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spring behind and death wobble?

Discussion in 'The Hokey Ass Message Board' started by alteredpilot, Nov 3, 2011.

  1. i did a bunch of searching and still haven't seen a definitive answer.

    is there anything inherent to a spring behind design that makes a vehicle more prone to death wobble.

    why i ask....
    if my roadster pu doesn't sell in the next week, i'm going to build a new frame to get the car sitting a little more how i want it.

    presently the spring is mounted to the wishbones about 7" behind the axle.

    i kinda like the spring behind setup for ride height, but i'm wondering if i'm going to regret the dimensions later. in other words, do you think the axle is mounted TOO far behind?

    thanks.
     
  2. Retrorod
    Joined: Jan 25, 2006
    Posts: 2,018

    Retrorod
    Member

    My experience is that "death wobble" is more a function of lack of caster, excessive play in components and incorrect steering angles. I've driven all sorts of straight axle cars with different types of suspension and mounting methods that are just fine with the spring aft of the axle.
     
  3. We actually tried all that on the raven's roadster. It was jam up but still developed a death wobble @ 55-60. This year we pulled his engine and put my balanced engine in its place no more death wobble. I can't say that this will cure everyone's problem but it cured his after about 4 years.

    Altered pilot,
    I like to mount my sprind behind up close to the yolk, if you are using Ford radius rods they are not built to handle much stress. The farther you move the axle ahead of the spring the more stress you put on the radius rod.

    Just food for thought.
     
  4. cool.

    its weird. when this thing decides to go goofy, it doesn't seem to do what the other cars i've driven seem to do (extreme left to right). it doesn't transmit up to the steering wheel. its more like a bouncing oscillation left to right. (i think a wheel may be a little tweaked.). the front wheels seem to shimmy a little and then they just start bouncing like crazy. real fast like. so i was wondering if the placement of the spring in relation to the bouncing weight (front wheel assemblies) may be exaggerating the symptom due to some function of geometry.
     
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  5. Mike Moreau
    Joined: Sep 16, 2011
    Posts: 290

    Mike Moreau
    ALLIANCE MEMBER

    "Front end" problems can be caused by a whole bunch different conditions. Different people use different terms to describe the same symptom, which makes diagnosing a problem on the 'net difficult. Search for "DETH WOBBLE" (not death) and see what you learn. From what you describe, I think you may be experiencing "axle tramp" where the axle moves up and down like a teeter-totter. Different problem, different solution. Try switching wheels side-to-side, raise the car off the ground and grease it, Take it to a good front end shop and have them check the toe-in. (A professional toe-in adjustment on my "A" solved a frightening death wobble) You may get lucky. Please report what you do and how you solve your problem.
     
  6. LB+1
    Joined: Sep 28, 2006
    Posts: 569

    LB+1
    Member
    from 71292

    I seem to note that the speed is always about the same on the DEATH wobble
    I will go with Caster and a tire problem - king pin's side to side - Sounds crazy
    but put a sand bag (TIE) it own of say 35 lb on the spring and go try it
     
  7. okay guys...
    i'm not trying to cure my death wobble. i know what the problem is.

    lets stay on track.
    i asked if putting the spring that far back can add to any other potential for speed wobble, death wobble, wheel jounce etc.

    i think i got my answer.
     
  8. okay guys...
    i'm not trying to cure my death wobble. i know what the problem is.

    lets stay on track.
    i asked if putting the spring that far back can add to any other potential for speed wobble, death wobble, wheel jounce etc.

    i think i got my answer.
     
  9. LB+1
    Joined: Sep 28, 2006
    Posts: 569

    LB+1
    Member
    from 71292

    Duh - on me - What was the answer?
     
  10. morac41
    Joined: Jul 23, 2011
    Posts: 532

    morac41
    Member

    Hi Alteredpilot....Have you checked your king pin inclination..it should be at least 3 degrees to wards the back from the top..this will defiantly give the front end wooble..if it is vertical or leaning to front of axle ....Doug
     
  11. yekoms
    Joined: Jan 21, 2007
    Posts: 1,088

    yekoms
    Member

    Like was said before alot of things cause front end troubles...There seems to be a bunch of cars with a spring behind like yours and I don't think that they all have the wobble. I don't have the answer and I'm interested also. I have heard of guys havin' issues with out of round tires. Once they found a truck shop that could shave the tires to make them true they were OK. There was one size bias tire that was worse than others but I don't remember what size it was. Check with Clark or Scary Larry here on the HAMB.
    Smokey
     
  12. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,880

    Mr48chev
    ALLIANCE MEMBER

    I had the same symptoms with my T bucket with the spring over the axle and over the years thought it was due to either the wheels being out of balance and or having less than stellar shocks on the front. Looking back and looking at old photos I now realize that most likely I had way too much caster on the front axle the way I had things set up. I also didn't have the drag link parallel with the wishbones but that was 1974 Technology done by a 25 year old who thought he knew a lot more than he did at the time.
     
  13. TheTumbleweeds
    Joined: Jul 29, 2010
    Posts: 536

    TheTumbleweeds
    Member
    from Sweden

    [​IMG]I have same wobble on my hotrod in very slow speed...It freaks out!! AND also over 110 km/h, when hit a little hole on the ground, It flipps out, the front wheels is flying up´n down!! First experience was fippin over to other side of the road!

    Well, some answers is, I dont have any shock system in front, and no steering damper...

    I´ve bought knee shocks to buick 55, and vw steering damper. Should make it run good.

    Maybe Im wrong, maybe it works!

    Good luck anyway =)
     
  14. jimvette59
    Joined: Apr 28, 2008
    Posts: 787

    jimvette59
    Member

    Hey tumbleweeds I would be very leary of that front axle mount. Looks a little on the slim side, the axle looks like it will jump like a see saw. Just my opinion.
     
    Last edited: Feb 13, 2012
  15. TheTumbleweeds
    Joined: Jul 29, 2010
    Posts: 536

    TheTumbleweeds
    Member
    from Sweden

    [​IMG]Yeah...Its pretty rough buildt... Pekka the wizzard made the text on the hood side, and I realize, its a good point there.... Suiciadal tendencies!





    Maybe I have to look over the front end a little bit... =)
     
  16. the consensus seems to be that all other things being equal, the location of the spring shouldn't be that big a factor.

    thanks.
     
  17. pasadenahotrod
    Joined: Feb 13, 2007
    Posts: 11,776

    pasadenahotrod
    Member
    from Texas

    Caster at 5-7 degrees positive(top of axle leaned back), properly mounted and working hydraulic lever arm or tube(aeroplane) style shock absorbers, no play in kingpin bushings, shackle bushings, tierod ends, correctly balanced and ROUND tires, correctly adjusted steering box.
    With all of these items correct there should never be a death wobble.

    Steering dampeners on early hot rod front ends are bandaids, not cures for problems.
     
  18. Wildcycles
    Joined: Sep 17, 2007
    Posts: 335

    Wildcycles
    Member

    I have the "death wobble" problem with a 32 ford pickup I just bought yesterday!
    The previous owner told me about it before test drive and it happens at around 45-55 mph... Pretty nasty feeling the first time, so I am trying to find the cause and solve it... Mine can be brought on by hitting a bump, pothole or rough road and seems to be isolated to the right side. When it happens, it feels like the wheel is hopping... My axle is a chrome super bell tube axle.

    Does the fact that it can be brought on by hitting a bump narrow down the cause?

    Thanks for info
     
  19. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,927

    scrap metal 48
    Member

    Yes I agree.. Shouldn't be that big of a factor....
     
  20. jimvette59
    Joined: Apr 28, 2008
    Posts: 787

    jimvette59
    Member

    I put the front end together many years ago on the car in my avitar. Although I don't own the car any more. It never had a shimmy or a wobble or bump steering. You must go over the geometry it all matters. Google the word ACKERMAN. If you keep to the specs it will work.
     
    Last edited: Feb 13, 2012
  21. BLUDICE
    Joined: Jun 23, 2006
    Posts: 1,473

    BLUDICE
    Member

    My tbucket had the spring on top of the axle, and I got wobble running bias or radial, toe in or toe out, different air pressure, etc. I read everything on the subject. Then I read that Pete & Jake always installed a steering damper on all the cars they built. Well the way I see it if THEY recommend it who am I to question those two rodders? So I bought one and I no longer had to wear Depends any more. I can remember when some of our construction trucks - Ford F500 & F600 would wobble cause they all had straight axles too.
     
  22. I had that as well with the spring behind in my t. Check your tie rod. Is it properly sized? Should be at least 7/8 diameter. Also note if you have any bends in the rod. As son as you bend a tie rod it is no in pure compression and is much more subject to bending.
     
  23. Btw - The problem in my t was a wimpy 3/4 inch rod with heims. My buddy has a similar issue on his A and it was due to a small kink in his tie rod ( original ford unit). I felt smart when I figured that one out. :)
     
  24. spiffy1937
    Joined: Apr 9, 2006
    Posts: 729

    spiffy1937
    ALLIANCE MEMBER
    from Florida

     
  25. 201
    Joined: Dec 17, 2002
    Posts: 344

    201
    Member

    Tumbleweeds- in the side view of your car, looking at the spring eyes, it looks like you have some caster, maby not enough??
     
  26. I had what I would call 'axle tramp' on a spring behind 'T' and it turned out to be tyre pressure. So little weight on the front and I never thought to check. Turns out they like a lot of pressure, 32-35 psi.

    BTW, no shocks, ever. Worked well after pumping 'em up.

    Cosmo
     
  27. oldfordtin
    Joined: Feb 14, 2012
    Posts: 595

    oldfordtin
    Member

    Hello I had a track t with the same problem at about 45 I changed the rims and tires and it fixed the problem road smooth after that and if I tightened the friction shocks (real tight) it kept it from doing it when you hit a bump. I had two seperate isues
     
  28. SvenOla
    Joined: Aug 28, 2011
    Posts: 58

    SvenOla
    Member
    from Sweden

    "Alteredpilot" DON'T have a problem , he's just trying to prevent one .......
    Personally I don't think springlocation have too much influence in the problem ....
     
  29. striper
    Joined: Mar 22, 2005
    Posts: 4,482

    striper
    Member

    Tumbleweeds, please tell me that front spring isn't mounted just using the centre bolt.
     
  30. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member


    Holy crap, thank goodness for sharp eyed hambers.... Yes, it looks like just a centerbolt...and look at the reddish rust stains, just like the "moving" shackles....that red rust proves that center bolt is "workin" AKA it's MOVING!

    Edit... The few minutes of thinking about a single centerbolt mount; That bolt, even if grade 8 hardness will work inside the perch mount hole, and keep wearing away at the shank of the bolt right under the bolt head.

    Then when it gets thin enough there, as you take a roll in a turn, the "tipping" force applied to the spring and perch bolt, will certainly snap that bolt head off. Then as in any turn, the sideways forces on the front end, will cause the frame/perch to slide one way or the other....meaning a very quick sharp turn that you won't be able to react to, in time, to avoid a crash.
    Also, when the bolt head snaps off, the spring pack "unloading" will push the front of the frame up....man what a ride...
    Park that car before you kill an innocent person
     
    Last edited: Feb 25, 2012

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