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Death Wobble

Discussion in 'The Hokey Ass Message Board' started by All American 6, May 25, 2013.

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  1. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

    Yep, another death wobble thread. I searched and read the larger threads. There are 22 (23 now!) threads with death wobble in the subject.

    Strengthened the mount to the shaft coming out of the steering box. Replaced drag link and tie rod. Added gusset to the triangluar piece at the drag link bolts to at the wheel (would like to know the proper name of that piece).

    Replaced the front tires too.

    I really thought I had it whuped.

    We'll play with the toe, caster and camber more. Tudor's thread from 2009 had 305 replies - some of which were useful.

    I'm just venting,
    AA6
     

    Attached Files:

    Last edited: Jul 24, 2013
  2. Plently of tow in and fit a steering dampner.
     
  3. A steering damper is just a cover up..Whats your caster?
     
  4. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,254

    Hackerbilt
    Member

    You broke the mount and also the steering shaft.
    Looking at the distance from the tierod end of the pitman arm to the outer support bearing I see lots of potential for flex between the pitman arm and the bearing which would likely result in equal flex between the bearing and box.
    Result...a broken mount and a broken steering shaft.

    MY cure would be to redesign the steering box extension shaft to have a solid bearing directly inboard of the pitman arm and also make an additional mount that solidly secures that round output bearing housing on the steering box itself to the chassis.
    Better yet, an extension tube that press fits the output bearing part of the box, going from the box to the frame (enclosing the extension shaft itself) and beyond with an inner support bearing at the pitman arm and additional mounting to the frame to support the box itself would be perfect.
    Whatever you come up with, overbuild...don't go for pretty and light.

    ...or you could get a sprint car style box that spans the distance and takes care of everything itself.
     
    Last edited: May 25, 2013

  5. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Not sure where to begin. One thing that jumps out at me is the engineering of the steering box itself. It looks rather spindly and more suitable to a lightweight dragster than a heavy street driven hot rod. Not dissing your work, but the gussets are very thin and that steering shaft is the longest I have ever seen, especially the portion that sticks out past the support. There is just so much room for flex in that whole shaft assembly that I can only imagine how much it can move under road conditions.

    I don't know, the whole steering setup just seems a little unorthodox to me for a street driven car. With this setup as it is I am not sure if you will ever completely solve your steering/handling issues.

    Don

    [​IMG]
     
  6. fab32
    Joined: May 14, 2002
    Posts: 13,985

    fab32
    Member Emeritus

    Must be why So-Cal puts one on EVERY car they build. And in talking with Pete Chapouris the answer is not just because they sell them. Besides dampening the oscolations of the steering system it also makes for a smoother feeling system through out the full range from lock to lock.

    Frank
     
  7. titus
    Joined: Dec 6, 2003
    Posts: 5,145

    titus
    Member

    I think they definately help but i feel there are other underlying problems also, ive put together a few cars and never have used a dampner. early on i had a problem with a car but re-adjusted the caster and was fine. I think socal puts em on for the "cover all bases" idea.

    JEFF
     
  8. Fenders
    Joined: Sep 8, 2007
    Posts: 3,921

    Fenders
    Member

    Are you sure what you have is death wobble? Driving down a smooth road at any speed is fine, but DW is a shake in the front wheels transmitted to the steering, initiated by going over a bump or piece of bad road at low speed.

    You can often drive your way out of it by speeding up.

    I had DW when I first got my rod on the road -- the cause was incorrect toe. (I actually had toe out, fixed it to 1/8: toe in and all was fine thereafter).
     
  9. A death wobble is not normal osculation of a steering system and to try to correct that type of a condition without addressing the root cause is not the proper way to solve the problem . Some of the things you want to check are...
    1. Geometry changes;
    a. incorrect ackerman (the line from the center line of the king pins, across the centers of the tie rod ends, to the center of the rear axle; often caused by changes to wheel base.

    b. incorrect camber; (the center line of the king pin to the contact patch of the tire ) Changes in wheel/tire diam. is one cause. The next is sever "offset" wheels. (moves the tire contact outside the king pin center line, and probably the biggest cause of wobble, especially with bias tires. (on small changes to steering direction the tire tries to "seek" the contact point)

    c. Improper castor (usually not enough)

    2. Loose (worn) parts. Can run the gamit from worn king pins/bushings. Worn tie rod ends. Worn steering box. Loose wheel lug nuts; there's more. (if you can grab a front tire, with someone holding the steering wheel steady, and get side to side movement SOMETHING is worn or lose!)

    3. Poor front end alignment. Toe-in and toe-out not set properly. (if the rear axle isn't located properly, IT can cause problems too)

    4. Poor quality tires. Out of round or have "side set"; means the tread does run not true. Cheap bias tires are bad for this problem. Yeah bias tires are "neat", but radials are safer!

    5. Out of balance tire/wheel combinations.
     
  10. Weasel
    Joined: Dec 30, 2007
    Posts: 6,698

    Weasel
    Member

    I'll add wheels with runout - either lateral or horizontal and brake drums (although not in this case) out of round or unbalanced to the list posted by themoose....
     
  11. pitman
    Joined: May 14, 2006
    Posts: 5,148

    pitman

    I'z an injuneer, Hacker and Don raise some real concerns!
    The loads on the outboard end of the shaft look scary! Not likely to hold up.
     
  12. bgaro
    Joined: Sep 3, 2010
    Posts: 1,189

    bgaro
    Member

    yeah, just throw a chinese so-cal dampener on there and your good. hahhaha. gusset the heck outta that shaft and check into caster.
     
  13. 1971BB427
    Joined: Mar 6, 2010
    Posts: 8,719

    1971BB427
    Member
    from Oregon

    Another thing that can cause death wobble is flexing of any steering component. If the tierod, draglink, or any piece is too lightweight and can flex, it will change geometry and allow the frontend to flex and wobble. Check the wall thickness on all these parts, and replace them if needed. Larger diameter or thicker wall will stiffen them up, and reduce flex.
     
  14. brad chevy
    Joined: Nov 22, 2009
    Posts: 2,627

    brad chevy
    Member

    I agree with Don on this one,the way the bearing is mounted you are lucky you haven't wrecked yet. That is where all the stress is and a dampener will just put more stress on it. All it would take is one pothole and it will break again. Better bearing and much stiffer mounting bracket would definitely help.
     
  15. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,791

    tfeverfred
    Member Emeritus

    [​IMG]

    THIS is something that has to be addressed. I'm no engineer, but I know enough that I wouldn't run this on a soap box derby car.
     
  16. trollst
    Joined: Jan 27, 2012
    Posts: 2,108

    trollst
    Member

    I notice you have to have a serious case of bump steer, your four bar mounts being way ahead of the drag link, surprised nobody else saw this. Your death wobble and breakage come after hitting something with the left front tire, (pothole, manhole cover, crack in the road, etc.) causing the steering to try to turn when it can't.
    Nothing will change this, you need to lengthen the four bars, all the hinge points HAVE to be the same to avoid bump steer, reengineer your steering setup before you kill yourself or someone else. This stuff ain't about bolting parts together and hoping for the best.
     
  17. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Hope you don't take this as busting your chops, but that entire front end needs reevaluated and redone. The steering is never going to be right as it is designed, and the shocks also are not contributing much to the dampening effort. I know it is always tough to redo a car once things are all painted and pretty, but I think you will be chasing problems of one sort or another forever if you don't redesign it.

    As for the So Cal stabilizers, here is my take on them. They are not designed to cure a bad problem, they are designed to take a good handling car and make it a VERY good handling car. We have them on 3 cars (soon to be a 4th car) and will never build another one without one. I like to drive my cars like a car should be driven and the stabilizer gives me a lot of peace of mind that I can do just that.

    Don
     
  18. pitman
    Joined: May 14, 2006
    Posts: 5,148

    pitman

  19. fit a steering dampner. fit a steering dampner.
    You can dance on the moon even but you need a steering damper. There may be absolutley nothing wrong with your steering . Sometimes when we hit a bump the wheel takes a wobble . Like a small gyro it wants to remain in that plane wierd as it seems. A steering damper says NOPE!
    Usaully this shows up at relatively low speed. Sometimes during the burn out and sometimes on the return road of the track is bumpy usually the car is very stable at high speed. Anyway I have been down that road enuf times to know . just take an hour and install a steering damper and be done with it.
    With the old style steering it is impossible to get perfect geometry. The long link from the steering box hooked to the pitman arm and running to the steeing arm will never have the same arc as the front axle and everytime the frame in relation to the front axle the car wants to some extent steer. That would be ok except without a damper it wants to repeat that motion. The damper ends it. I was running my little rail at the left at Shannonville for several years. It is quite smooth and I never had an issue. The last couple for years I have switched to airfield racing (which is unbelievable fun without the hassles) These airfield are they way they were during WWII and have never been resurfaced. There can be some nasty bounces here and there which can cause the problem you speak of. Last year I arrived home , went to town, bought a VW bug steering damper and installed it in about a hour. Problem is completely gone , not even a smidgen of a sign of it. I had been down that road before so I knew what to do. It begs the question if you think there is a design flaw only that causes it why does the VW Beetle have one. Why do most 4WD trucks have they just to name a few examples. The folks who advised you to install one are giving you sound advice.
    Don
     
    Last edited: May 25, 2013
  20. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    We are concentrating on one picture, but is that the problem? Not sure. Maybe the flex is happening there. Could be..

    Bad angles, wrong toe, slop in the system. Maybe its suspect but there are a lot of stuff going on here. My guess, and it is a guess is too much loosey-goosey somewhere. Check you toe and check your slop. More componets in the system effects the end result.
     
  21. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    doh! Sometimes I should shut my trap. ha ha. I do have my moments though...
     
    Last edited: May 26, 2013
  22. terrymetal
    Joined: Apr 23, 2013
    Posts: 10

    terrymetal
    Member

    I see a lot of good answers here but one thing is certain....I imagine it is hell to drive at all and best advice I can come up with is DO NOT DRIVE until the steering and suspension is 100 percent. I see too many things that can go wrong with the simplicity of some of these cars fronts ends compared to newer cars. There is no single solution to this problem but if it was my car I would call a steering expert and ask what can be done....It sucks to start over but in the end its the best thing you can do in this situation.....Just trying to help. Terry
     
  23. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,791

    tfeverfred
    Member Emeritus

    Nope. There are thousands of cars with that setup. The engineering needs to be redone. Plain and simple. Anything else is a quick fix and could prove hazardous.
     
  24. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,906

    Kerrynzl
    Member

    If I am seeing things correctly in these 2 pictures, it appears that the King-pin inclination is wider at the top than at the bottom.
    [ It almost looks like the spindles and axle ends are upside-down ]
    Could you take more photos to confirm this.

    If my observations are correct you have excessive scrub radius.
    Excessive scrub radius causes a chain reaction when it hits a bump [ the poor old pitman arm hanging out on that cantilever mount is the weakest link ]

    Instead of patch-up remedies [ steering dampers etc ] try and get all the basics correct.
    You might need a new axle

    The King pin inclination should intersect at the centre of the tyre footprint ,so there is equal drag on each side of this point.
    If you have correct king pin inclination and zero caster the tyre will “fall over” when you turn the steering either direction [ positive camber ]

    Positive caster is used to counteract the positive camber on the outside tyre [ less steering angle requires less + caster ]
    Note I am referring to steering angle at road speeds , the excessive steering lock in supermarket car parks is not detrimental to handling [ unless you autocross ]




    [​IMG]

    [​IMG]
     
    Last edited: May 25, 2013
  25. stev8
    Joined: Jun 22, 2007
    Posts: 87

    stev8
    Member

    I dont think that Clevise joints on the front of the four bars is the wisest either. (If it has conventional four bars there, a little hard to tell from photo!).
    Clevise joints arent really designed for movement, really designed for simply holding something in place. Rod ends would be better.

    Also, larger washers on the bolts holding your rod ends in place would be safer too. If the rod end collapsed or broke, at least a large washer would stop it all coming apart complety, at least till you got to the curb and stopped...especially on the steering!!!
     
  26. terrymetal
    Joined: Apr 23, 2013
    Posts: 10

    terrymetal
    Member

    Not a bad idea to use safety wire on some suspension parts also....I completely agree Stev8
     
  27. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member

    Good eye to catch that view of the KPI. I suppose it could be camera effects, but it sure does look really bad.

    And yes, scrub can trigger low speed D.W. I experienced that over 40 years ago when I put wrong offset mags on a 50s built rod. I have been reading about wobble ever since. Note I said "trigger", not "cause". I still think there are many different combinations that "cause" it, and it seems adding just one more iffy thing, can trigger it.
     
  28. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    What is the steering box from? Looks like a Crosley [ross] which is not a preloaded no play type box, also not very strong..Any play in the pitman shaft bearings and no matter how much load at center you adjust in there will always be play at the pitman arm..Front is a four bar so clevises should not be used..I too think to much wheel offset but the king pins do look pretty vertical too...BUT at least the steering arms show there was ackerman considered..
     
  29. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Stev8 is right, clevis ends are made to not swivel like rod ends. The holes will wallow out real fast as the axle moves up and down. You need to get spherical rod ends on there in place of those clevises.

    Don
     
  30. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    Usually I can spot something on a front end that is the main cause of a problem but that particular front end setup has so many questionable things on it that I am having a hard time sorting it out.

    The obvious steering box setup, the 4 bar being a bit short in comparison to the drag link, the angle of the shocks and mounting of the shocks, and the wheel offset to clear the splayed out steering arms are things where each could cause a bit of an issue on their own. What appear to be a long steering arm off the spindle as compared to the pitman arm might be an issue along with causing a very large turning radius.

    Are the wheels balanced correctly? Has the car been on an alignment rack to actually check the alignment or was it just done with stick and string? Have you checked each and every rod end to make sure that there is no slack in either the rod end or the bolt holding it?
     
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