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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. bobscogin
    Joined: Feb 8, 2007
    Posts: 1,761

    bobscogin
    Member

    That's the whole point here. There shouldn't be any oscillation in a properly designed and set up steering system.

    Bob
     
  2. seb fontana
    Joined: Sep 1, 2005
    Posts: 6,924

    seb fontana
    Member
    from ct

    You can move the arm in till hits the body or make clearence for it..That is a Crosley box and I'll bet that the bracket bracket is flexing when the sector shaft flexes and I wonder how the shaft was made longer as in your first post you already broke the steering shaft? How did you get the support bearing on?..
     
  3. pitman
    Joined: May 14, 2006
    Posts: 5,041

    pitman

    I still would like to know how close to bring in the pitman arm to the body? The drag link might run straight ahead if the sector shaft was shortened as much as you can, and still clear the body. Moving the outer brn mount helps, (or shorten the shaft!) as the torsion loads remain, you will have greatly lowered the addit. bending loads on the shaft.

    and

    The proper name of the triangle that the dead link attaches to? The mount on the axle? It is usually part of the hairpin mount plate.
     
    Last edited: May 27, 2013
  4. blue 49
    Joined: Dec 24, 2006
    Posts: 1,365

    blue 49
    Member
    from Iowa

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

    All American 6
    Member
    from Sumter, SC

    Some have asked what type of steering box is it.

    SPE worm type - Strange Engineering sells them.
     

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  6. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    First mention I have seen of torsional loads on that loooong sector shaft. I don't think bending is the issue there so much as torsion.

    Regardless, this is probably not the cause of the problem but sure won't be helping to control it.
     
  7. pitman
    Joined: May 14, 2006
    Posts: 5,041

    pitman

    Cause of the wobble: If you look carefully at the left front of car pic, the king pin inclination (and it's centerline) will not place the contact patch under the tire, the wheel is offset to the outside. Then there is the "trail" input-force from positive caster angle with each direction change of the rim.
    Now place a very large, cast-iron bowling ball, right in the center of the engine block...that is the Mass. The entire front suspension will oscillate, (Okay, wobble) when a bump, ridge, or force contacts either front tire.

    Consider it a "steering input". Except it is from the wrong end of the system. The entire front susp. & steering-gear linkage is swerving side to side, as it corrects, to keep the Mass, above it's centerpoint. Each element, say the front tie-rod, has a spring-like behavior, as does a longer sector shaft.

    The mass behaves like an inverted pendulum in a case like this. A damper might slow it, but correct geometry should prevent the wobble in the first place.
     
    Last edited: May 27, 2013
  8. KK500
    Joined: Dec 29, 2006
    Posts: 354

    KK500
    Member

    OMG........how many times do u have to be told that the steering box, shaft and bearing are TOTALLY inadequate?
    Read the Strange Eng website again.......Thos steering boxes are made for dragsters, you know, those cars with spindle mount front wheels cos there's no weight over the front wheels......they don't hit bumps, and don't supposed to steer.

    Replace yours or park it and polish the billet!

    Jim
     
  9. H.G. Wells
    Joined: Mar 11, 2006
    Posts: 386

    H.G. Wells
    Member

    That SPE box is made for a dragster. And as said earlier is entirely insufficient for a car. This may or may not actually be the cause of your trouble, but does need to be change.
     
  10. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member

    Forget all the comments about the steering box being insufficient . Compare a Funny Car at 200mph with a Road Queen at 60mph.
    The problem is with basic engineering faults in numerous areas [ all escalating together ]

    Death Wobble starts at the Tyre footprint not from where the Hands hold the steering wheel

    Get somebody to sit in the car and stand on the brakes [ really hard ], and move the steering back and forth
    If you do this you should see the flexing in the drag link or sector shaft

    I see this problem time and time again, never on an original car but always when somebody re-invents the wheel to “make it better”
    If you remove poor mechanical condition [ worn parts ] out of the equation , most of the time the problem is cause by smaller diameter wheels and improper wheel offset.

    Original Fords for example had skinny wheels which were quite tall

    Too much scrub radius causes drag on the wheels which creates tension on the tie rods.[in this case ]
    Too much positive caster creates compression on the tie rods.[in this case ]

    This would be OK on a dead flat surface, but I have NEVER seen that in my life.

    You need to start again on the front axle ,Luckily the front end is completely unbolt able.
    In fact it could be quite cheap to remedy [ There is always some swap-meet fool that will buy a complete “shiny front end” ]

    I would recommend starting with spindles that have the king pin inclination closer to the centre of the tyre footprint . This will cause less drag so the steering arms can also be shorter and fit inside the wheel.

    If you have trouble grasping all this, talk to some “sprint car” people.
    They have beam axle setups down to an art and are used in atrocious conditions [and carrying the left front etc without wobbles ]
     
  11. 32John
    Joined: Dec 2, 2012
    Posts: 21

    32John
    Member
    from Sydney Oz

    I can't see a panhard bar on your front end, but it looks like it has shackles on both sides of the spring. I had that setup on my A coupe when I bought it, and I experienced a couple of fearful death wobbles at speed- mine was even more sensitive to the lack of a panhard bar than your front end is because mine was setup cross-steer. Your front end can just swing sideways on those shackles and the mono leaf probably makes that tendency worse.

    I installed a panhard bar and I've never had even a hint of the wobbles since.

    I'd also echo the comments earlier about the front wheel offset- that makes it a lot more sensitive to hits from bumps. And also echo the clevis ends on the batwing attachments of the 4 bars- those aren't meant to provide for any rotation of the bars. And the shock is so far from the wheel that it would have trouble controlling it...
     
  12. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

    This is all (mostly all) great info and we're putting it to use this morning.

    More to follow on our success, partial success or failure.

    Appreciate it much,
    AA6
     
  13. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I don't care what anyone says, if you take that small of a steering box, hang a very long output shaft on it, then sit a heavy hemi on top of that setup, it is going to flex. The reason steering boxes that are designed for street use have a "high spot" built into them is to add some resistance to the steering system to counteract back and forth movements being exerted by the tires. I bet that dragster steering box has no high spot as it was built to go down a relatively smooth strip a quarter mile at a time.

    The real issue here is, this car was built to do one thing and now it is being asked to do a completely different job. To successfully do that it is going to take some serious revamping IMO.

    Don
     
  14. bgaro
    Joined: Sep 3, 2010
    Posts: 1,189

    bgaro
    Member

    interested to see what you come up with, i'll be watching. this kinda thread is what makes the hamb so good.
     
  15. The point people are trying to help you with, is that you already broke parts and got lucky. All the comments are directed toward you being safe.

    Keep that light weight dragster box on -that- car with that setup, and ask it to do more than it was ever designed to do, and next time you might not be so lucky.
     
  16. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

  17. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,792

    tfeverfred
    Member

    Definitely NOT the one for a funny car. It's not meant for a street car. You'll be back where you are now.
     
  18. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    Didnt you say the mount for the input shaft for the box was cracked, ie weld gave loose? Host of many maybe.
     
  19. Pete Eastwood
    Joined: Jul 27, 2011
    Posts: 1,004

    Pete Eastwood
    Member
    from california

    I've read this whole thread. There are lots of problems with this set up.
    Tell me you DON'T drive this on the street. If you do drive it on the street . . . park it.
    As others have said that steering box is ok for dragsters, and it's just barely adequate for funny cars.
    The spindles look like they are Chevy type. That adds to the problem, the king pin inclination is less than on Fords & the PS style that drag cars use.
    If this car is going to be driven on the street, you've got some changing to do.
     
  20. It's not hard......go to your local pic-a-part and get a box off a street car.
     
  21. Fixes the problem but doesn't cure the problem? I'm stickin' a damper on mine.
     
  22. A Rodder
    Joined: Jul 13, 2008
    Posts: 2,477

    A Rodder
    Member

    Good read in any case.

    Good luck with the fix. There seems to be a lot of good responses on this thread from informed people. That is what is great about this forum.
     
  23. bgaro
    Joined: Sep 3, 2010
    Posts: 1,189

    bgaro
    Member

    schroeder, that'll handle the job.
     
  24. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

  25. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,792

    tfeverfred
    Member

    Doesn't sound like I expected it would. Those wheelie bars wouldn't last long around here.
     
  26. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

    Panhard bar has been fabed and installed.

    Steering box came in finally. The box mount will be more solid.

    Testing to follow.
     

    Attached Files:

  27. Pete Eastwood
    Joined: Jul 27, 2011
    Posts: 1,004

    Pete Eastwood
    Member
    from california

    So tell me the difference between the SPE box you had & the new Stilleto box.
    Aren't they the same, light duty dragster type box, not designed for street driven cars ?
    Open them up, I'll bet they look the same inside.
     
  28. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

    I never felt the SPE box was an inappropriate design for my application. It just wasn't mounted solid enough for street use. Once we took the box off, we found some play and worn spot on the worm gear.

    The panhard bar took 99% of the wobble out. I think experimenting with toe in at 0 will do the rest.

    Adding a universal joint on the steering shaft.

    Hopefully, a damper will not be necessary (mostly for aesthetic reasons).

    Here are some pics of the car earlier in the month driving into the Hot Rod Power Tour Birmingham stop and at a cruise in last weekend.
     

    Attached Files:

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

    All American 6
    Member
    from Sumter, SC

    * New steering box installed. Good solid mount. The gears in the box are much finer than what I had. Stronger internal design too.

    * Shorter pitman arm shaft. (Had to be shortened - Stiletto couldn't make a custom size timely)

    * Larger / stronger support bearing for the pitman arm shaft. Stiletto advised against using more than one - too hard to get it all on one plane.

    * New steering column with brass bushings. New solid steering shaft with added universal joint. That universal joint also makes it where the system doesn't need to be perfectly square.

    * toe out is now + 1/16" Once the rain stops, we'll see how that works.


    (previous posts included heavier drag link & tie rod; install panhard bar)


    Besides playing with the alignment this should have it. (it was close with just the panhard bar added)



    First three pictures below are with wheels turned right all the way. The new set up will give me a tighter turn radius.
     

    Attached Files:

    Last edited: Jul 5, 2013
  30. All American 6
    Joined: Sep 25, 2012
    Posts: 234

    All American 6
    Member
    from Sumter, SC

    On a different note: I'm looking for a metal deck lid for the 34 Plymouth. Any leads? reproduction is fine.

    Also, know of any good vendors for a grill insert?

    Thanks,
    AA6
     
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