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Technical *UPDATED* Death Wobble Search and Destroy Mission

Discussion in 'Traditional Hot Rods' started by Shawn Wildman, Sep 12, 2020.

  1. Shawn Wildman
    Joined: Jul 8, 2018
    Posts: 23

    Shawn Wildman

    I picked up a 1941 Ford 1/2 ton pickup as a project. I've noticed a REALLY bad shake at 45-55 mph ONLY. All other speeds the truck is fine. After some research here in the Forum I started checking out the minor stuff on the truck. So far I've checked:

    1. Drive line angle. With a custom set of parallel rear leaf springs, 4" drop in the rear and an aftermarket transmission mount for an S10 T5 mounted to an 8-BA in a 1941 pickup, one of my first suspicions was the drive line angle was out. It turns out it's pretty good. The Operating angles of the transmission and differential are within 0.4 degrees. Only concern was the transmission, driveshaft and differential are right in line with each other. After some research it looks like this is acceptable.
    2. Front tire runout, side to side and radially. Both look fine.
    3. Loose nuts in the suspension. All fine.
    4. Worn front bearings. Both are fine.
    Then I checked for loose steering components. All of the steering components are fine, but when I moved the left front tire side to side I can feel a wobble, however I can't feel the same wobble in the right front tire. So, I had my daughter move the left front tire while I climbed under the truck. This is what I found (sorry for the flickering light, LED lights don't work well with video cameras):

    https://drive.google.com/file/d/1z2U11bvpAa1YuL3jUmHvOrYko7qctrcs/view?usp=sharing

    None of the steering components were moving when she was shaking the tire. Only the spindle moved relative to the front axle. I'm new to solid axle front suspensions, so I'm guessing a worn out king pin hole in the axle? I think the guy who restored the truck used the original front axle and suspension components. I imagine this is something I should fix, but is this bad enough to cause a shake in the truck to the point where you WOULDN'T want to drive it at that speed?

    Here are pics of the rest of the suspension:

    20200912_123826.jpg
    20200912_123840.jpg
    20200912_123850.jpg

    The reading I've done on the forum about eliminating death wobble is mostly about alignment and steering dampers. Which raises a question. What should the alignment specs be for this setup (dropped 4" in the front, I think) be? I plan to check the balance on the tires, which have been dynamically balanced on both sides, but figured I would have the alignment checked when I take it to the shop.

    Any recommendations are welcome. I can drive the truck, I just don't drive between 45-55 mph.

    Thanks!
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 46,909

    squirrel
    Member

    Death wobble means the steering wheel is turning back and forth quickly, all by itself. Is that what you experience?

    The video shows a loose kingpin/bushing at the bottom, I think.

    Driveshaft issues cause a rumble, not a shake. It's at roughly 3 times wheel speed.

    Most axle setups want 5-7 degrees caster, perhaps a degree of positive camber, and around 1/16 or so toe in.
     
    ClarkH, pitman and jimgoetz like this.
  3. Shawn Wildman
    Joined: Jul 8, 2018
    Posts: 23

    Shawn Wildman

    What I'm experiencing is a shake in the whole truck, not just the steering wheel.
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 46,909

    squirrel
    Member

    Have you jacked up each end/corner, and spun the tires to see if they're true?

    What speed is the shake? It might be driveline, if it's a "fast" shake, at engine speed. Like I said, wheel speed is about 3 or so times slower than engine/driveline speed.

    It's really hard for us to know what you're describing, without being in the truck with you.
     

  5. Traditional spelling is Deth Wobble
     
    Texas Webb and Roothawg like this.
  6. pitman
    Joined: May 14, 2006
    Posts: 4,988

    pitman

    A sloppy king pin bushing fit is a poss. contributer.
     
    trollst likes this.
  7. seb fontana
    Joined: Sep 1, 2005
    Posts: 6,621

    seb fontana
    Member
    from ct

    I would get a king pin set and replace whats in the truck.
     
    trollst likes this.
  8. alchemy
    Joined: Sep 27, 2002
    Posts: 15,886

    alchemy
    Member

    Yep, start with the kingpins. When you have the bushings reamed, make sure they are using a ream that rides on the other side so the bushings are absolutely concentric to each other. Using a brake cylinder hone is a joke.
     
  9. blue 49
    Joined: Dec 24, 2006
    Posts: 1,277

    blue 49
    Member
    from Iowa

    I had a shake that started at about 60mph and went away as soon as I slowed down a bit. That was a bad tire. I mis-read my tape measure when setting toe once (was an inch off) and got the death wobble at speed. It wouldn't go away until my car was fully stopped.

    Gary
     
  10. dana barlow
    Joined: May 30, 2006
    Posts: 4,059

    dana barlow
    Member
    from Miami Fla.
    1. Y-blocks

    There some good tips already listed above by others!!,,;
    But here some extra;
    Drop axle use same specs as any straight axle{drop dose not matter,as long as it has been made right.
    Looking at the photos,things that were done a bit off,is rims have too much out set=high scrub/and that adds to any shake,by giving more leverage to any bump your tire hits. The shocks at there bottom mount are hook to shackle plate{ three hole type,and looks like shackle angle is wrong=spring is too long/or shackle axle bone was moved inward*I've see it happen,if wishbone was spilt an moved out to frame sides and someone heated shackle pretch< ahead of axle to line back up with spring<wrong way to do it=make space for stock spring too short.
    As for shocks,they will always work better if the bottom mount is out as close to tire as it can be/even 1in. wider helps.. Shocks with bottom mount close to center of car do nothing much.
     
  11. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,265

    Roothawg
    Member

    We had one at a certain speed. I would have sworn that we had a driveline issue. We checked driveline angle, tire balance, front end alignment, motor mounts, tranny mounts etc.

    It ended up being a brand new plug wire arcing on the header.
     
    squirrel likes this.
  12. ClarkH
    Joined: Jul 21, 2010
    Posts: 952

    ClarkH
    ALLIANCE MEMBER

    Start with the obvious, castor and toe-in, as squirrel noted. When I drove my car for the first time it had the death wobble. Checked the castor and it was 6 degrees (good). Checked the toe-in and it was an inch (bad). Reset toe-in to 1/8" and the problem was gone.
     
    Blade58 likes this.
  13. lostone
    Joined: Oct 13, 2013
    Posts: 1,376

    lostone
    Member
    from kansas

    Isolate the problem first...

    Simple steps first,
    1. Get it in the middle of the vibration, put in neutral and let off gas, does it go away? Yes? Then likely exhaust or drivetrain related. No change? Then likely front end.

    2. Do you feel it in the front or rear? Do you feel more in steering wheel ? Or seat ? Steering wheel- front, seat- rear.

    3.KISS, if tires are the same size all 4 corners rotate and see if it changes, if so it's tires, if not it's suspension. Next balance tires and see if that changes anything...


    NOW after doing the above if that doesn't find the problem now you can start changing alignment specs etc. BUT with a narrow vibration window alignment specs will probably do squat to change anything.

    My bet? Tires and/or balance. Possible belt moving in the tire at speed....
     
  14. Shawn Wildman
    Joined: Jul 8, 2018
    Posts: 23

    Shawn Wildman

    I think I'll start here and if they don't work ill move to the harder ones. I'm sure king pin questions will come later.
     
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  15. Shawn Wildman
    Joined: Jul 8, 2018
    Posts: 23

    Shawn Wildman

    *UPDATE*

    I took the two rear tires to the shop this morning and had them balanced (shake wasn't in the steering wheel, it was in the body). On the first wheel the guy removed a HUGE weight from the inside and another from the middle before balancing. The tire was 1/2 oz out on the inside, which took the smallest weight he had. It was the same story for the other wheel. I brought them home threw them on the truck and went for a ride. Vibration is almost completely gone.

    I suspect a balance of the front wheels will fix the rest.

    How does a shop get a balance job that far off?

    Anyways, thanks to everybody here for all the help!
     
  16. lostone
    Joined: Oct 13, 2013
    Posts: 1,376

    lostone
    Member
    from kansas

    Sadly I see it in our shop all the time.

    Glad to see you found it and it was something simple !



    Thats why I always start with the basics and go from there. ;)
     
  17. jnaki
    Joined: Jan 1, 2015
    Posts: 4,910

    jnaki









    Hello,

    Hope you get your hot rod wobble corrected. After 4 old cars back in the teenage, 20 something days, 2 1940 Ford Sedan Delivery vehicles, a 58 Impala, and a 1965 El Camino all having some kind of front end wobble at any speed. There were doubts as to what causes the problems. Tire balance and alignment was the first choice, then new bearings, suspension parts, even new shocks were all tried. Sometimes it corrected it for a while and other times, it did nothing.

    So, we went to our expert front end alignment guy and when we could not solve it ourselves, he did. The first thing we were told to do was tire shaving to get the tire round. No one wants to see 100+ miles of rubber sitting on the floor after the out of round tire gets shaved. But, not all tires are round. We had great brand names, Firestone, Goodyear, Inglewood Tire Co. and even Uniroyal were bought and tried.

    Each hot rod, cruiser had different kinds of speed wobbles and each time, something different was tried and completed. But, the solving matter was always back to shaving the original tire for a true round tire. Then the balancing got in the picture and finally the front end alignment. As hot rod/drag race guys, we had the new parts covered for pick and choose, similar to what lists have been provided.

    It was not us or the replaced parts, it was the tire not being round. When I bought the new set of wide Inglewood Redline Posatraction tires, they were brand new with new casings. After a 200 mile road trip, they were showing signs of high speed wobbles and the culprit was out of round tires.

    Jnaki

    Don’t disregard what others have said about tire shaving. It is a fact of life that not all tires are round. Our alignment guy said he wouldn’t start our project repair until the tires were shaved. He knew what he was talking about. Our 2nd 1940 Ford 327 powered sedan delivery was shaky when we bought it. After following his directions, that 1940 sedan delivery was the smoothest driving hot rod we ever had.

    Everything worked as it should and it all started with having to shave our, “so called new round tires.” Several trips to the So Cal deserts and Baja were on the floor after the tire shavings. Don’t worry, it all pays you back in the end.
     
  18. Shawn Wildman
    Joined: Jul 8, 2018
    Posts: 23

    Shawn Wildman

    Sound advice. Thanks.
     
    jnaki likes this.
  19. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 559

    MAD MIKE
    Member
    from 94577

    Incorrectly mounted on the balancer.
    Incorrect adapter used on the wheel to balance.
    Junk on the wheel mating surface or balancer surface.
    Water in the tire, even just a little bit.
    Monkey operating the machine...
    I've seen a fella mount a wheel backwards on the machine without any adapter. You think after adding the 5th biggest weight he would have stopped, kept going til the boss had to stop him after creating a beauty ring of lead. Bad day? Liquid lunch?
     
    ironrodder, fauj, guitarguy and 3 others like this.
  20. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,403

    Boneyard51
    Member

    I was going to tell how a shop can get a tire balanced wrong.... but Mad Mike beat me to it. He is spot on!

    That is why I recommend checking the balance!






    Bones
     
  21. Shawn Wildman
    Joined: Jul 8, 2018
    Posts: 23

    Shawn Wildman

    My next activity is to take the front tires and get them balanced. It would say its very likely the same Monkey balanced the front ones too. The truck still shakes a little, so I would guess that's the cause.
     
  22. sdroadster
    Joined: Jul 27, 2006
    Posts: 329

    sdroadster
    Member

    This is something I witnessed, and it has made me suspicious ever since.
    I was in the back room of a local tire shop, talking to a friend. The manager came back, and said "that customer is here to pick up his balanced trailer tires". Apparently the wheels hadn't been balanced yet, and the customer was waiting. A employee grabbed some wheel weights, and pounded them on the rim, and said "that job is done, he'll never know the difference".
    We pay in good faith, and you never know what takes place when we're not looking.
     
  23. Illustrious Hector
    Joined: Jun 15, 2020
    Posts: 72

    Illustrious Hector
    Member
    from Alberta

     
    jnaki likes this.
  24. Illustrious Hector
    Joined: Jun 15, 2020
    Posts: 72

    Illustrious Hector
    Member
    from Alberta

    I ran bias wide whites on my sedan they looked cool but shook. At one time, in our town, there were several tire shops that shaved tires before balancing. When the re-tread shop closed it was the last place that could do them. I ran the tires till they wore out and switched to five spoke wheels and radials.It was like driving a different car. I love the look of bias but won't run another set unless I find a shop that can shave them into "round"
     
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