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Technical Violent steering wobble at low speed

Discussion in 'Traditional Hot Rods' started by 1963Gasser, Feb 20, 2017.

  1. F&J
    Joined: Apr 5, 2007
    Posts: 12,149

    F&J
    ALLIANCE MEMBER

    I did look at the pics you did put up, but one pic that should be taken is:

    --Get right in front of one inner front wheel, camera looking straight at the relationship of the king pin, and the imaginary line of that king pin should point to a spot UNDER the front tire at road surface...not pointing to the ground alongside the inside of that tire. The term for this is called Scrub Radius.

    Try to explain here... Lets say your imaginary line of the pin center comes down to the pavement 2"-3" away from the tire sidewall... Now hit a pothole or bump with that tire way out there, that gets more leverage thrust into the steering linkages, box, etc.

    Now think of how much less leverage a bump or pothole would have if that imaginary line ran right down under the center of the tire where it touches the road.. No leverage at all.

    Adding discs to a car like a Hamb-typical old Ford beam axle hotrod, does shove the tire out.... mainly due to the rotor design and where the caliper needs to clear other parts. .... Also, if there is not enough backspace on the wheel, then it shoves the center of that tire out even further.

    No one thing causes Wobble..that is why each wobble car might have a totally different problem or multiple things.

    The damper may be what you will end up with if you cannot fix an improper scrub radius, or don't want to change a bunch of parts,.................. and depending on how far off the scrub really is, and if the total weights of tires/wheels are causing even more of the issue, ...then you may even need a stronger damper like VW bus or even bigger.. Time will tell, but the VW bug one should "stop, or prevent", the "Start"of the wobble "event".
     
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  2. christmas tree
    Joined: Dec 7, 2009
    Posts: 321

    christmas tree
    Member

    Here,s my ride and here, s my story Ran near 100 in quarter and low 80,s in the eight and put away for the winter. Next spring prepping I had a low front tire so I aired them up plus a few extra lbs. for less rolling resistance which I thought made sense. Went to the local strip and ran 83-84 and slowing down to 70, I,m guessing had violent wobble. Loaded up and went home. What went wrong???? Started checking and the 1/8 in tow in was a measured 1/2 in. Lesson learned read the measure yourself. With the low tire pressure (25lbs) and too much tow in it handled good but with extra pressure and too much tow it was evil as hell.Backed up and 32 lbs tire pressure and 1/16 to 1/8 tow in goes straight as an arrow and no wobble at any speed.6 deg caster 16804677_1710180322341677_966733510_o.jpg speed.
     
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  3. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA

    had tow in set at 1/8 now moved it to 1/4 still no change in wobble
     
  4. jimvette59
    Joined: Apr 28, 2008
    Posts: 656

    jimvette59
    Member

    I developed a shimmy on my 34 ford after about five thousand miles. To make a long story short I rebuilt the front VW calipers and it was back to normal. The angle of inclination should be the king pin angle to the center of the tire. Maybe those reversed wheels do not work on this front end. Please study Ackerman JMO
     
    Atwater Mike likes this.
  5. Get the alignment set by a professional.
     
  6. Boneyard51
    Joined: Dec 10, 2017
    Posts: 845

    Boneyard51
    Member

    Having the alignment set properly sometimes will not solve the problem. Sometimes you have to change something to eliminate a problem. Lots of times , here in the US shops are not willing to change things, due to liability. I had three identical new trucks in my fleet, build in consecutive order on the assembly line. One developed a tendency to wobble after hitting a chuck hole, the other two never did. Had alignment checked, perfect, same as the others. Checked wheel balance, perfect. No worn parts( new truck). Installed 2 degree shims under the axle, never had another problem. Bones
     
  7. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA

    Though I had it licked today , found the pitman arm wasn't going far enough up the splines. Nut was bottoming out before arm was tight, made a washer with clearance so I could tighten the heck out of it. Double checked the steering box to make sure sector gear is centered up. Found out that the pitman arm (speedway motors 2 inch drop) had a .645 dia hole in the small end , I had been using a 5/8 .625 grade 8 bolt . I welded up and turned shoulder down to .646 or so and pressed it in.
    then I took her out for a test drive. It steered great for the first few miles, bumps in the road had no effect on car. Until I went across the seam in a bridge by my house and sure as hell the wobble started again, until I slammed on the brakes to get rid of it. I have ordered a steering damper that will be my next try.
     
  8. NashRodMan
    Joined: Jul 8, 2004
    Posts: 1,423

    NashRodMan
    Member

    I had the same issue on a previous car and tried the steering damper. It did not help. I've read many times that the aftermarket vega boxes AND the Flaming River boxes are crappy. You might want to consider going with the Borgeson box. JMO from personal experience. Good luck.
     
  9. EVERYTHING from Speedway is suspect.

    Start there.
    Take it apart.
    Check everything.
     
    Last edited: May 16, 2018
    nochop likes this.
  10. Don't fucking tell me, you welded the bolt ?
    Any idea what that does to the heat treating on the bolt ?
     
    ottoman likes this.
  11. alchemy
    Joined: Sep 27, 2002
    Posts: 12,170

    alchemy
    ALLIANCE MEMBER

    You still didn't tell us what the scrub radius looks like. Show us a good straight-on photo from the front so we can see if you have too much offset on your front wheels. Show the spindles, and wheels touching the ground, from straight in front.

    Also, have you ever checked your Ackerman angle? I think those steering arms look rather straight-back, but maybe the photo angle is deceiving. This might not effect the death wobble, but sure will make turning a corner easier.
     
    F&J likes this.
  12. F&J
    Joined: Apr 5, 2007
    Posts: 12,149

    F&J
    ALLIANCE MEMBER

    Agree 100%. If this is way off, you are pissing in the wind, so to speak.

    I think I said already that if the tire contact spot is far away from that imaginary centerline of the king pin, you sure as shit will have that tire try to steer. The further off it is, the more violent that tire gets steered. Ok, so you hit a bump/hole with the passenger tire, that tire will HAVE to steer to the left. Then the tie rod shoves hard against the opposite side steering arm/spindle/wheel. If you run heavy caster like 8, that opposite tire wants to stay straight...and if a cheap thin tie rod is used that flexes on compression, you are aggravating the "chain reaction" which is Death Wobble. The two tires are now playing "catch up", not really synchronized!

    One Hamber that runs a vintage pro salt roadster said he ran the old build as is, with very excessive caster, and cured his by running a massive tie rod. Another hamber with a fenderless street car, jacked the front up and was strong enough to grab the front of each tire at the same time, and pull/push each way, and his cheapie tie-rod flexed a lot on compression.

    Towards the final years of Dick Spadaro's posts on wobble on old Ford beam axles, he then advised running less caster than the old wives tale of 7-8.

    Ackerman can be checked by wheel alignment equipment. The spec on that is called "toe out at turns". Most people likely have never though about the fact that when you are dead straight, yes, you have toe in,...but as you start to turn, the toe in, then becomes "toe out" to be able to get the Ackerman effect! Now throw that toe-in setting that you have, into the mix when working on a wobble car...this is why some have lucked out by making a simple toe change in certain wobble cars.

    .
    Like was said, wobble is not just one problem, never exactly the same cause on each car that wobbles. One thing to keep in mind is that wobble really is a "chain reaction". Once you get that in your head, then you start realizing what happens to the opposite side when one wheel hits something. This is why many have used a damper to "stop" the first beginning of a wobble event.


    .
     
  13. Correct.
     
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  14. Tetanus
    Joined: May 20, 2007
    Posts: 186

    Tetanus
    Member

    I was thinking the same thing.......WTF
     
    ottoman and Unkl Ian like this.
  15. How are you measuring this "rake" ?

    Is that the same as what is properly called Caster ?
     
  16. Stan Back
    Joined: Mar 9, 2007
    Posts: 339

    Stan Back
    Member
    from California

    Well – Here's the long story how I learned so little about scrub radius. I are not an alignment specialist, but I know when something does not seem right.

    I have a Bonneville Street Roadster. It used to be competitive, but time runs on. Ten (or more) years ago, I was gifted a set of four Centerline wheels. Looked great. About that time I was changing to 4-1/2 inch wide 22-inch M&Hs on the front. I'd been running 25-inch (and wider) M&Hs on the front on steel wheels and had run 199 with about 7º of caster. Hoping for 200, I thought I'd try the M&Hs. Narrower, shorter. I put them on the really nice Centerlines. Looked great! I rolled it out of the garage, then pushed it forward to a hunk of 2x4 to stop it. What the fuck?!?. The steering dashed left. What's that all about? How would that be at 200 MPH if I hit a clump or rock? I was told that the angle projected thru the king pin would be best to intersect the middle of the tire.

    Looking at that made sense. I had some steel wheels made up that had the most offset they could give me. They intersected the tire, but not at the center. Next time I ran, I found out that I could actually STEER the car! And went 201 and got in the two-Club with a change of wheels and tires.

    A well-known-and-financed team with another Street Roadster spun about every 2nd run, including trying to best my years-old record at El Mirage. I was talking to their top component manufacturing owner about this at Bonneville years ago when they were servicing the car in Impound. I remarked with their sorta "white trailer wheels" how hard it must be to keep it on tract at speed. With their offset, they were nowhere near the tire patch. I tried to tell them what I'd learned. No response. They spun.

    You can do this with a ruler. Project the king pin inclination. If you're inside the tire, you're in trouble.
     
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  17. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA














    (Also, if there is not enough backspace on the wheel, then it shoves the center of that tire out even further.)

    Very good point Sir. I had the rims made with a small back space so that the car front end did not look to narrow.
    Yesterday I was experimenting with different toe in and air pressures.
    Sounds funny but with 1/16 toe in (witch is really hard to check accurately ). and 25 p.s.i. in front runners , I could not get it to wobble at any speed or any size pot hole.

    Today the vw damper came in and I fabbed some brackets and mounted it. It cant be seen from front of car.
    Then I went out hunting bumps and pot holes with 1/8 toe in and 32 p.s.i. Well you people that live in commyforma know I didn't have to look to hard or to far. Ran though 1/2 a tank of gas and every bump from here to hell and back, no wobble. So I am 90% sure I got it licked . We will see , thank all you guys for the help. Now I am going to check in to why my new munice m23 keeps locking up when going from 2nd to 3rd. lol
     

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  18. Atwater Mike
    Joined: May 31, 2002
    Posts: 8,284

    Atwater Mike
    Member

    TIRE BALANCE!!! By a competent 'tech' on a modern machine. Dynamic balance will tend to gyroscopically turn the inertia of a spinning wheel (tire) 'in', or 'out'; when it gets to the end of its free play (any slop in steering linkage) it recoils, then again, then again. Quickly. Nearly pulls the wheel out of your hands.
    Sells lots of dampeners...before the problem is ever identified...then corrected...
     
  19. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA

    ok I will take some pics today . there are so many vehicles on the road today that have the wrong ackerman steering radius set up. hell even my 4 door chevy dullie scrubs the tires hard.
     
  20. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA


    I will check today
     
  21. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA

    I will fab a new bolt today.
     
  22. Eric GILROY
    Joined: Apr 22, 2017
    Posts: 39

    Eric GILROY
    Member
    from GILROY CA

    ok good news the ackerman steering radius is dam near perfect. The bad news is center of king pin angle hits about a 1 .25 from inside sidewall of tire. and on the welded bolt I am thinking of boring and sleeving the small end of the pitman and using a new grade 8 bolt . I might get some 2 1/2 inch back space rims to move tire in another 1/2 inch. Rim is getting close to caliper see picture measuring tape is .700 thick. My race car is loaded in trailer for tomorrow but I have a picture of front axle and its kingpins don't even come close to being pointed at center of tire but car goes straight easy.


    Sorry to have stole this guys thread but I forgot how the start a new one , but (invisible kid ) called me to help out. Pictures are not in any kind of order lol
     

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  23. alchemy
    Joined: Sep 27, 2002
    Posts: 12,170

    alchemy
    ALLIANCE MEMBER

    Oof! The offset on your car (and that T) is really bad. Can't be good for anything. I'm no alignment genius, but I would guess that is part of your problem.

    Don't let the brake calipers be your excuse for not getting the proper offset wheels. Those calipers came off of some car, and I bet it rolled off the assembly line with the proper offset. If you want to eliminate your death wobble problem, find a proper offset pair of wheels and give them a try.
     
    Unkl Ian likes this.
  24. jimvette59
    Joined: Apr 28, 2008
    Posts: 656

    jimvette59
    Member

    What I said. Go back to basics. KISS. JMHO.
     
    Unkl Ian likes this.
  25. manyolcars
    Joined: Mar 30, 2001
    Posts: 7,338

    manyolcars

    Check the length of wheelbase on each side of the car. One side longer than the other can cause death wobble
     
  26. Engine man
    Joined: Jan 30, 2011
    Posts: 3,409

    Engine man
    Member
    from Wisconsin

    Seems that you found the settings that your setup likes.
     

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