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Technical caster angle

Discussion in 'Traditional Hot Rods' started by simon sinkinson, May 19, 2020.

  1. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    Hi
    I am still wrestling with the shimmy on my Model A . After having the steering box rebuilt it is wonderful and positive but I still get a awful shake at low speeds when I hit a bump .
    I bought a little inclinometer and tried to use it with a jig on the wheel but it was a bit vague .
    When I used the magnet to stick it to the axel I get a nice solid reading .
    Can anyone tell me if this position would be an accurate reading .
    Trying to get the truck up together to race at Pendine ( if it happens )

    Simon P1010049 (1).jpg
     
    dana barlow likes this.
  2. So you got 7.9*. Lots of good detail photos of you steering setup and you will get your answer. JW
     
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  3. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 772

    MAD MIKE
    Member
    from 94577

    If you can mount it to the top or bottom of the king pin itself, that would be accurate as it is the actual axis. A bump in the casting/forging can skew the numbers by a degree or more.
     
  4. jimvette59
    Joined: Apr 28, 2008
    Posts: 1,107

    jimvette59
    Member

    You need to record all three, Caster, Camber positive or negative and toe in. Check all your tie rod ends and drag link ends also king pins and spring shackle bushings.
    JMHO
     

  5. missysdad1
    Joined: Dec 9, 2008
    Posts: 3,305

    missysdad1
    Member

    Search "death wobble" and you'll get lots of helpful information on your problem.

    If the wobble persists after checking alignment factors, king pins, tie rod ends, etc. for worn parts which is usually where the problem lies, a steering damper like the one available from SoCal will probably cure it.

    The steering damper absorbs the first hit on the suspension and without that first excitement of the components the oscillation which follows will not occur.

    Good luck. This can be a very frustrating process.
     
    Last edited: May 19, 2020
  6. dodge35
    Joined: Feb 9, 2010
    Posts: 111

    dodge35
    Member
    from kentucky

    Toe in is different between bias and radial tires.
     
  7. Agree on checking toe in. Some additional pictures would also help. It appears you have a bunch of weight on that wheel shown for balance. May want to rotate the tire 180 on the wheel and see if the balance improves; i.e. you have the heavy spot on the wheel and heavy spot on the tire same place, move one to be opposite of the other. Also have you verified bump steer and ackerman?
     
  8. KenC
    Joined: Sep 14, 2006
    Posts: 1,045

    KenC
    Member

    I would prefer to measure the camber angle using hub face. There is a nice machined area there for the gauge. Turn wheel 20deg, a protractor and chalk lines on the floor work. Then calculate the caster angle. Rather than typing the process: just Google: calculate caster angle.
     
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  9. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,217

    ekimneirbo

    Get a copy of the Pete & Jake Catalog and they have a section that details how the steering components interact and what causes problems like yours.
    Some examples:
    Bump Steer 1 001.jpg
    Bump Steer 2 001.jpg
    Bump Steer 3 001.jpg
    Bump Steer 5 001.jpg
    This isn't Pete&Jakes but it was the source for this info............Get their catalog and it should help you find your issue.
     
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  10. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    Hi again
    I have done some more measuring from the face
    camber is 0.3 left side
    and 2.1 right
    caster is
    8.2 left and 7.7 right .
    I am going to borrow a friends tracking gadget to check tracking and order a steering damper .

    I enclose a few more photos . My tyres are very curved in profile P1010036 (1).jpg P1010027.jpg P1010024.jpg
     
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  11. dana barlow
    Joined: May 30, 2006
    Posts: 5,115

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

    Tire has too much PSI in photo,let some out/will need to play with it by feel,,but match both sides,adding a damper will help. Adding a panhard bar will help.
    Check readings of caster,should be same both sides/except if axle is twisted=that can happen if bones are mounted,at the rear of bone at other then same hight off ground*/can also happen if frame is leaning to one side. {other thing that may made caster not match,is a bent axle. Caster not matching can make death wabble start at a bump,but is not the only thing;tire PSI,tire out of round,out of balance,out of ture ect.,sloppy play any were.
     
    Last edited: May 21, 2020
    alanp561 likes this.
  12. hotrodjack33
    Joined: Aug 19, 2019
    Posts: 4,128

    hotrodjack33
    ALLIANCE MEMBER

    I fought the same occasional low speed "death wobble" in my old Sedan Deliv. for years. Tried a lot of different things...finally came up with the RIGHT combination.

    Caster positive 6 degrees, 1/32 tow OUT (an old t-bucket trick) and a So-cal steering dampner.
     

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  13. Moon50F3
    Joined: Sep 18, 2014
    Posts: 216

    Moon50F3
    Member

    Would you elaborate? I’m curious.


    Sent from my iPhone using H.A.M.B.
     
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  14. lostone
    Joined: Oct 13, 2013
    Posts: 2,820

    lostone
    Member
    from kansas

    If that's correct 0.3 camber on one side and 2.1 on the other you need to get that fixed too !!
     
  15. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    Any tips on getting the camber right after I sort out the tracking ?

    Simon
     
  16. hotrodjack33
    Joined: Aug 19, 2019
    Posts: 4,128

    hotrodjack33
    ALLIANCE MEMBER

    Camber is "built in" to straight axles and can't be adjusted (or at least easily by you). And the camber probably doesn't have much to do with the "death wobble" issue.

    A truck shop that works on big trucks & equipment may be able to help with the camber issue if it become necessary. My local Big Truck Shop can adjust camber and set the correct king pin inclination for the tire size you want to use.
     
  17. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    Fantastic article I now understand bump steer
    simon
     
  18. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    I have about 20psi in the tyres . What would be a good starting point for pressure ?
     
  19. Boneyard51
    Joined: Dec 10, 2017
    Posts: 6,442

    Boneyard51
    Member

    Fighting the “ death wobble” as some call it, can be frustrating! I’ve elaborating on this subject several times. Searching for the cause can prove frustrating. This problem had been around as long as the straight axle has existed!

    I maintained a fleet of straight axle vehicles, for over 33 years. I had three identical new vehicles, one was prone to shimmy after hitting a bump, the other two never offered to shimmy , ever. As stated, it was a brand new vehicle. Every component was checked with Digital equipment . All three checked out identical. Even swapped tires form a no shimmy vehicle. Didn’t change anything. I was at wits end trying to solve this problem.
    I asked an oldest guy at the old established front in shop in my town for help. He gave me some 2 degree shims for my axle. I put them in to increase my caste 2 degrees and the shimmy disappeared! I was happy and told the old guy what did! He said “ Boy, I told to too take 2 degrees out of the caster!
    I never changed that shim and that vehile is still on the road everyday today, with no problem.
    Since then I have “ fixed” many “ unfixable” front ends for people by simply changing the caster a few degrees to fit that peticular vehicle.
    My point is sometimes you can’t find the cause, you just have to fix the problem. That being said, all components need to be in good shape and everything set as close as possible, before adjusting the caster. Just my experiences.










    Bones
     
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  20. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    Thanks for that so great to hear from folk with experience . American Hotrods are rare in southern England so everything helps .
    Wish I lived in Oklahoma
    Simon
     
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  21. dana barlow
    Joined: May 30, 2006
    Posts: 5,115

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

    Old style tire only/not the new crap with no side wall.* just so some fool that uses those dose not show up.
    I said you need to play with !!!!! but about 15# as a start by your photo.
    Here a better then a guess;
    Tires really need to have air PSI done by the load on them. As we rebuild our cars,they end up ,in most case's at less total lbs. then they were,an often with tires size an type that were not on them as built. Point being; a factory tire PSI is void. So with a load on a tire it now really has= The thing to do is look at tires when its on the car,an see the shape. Looking at side wall near the road,you can see if a tire is going flat by the amount of swelling outward of that side wall. But also this same spot low on side wall with zero swelling=shows you have too much PSI, there needs to be about a 1/2in. of swelling or a little less. For the tire to act as designed. The tire is both part of the springs in car an its bit to the road. Too much air/PSI,and car rides hard and tire can't absorb a bump,so bounce over them,plus has less tread on the road,as contact with road is then a smaller patch=bad braking an poor cornering. Too little air/PSI and tire will flex too much,this builds too much heat in side tire,plus sway of car is feel bad an hold to road is less do to tire tread roll an left. Knowing those factors,should help playing with PSI make sense.
    Tire PSI is not the only thing that makes death wobble but dose add too it.
    On my race car,it's done by temp across the tire,at each side an center of tread. But I only eyeball it on my hot rod.
     
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  22. lostone
    Joined: Oct 13, 2013
    Posts: 2,820

    lostone
    Member
    from kansas

    Camber can be easily adjusted if you find a good shop. The axle will actually have to be bent to do it BUT it's not anything that's unusual. Straight axles have been bent since their inception.

    I still bend a good 10 or so a year on cars. Several dozen a year on semi's.

    But with that big of camber split you will have problems with tire wear AND that much camber it can easily make the car favor one way or the other. If it's positive camber it's likely the car will favor the side with the camber. If it's negative its likely to favor the other direction due to the negative camber pushing that direction.

    A perfect example is dirt track cars.
     
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  23. Inked Monkey
    Joined: Apr 19, 2011
    Posts: 1,834

    Inked Monkey
    Member

    Holy wheel weights batman! Thats a lot
     
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  24. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,217

    2OLD2FAST
    Member
    from illinois

    Do you have an overwhelming desire to be in a tornado ??
     
  25. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    I am now going to give the tracking a go . I will try 1/32 . Thanks for all your help .
    At the moment I have one tracking out and one in
     
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  26. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    Although this is really complicated I am enjoying the challenge of tracking .
    I need to start afresh with the tracking as everything is out. Have you any tips to get both ball joints straight before I get to the toe in ? I have centred the steering and fixed the steering wheel . got parallel string lines along the car .
    Is it then just trial and error with the track rod ends till I get it right ?
    Simon
     
  27. When checking Camber make sure the floor the car is parked on is level across the car.

    Most garage floor have some slope for drainage and if you had 1degree of slope your Camber could be close to equal or way way out.

    Same goes for caster if the rear of the car is low you will get a different reading to having the car level.
     
  28. Happydaze
    Joined: Aug 21, 2009
    Posts: 1,904

    Happydaze
    ALLIANCE MEMBER

  29. loudbang
    Joined: Jul 23, 2013
    Posts: 40,276

    loudbang
    Member

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  30. simon sinkinson
    Joined: Jul 19, 2019
    Posts: 52

    simon sinkinson
    Member

    My Steering damper turned up today and now I have just about got the tracking fixed I need to think about the damper . Has any one got experience of fitting one to this set up ? P1010020 (2).jpg P1010018 (3).jpg
     
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