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Technical Unsprung Weight Issues In Hot Rods: School Me

Discussion in 'The Hokey Ass Message Board' started by missysdad1, Jun 23, 2018.

  1. You've got perfect bumbsteer geometry.

    That radius tie rod link is scary and does the other side match?

    Death wobble is a violent left /right motion at the tires go back and forth. It will break your wrist at the steering wheel. Bump steer is not death wobble, with bump steer the pitman arm gets forced around as the suspension moves. The pitman arm will move the wheel around. Now if you white knuckle the wheel the car will steer if you let the wheel loose in your hand the wheel slips within your hands and the car goes relatively straight down the road if everything else is right.

    Worn king pin bushing can cause death wobble . Toe problems can cause death wobble. Oooohhhhh yeahhhhhh!!! Scrub radius causes toe problems and then the toe problems cause death wobble. 2" scrub radius is optimal, the more scrub then you need more toe, more toe and more problems.
     
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  2. F&J
    Joined: Apr 5, 2007
    Posts: 13,218

    F&J
    Member

    Dick never said that there is no solution to wobble, IF that is what you meant. He went through so many things that can induce wobble...and he even went into the big semi trucks that cannot get it, and explained that the "mass" and heaviness of all the heavy duty truck components "dampen" any ability for the wobble event to even start.


    I just came in now, and read your later word of ''oscillation" of the fronts...that sure does sound like the beginning movements that grow to become true death wobble, and if so, your scrub is just plain "out in left field".

    With the tire centerline so far away from that imaginary king pin line, that causes so much leverage as either tire hits something in the road surface...then it transmits that force to tie rods and drag links that can flex.

    One more thing to understand, is that "toe in" is set with wheels straight ahead, and most newbies do not realize the proper Ackermann has that toe-in condition, to change to toe-out as you start to turn. So, if a bump or hole in the road forces one wheel "out", you are at toe out, and if the caster is heavy like 7-8, the tie rod has to take more stress as it tries to move the opposite tire like the one that hit the hole. One wheel tries to play "catch up" with the other wheel, and then things start to flex, causing a violent chain reaction. Like Dick explained.... when that pothole event happens to a big truck, the components are all massive and very ridged, and this chain reaction cannot begin.

    The build is screwed up, many posters here can see that, so "if" you really think it might be the beginning part of a death wobble, try a damper. It is the simplest thing to try, as a diagnosis tool, if the car was not built right.. If the damper stops what you called as oscillation, then the damper installation has at least helped to diagnose the feeling you describe.

    .
     
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  3. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,065

    Blues4U
    Member
    from So Cal

    Personally, I would pull that front end and start over, including that steering box/mount. Those reinforced wishbones combined with the tube axle are a bad mix. If the tube axle cannot flex, and it can't, then the wishbones need to flex instead, or something has to. With the reinforcements the wishbones can't flex, so the energy is being transmitted into the frame, and the suspension is binding, not a recipe for good handling. The scrub radius if off, as others have mentioned. And the drag link/pitman arm are all wrong. And then the wishbone mount is scary looking. But that looks like a compromise arrangement because of the steering box placement. Man, it's all bad. Just bite the bullet and start over.
     
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  4. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,909

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

     
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  5. Stogy
    Joined: Feb 10, 2007
    Posts: 14,190

    Stogy
    ALLIANCE MEMBER

    MissysDad just to let you know Dick passed away in 2015 but he like several others were and are quite knowledgeable in such matters and their postings are invaluable to the hobby. Their memory and knowledge live on...
     
    Last edited: Jun 25, 2018
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  6. There is no "one" cause that's the same for every car. That's what he said.

    Death wobble starts from a bump and doesn't stop till road speed drops.

    Bump steer is different.
    Try this, jump up and down on the front of the car & watch the steering wheel. It should not be moving.
    Put a zip tie on the shock down to the body and see how far you can move the zip tie by jumping and driving.
     
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  7. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER


    As I've mentioned before, bump steer is NOT a major issue with this car, so can we please move on to the oscillation issue which IS a big deal...please. And yes, the steering setup looks pretty ugly but it works just fine. Same for the outboard radius rods. As was pointed out by bchctybob, my goal is to make this setup work acceptably well, not cut it all off and start over in search of perfection.

    It would appear from the many mentions on this thread that scrub radius is excessive and a likely culprit in causing or contributing to the cause of the oscillation. And, as dana barlow opined, the effective weight of the brake components increases the further away from the king pin it is positioned. Further, as F&J added, too much scrub radius also negatively effects the Ackerman to the point that this may be the root cause of a small bump turning into a large wobble.

    The combination of too much weight, too much leverage, opposing inertia forces and insufficiently strong components (thanks for this detail, Dick Spadaro) and we have, as Hnstray so eloquently put it, "incipient death wobble". It's been a community effort, but I think we've got something here that I can act on.

    Comments...?

    .
     
    Last edited: Jun 25, 2018
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  8. Unfortunately you cannot cherry pick one issue(scrub radius) and ignore all of the others. Everything has to work together.....and clearly it's not.
     
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  9. Death wobble doesn't stop.
    So if your issue does stop we can't call it that, because it's not. The term conjures a different thought process.

    Besides that, it sounds like you've got better ideas and closer to figuring it out than anybody else.


    If it were here, I'd advise you correct the empirically obvious defects and then re access any remaining problems. No way I'd let you spend your money on trying to get bad designs working.

    Those defects would be :
    (Not in any order)
    Steering box and mount -
    Tube axle and stiff radius rods
    Pitman arm issue
    Front radius mounts
    Parallel rear ladder bars
    Monster rear for light car
    Scrub radius.
     
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  10. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER

    That's not what I said in my last post. Sorry for not being more clear that I think it's the combination of the factors mentioned that are the cause of my problem:

    "It would appear from the many mentions on this thread that scrub radius is excessive and a likely culprit in causing or contributing to the cause of the oscillation. And, as dana barlow opined, the effective weight of the brake components increases the further away from the king pin it is positioned. Further, as F&J added, too much scrub radius also negatively effects the Ackerman to the point that this may be the root cause of a small bump turning into a large wobble.

    The combination of too much weight, too much leverage, opposing inertia forces and insufficiently strong components (thanks for this detail, Dick Spadaro) and we have, as Hnstray so eloquently put it, "incipient death wobble". It's been a community effort, but I think we've got something here that I can act on."




    .
     
  11. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER

    Points well taken. This is the kind of no-sugar-coating advice I give my own clients when they are set on making what I know is a bad decision. Most of the time it's because they are either tight, ignorant or stubborn - and sometimes all three.

    .
     
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  12. In What field do your clients seek services?
     
  13. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER

    And at this point I think I belong in the same group as the aforementioned clients... :rolleyes::rolleyes::rolleyes: But I'd really like to quit putting time and money into this car, shift my attention to the new car I'm building and just enjoy driving this one until the new one's done. We'll see.
     
    Last edited: Jun 25, 2018
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  14. Looks like you're doing a fine fine fine job on the Arin Cee roadster.

    So what do you see different on this one? Because it's not fine like the one you're building.

    You don't have to scrap all of it, but you'll be changing stuff. Selling stuff and buying, trading stuff.
     
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  15. Yes, I did read that, but you seem unwilling to address the possibility of steering geometry being part of the issue.
    By all means start with the scrub radius and see if that helps. It certainly can't hurt.
    I get that you don't want to tear the car down......you may just have to live with it in that case.
    Let us know how it goes.
     
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  16. roundvalley
    Joined: Apr 10, 2005
    Posts: 1,771

    roundvalley
    Member

    Do I see a steering stabilizer?
     
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  17. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER



    The black coupester is an old full-fendered street rod I bought off Craig's List knowing it had problems but underestimated the amount and extent of the poor workmanship. I bought it to "fix up" and drive so I could take my time building the new car. The more I've driven it the more little quirks have come to the surface like this one. I thought some new tires would fix the slight wobble, but the whole suspension has turned into a can of worms. I wish the only problem this car has was the suspension but it's more like peeling an onion - the more layers you expose the more you cry. :(:(:(
     
  18. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER



    Yes. Contrary to popular opinion a steering damper is not the magic cure-all for unruly front suspensions. They are a band-aid to keep "death wobble" at bay but do not cure the issues which cause it. Hell, if it worked I wouldn't be going to all this trouble, would I? :confused::confused::confused:
     
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  19. Stogy
    Joined: Feb 10, 2007
    Posts: 14,190

    Stogy
    ALLIANCE MEMBER

    A great percentage of the Hotrods since inception have been geometrically off...its just part of the evolution. When buying Homebuilt and for that matter many Shop Jalopies...they are engineered by assumed and learned technical lingo and experience or lack thereof...some is non critical and some could kill...:eek:.
     
    Last edited: Jun 25, 2018
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  20. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,065

    Blues4U
    Member
    from So Cal

    Pardon me if I don't put too much faith in his methods of weighing the parts and remain skeptical.
     
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  21. Fordors
    Joined: Sep 22, 2016
    Posts: 2,300

    Fordors
    Member

    Well with only an old postal scale with a four pound limit and a bathroom scale available the best way seemed to be to hold the parts while weighing myself and then subtracting my weight. OK, I’ll grant you it was not done on a scale approved for weighing things for retail sale but what do you question about this method?
    Edit- the drum brake was weighed as an assembly complete with a ‘40 round back spindle as removed from an axle years ago. Rather than disassemble it I separately weighed a ‘42-‘48 square back, it weighs five pounds so that was subtracted from the initial value of 39#, giving a weight of 34#. OK, the square back is a bit heavier than the round back but it couldn’t be very much. What would you find suspect with this method?
     
    Last edited: Jun 25, 2018
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  22. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,065

    Blues4U
    Member
    from So Cal

    I don't have the parts around to weigh, and I don't have a proper scale either. If I had the parts I would have to do the same method, what I'm doubting to begin with. I'm trying to do it the lazy way, using google search. I'm finding claims of both on different sources, some saying the drums were lighter, others saying the discs were. Doesn't seem to be a firm consensus out there either way.
     
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  23. Fordors
    Joined: Sep 22, 2016
    Posts: 2,300

    Fordors
    Member

    In the claims you found did anyone state hard numbers or just speculation? What the eye and mind might perceive is quite different than what the scale says.
    I’m done here, none of this helps the OP arrive at any solutions and is just muddying his thread.
     
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  24. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,065

    Blues4U
    Member
    from So Cal

    Why do you ask a question and then say you're done. Did you want a response, or was that rhetorical? The answer is I found some pretty hard numbers, but they did not specify how they came up with them, no details. And they were not 40 Ford drums vs mid or full size GM disc, so probably not really appropriate here.

    I think this is a wild goose chase for the OP anyway. I think his problems are elsewhere than the unsprung weight of the brake assy's. Even your measurements don't show enough of a difference to account for the complaint he has, and it's not been a problem for others, so again, wild goose chase.
     
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  25. Please please please forgive the OT subject vehicle and observe the death wobble. It's the exact same on our hotrods.
    It's pretty common on these vehicles and much of the science is the same for our type of rides. Its very easy to research the required repairs and causes on these vehicles. I'm not making a video with a hot rod as the subject matter. So do your own research. You'll find that it's a combination of increased scrub radius, caster changes and slightly warn components and bump steer geometry. Those conditions may be arrived at differently but the condition and symptoms produce the EXACT same results.

     
    Last edited: Jun 26, 2018
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  26. F&J
    Joined: Apr 5, 2007
    Posts: 13,218

    F&J
    Member

    That video should have been put up on each of the many wobble threads over the years. That one is better than others for the reason of showing them using a small object to hit with one tire.

    It is now should be easy to understand that if the scrub is way off, then as that tire hits the object, simple physics will force that passenger side tire to steer HARD to the right! Then, that tire/wheel "tries" to get the drivers side to steer the same, BUT if the caster is too heavy, then that driver side will resist steering, as heavy caster wants that wheel to run straight ahead. That resistance will cause the flexing of components, which makes the parts unable to solidly connect both tires in unison.

    My thoughts on this particular video, proves the importance of getting the scrub correct, if it is WAY off. The "4x4 world" wobble "usually" is a result of swapping on big tires with very wrong wheel offsets...AKA incorrect scrub radius. The stock damper keeps the wobble masked, but eventually, the components wear out and the wobble gets far worse to the point of needed repairs.

    But if you have too little caster, I would think that if having the same scrub error , then hit that object, the lack of any caster will have the wheels not trying to stay straight in the first place. That assumption comes from the fact that most all cars do have positive caster to keep the car from wandering. All cars have different caster settings if you look in manuals, so it is total BS to use the old hotrod wives tale of 7 degrees. It must be determined for each build, different steering ratios, bias vs radials, engine weights or lack of...you name it.

    .
     
  27. When fabricating a chassis you must have a target where caster is going to be.
    7 is a good target. The "seven" target comes from the average of the factory recommended 4-9* in completed form. Not that 7 is the absolute best setting for drivability concerns (it very well may be) but a fabricator needs a target and from there adjustments are made with a fair amount of time between fabricating in 7* and actually driving it at 7* looking for improvements.

    The point is don't HATE the caster setting of 7 or discount it- but keep it in its proper place of a starting point,
     
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  28. blowby
    Joined: Dec 27, 2012
    Posts: 6,116

    blowby
    Member
    from Nicasio Ca

    The old Blazer 4x4s (solid axle) came stock with a steering stabilizer. Mine was missing when I got it, terrible death wobble. Put one back on, problem solved. Didn't like the idea of a 'band aid' fix but it was good enough for Chevy..
     
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  29. F&J
    Joined: Apr 5, 2007
    Posts: 13,218

    F&J
    Member

    Yes, it sure is the midpoint of Ford solid axle specs in my old Motors Manuals. ...but... we build cars from different components!!.

    but take a look at car brands in that same manual and you will see that most solid axle cars back then ran 2 or so, I did find just one at 3, I think.

    The "Target" needs to come from looking at the components used in that one build in front of you....not some midpoint of specs on "stock" Fords!...so when we screw up and go with 7 due to lack of setting caster to each mix of parts... the 7 is just like throwing a dart out at the wall.


    You guys will shit when I tell you where my caster is on my 32. I did a "rear" ride height change a few months ago, (which slightly changed my "as built" caster setting) so I will put it back on the tables to check it with real alignment equipment, not just an angle finder on the beam on an imperfect shop floor.. I am tied up right now, but I bet it is ONE degree! The car tracks great, and yes, it is on 40 year old firestone bias fronts! Lmfao..(They WERE supposed to be mock up tires,..but...) lol

    Why did I shoot for roughly 1.5 during the build? Simple...I run a very heavy early Olds Rocket, AND a wicked fast ratio steering box...2.5 turns lock to lock at the Ford original axle limit stops! So, if I ran 5, I simply would not be able to park the damn thing!

    Ok, another 32 I did for Harleycontracter ( Paul) We used his choice of a mint 556 F100 box, which is a very slow ratio, a heavy early Cad motor, so I went with 5 to get some decent road feel. If I went lower, that car would be drifting as you kept lightly steering in normal roads that are not straight like the salt flats. You would be constantly "sawing the steering wheel" with lower caster.


    I swapped thoughts with Dick on here many times, and towards the end of his career here, he then leaned towards 5 as the start point for a average build...

    Heavier caster causes problems...too long to explain on a busy day here..

    .
     
  30. missysdad1
    Joined: Dec 9, 2008
    Posts: 2,781

    missysdad1
    ALLIANCE MEMBER


    Good post! Good video! Lots of info...but slightly inconclusive IMHO, as are a couple of other 4x4-related videos on the same subject. These videos (made by people who sell parts) seem to point at worn parts being a necessary component of the combination of problems which cause death wobble. Which begs the question: If all components are fresh will the single factor of excess scrub radius cause a death wobble by itself?

    Obviously the answer is no, because there are countless 4x4s and hot rods running around with deeply reversed wheels which have the effect of moving the scrub radius outward which are not having the problem.

    Which then begs the next question: If the steering damper was removed from all these vehicles with fresh suspensions and deeply offset wheels would they then be subject to death wobble if conditions are right - ie. hitting a 2x4 in the same manner as in the video.

    It would seem that the answer to this question is yes, especially if one considers Dick Spadaro's input which says that vehicles with super-strong front end components are not subject to death wobble because the components themselves cannot flex regardless of the forces put on them. Hmmmm....

    We must also consider an additional question: Would those vehicles subject to death wobble when the steering damper is removed still be subject to it if they were fitted with normal offset wheels with normal weight OEM tires?

    Or, is it the combination of increased scrub radius AND increased wheel/tire weight that induces the death wobble, AND the lack of a damper allows the wobble to grow and become uncontrollable BECAUSE the insufficiently strong suspension components aren't strong enough to prevent it.

    Lots of food for thought here.

    .
     

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