spring eye is way below the center of the main leaf. you get a bit of sideways movement. I never had a problem with my set up as my spring is essentially flat and does not move the eye in or out with deflection. I have worked on my car for a long time by varing spring rates and roll stifnesses. It handles very precisely with the dead perch. It is like most things. It all dependes on the details.
     
  16. BLACKNRED
    Joined: May 8, 2010
    Posts: 366

    BLACKNRED
    Member

    Listen to what Dick Spadaro and Hotroddon are saying.

    Dead Perches do not work if you have any suspension movement.

    spend the extra $ 5.00 and use a panhard bar. you won't regret it.
     
  17. Atwater Mike
    Joined: May 31, 2002
    Posts: 11,625

    Atwater Mike
    Member

    Carl Fjasted told me the 'improper' way these were being used. Some golden-eagle street rodder used one at each end!
    Deuce Factory discontinued them, sold the lot off to a rod shop in O-Z.
    (I had to order 2 of them indirectly from Australia to get them)

    Magnum picked up the option, and made them again. So did So-Cal; but all 3 types are different.
    Two of them don't mimic the geometry of the shackle on the other side; so the spring main leaf is different left-to-right.
    I think the So-Cal one was correct. (my son and I have them, in stainless...I've made them before, used them on everything I've ever built. Reversed eyes and flat leaves, yes.)
    Those 'adjustable' perches are bandaids for chassis with incorrectly castered cross members.
     
  18. I've had one on my 27 for ten years now, the car rides good , handles good ,I'm very pleased and no I would not put an ugly ass panhard on my car... Or a vega box... Or any other street rodder crap.
    1) tie rod
    2)cross steer
    3)panhard
    That looks like a harp! Yuch.
     
  19. Avgas
    Joined: Dec 31, 2007
    Posts: 282

    Avgas
    Member

    I believe that a dead perch disguises another problem with in the front suspension! Transverse springs pivot thru the chassis centerline & dissipate the energy transmitted thru that spring transversally. When one side of the spring is in bind the suspension is not working, factors effecting the supposed need for a dead purch may be ineptly long shackles, larger tire foot print on the road surface, toe in ir caster adjustment or poor design geometry, address the problem, install a correctly designed spring pack & enjoy the ride!
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.