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Technical dropped axle twist question

Discussion in 'The Hokey Ass Message Board' started by gearheadbill, Oct 4, 2018.

  1. gearheadbill
    Joined: Oct 11, 2002
    Posts: 1,308

    gearheadbill
    Member

    Working on putting a new front susp. and steering in a 34 Ford. Today a friend was talking about a death-wobble situation and something he said made me go back and check caster on each side. I have about 1.5 degrees differing caster side-to-side. See pics. I have no idea what the axle I have is other than it's a new axle, not Ford OEM. I know many will say that an original Ford axle is the best to use, and I'm sure they're correct. I just don't happen to have one and would like to use this one if possible, but certainly will replace it if I must.

    What is an acceptable amount of caster difference side-to-side? Thanks.

    P.S. Just in case anyone has a question, I'm using a precision ground V-block clamped to the new king pins and bushings, then a perpendicular ground steel bar to set the angle finder on. King pins fit spindles really nice with no slop. Also 33-34 split wishbone with adjustable perches etc...no twist forced onto the axle.
    driverscamber.jpg passengercamber.jpg
     
    chryslerfan55 likes this.
  2. I always run 7 degrees and both the same, never a problem.
     
  3. Lockjaw
    Joined: Sep 1, 2003
    Posts: 167

    Lockjaw
    Member

    heat it and bend to match -just let it air cool
     
    chryslerfan55 likes this.
  4. Fordors
    Joined: Sep 22, 2016
    Posts: 3,401

    Fordors
    Member

    A simple solution but it assumes it is not a cast axle.
     
    gimpyshotrods and Unkl Ian like this.

  5. Possible variation between the split bones, or the rear mounts ?
     
  6. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,181

    jaw22w
    Member
    from Indiana

    You probably already know this, but the level must be aligned parallel with the centerline of the chassis when taking the reading. A slight turn of the level can produce the kind of readings you are getting.
     
    F&J likes this.
  7. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member

    try turning the axle around to prove that the bones are not the problem, and prove that the axle is off.

    I am fairly sure you'd want less caster on the gutter side, as I think right now, the completed car may want to "pull" to the gutter side.

    .
    very true.
     
    Hnstray likes this.
  8. brigrat
    Joined: Nov 9, 2007
    Posts: 5,360

    brigrat
    Member
    from Wa.St.

    Is the rear level?
     
  9. lostone
    Joined: Oct 13, 2013
    Posts: 1,526

    lostone
    Member
    from kansas

    After you have double checked everything as stated above and verify that it is indeed 1.5 degrees different then find a old school shop and see if they have the tooling to change caster.

    I would shoot for 1/4° to 1/2° more caster into the right wheel to make up for road crown.

    A side note, if it's a cast axle you won't be able to use caster tooling on it.

    It's a fun process ;) done it numerous times over the years.
     
  10. I type too slow. Lostone beat me to it.

    Having aligned hundreds of straight axle trucks, I set caster at 1/2° more on the right than the left, with total at 4-5° +. The variation let the truck run straight against the road crown with no drift (with nothing else like rear end alignment or worn tires affecting it). Too high a variation and any twist put in to the axle will make one side fight the other at every bump in the road. It looks like you have adjustable perches, so that would eliminate any spring twist.
    We had tooling to correct axle twist. Like Lostone said, it's lots of fun!!
    If it's a forged axle, you're good. If not, you're SOL.
     
    Last edited: Oct 4, 2018
    lothiandon1940 and 302GMC like this.
  11. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,640

    thirtytwo
    Member

    i Would verify the wishbones are the same before I would even think about bending the axle to match, it wouldn’t take much difference at the bone to make a degree
     
    Benny's Ford and lothiandon1940 like this.
  12. Good point!
     
    lothiandon1940 likes this.
  13. Is the chassis dead level, side to side, where the split bones mount ?
     
  14. gearheadbill
    Joined: Oct 11, 2002
    Posts: 1,308

    gearheadbill
    Member

    Some very good comments. Thanks

    Pretending for a moment that everything is plumb and level, all components (other than the axle) are as required etc., I am taking it that the 1.5 degree difference in caster from side to side would concern you fellows enough to stop and get both kingpins to lay back equally before moving on. That is: 1.5 degrees variation is too much no matter where its coming from.

    I've probably put together 12-15 axle chassis for my own cars with nary a problem: they've all driven very well. But all have used either new axles, mainly Chassis Engineering, or a quality drop job from Greg at Anson. I guess it's possible this axle may even be a Hoffman Group shite product. Since I don't have any idea as to it's heritage, I'm suspicious enough to try another axle. I'll re-check a few things first, swap the axle side to side first etc.. I'll get back to this thread with an update ASAP.

    Thanks again.
     
    pitman, Hnstray and brigrat like this.
  15. Corn Fed
    Joined: May 16, 2002
    Posts: 2,941

    Corn Fed
    Member

    Others may disagree with me, but I personally would not loose sleep over 1.5 degrees on a street driven car. Maybe if you were gonna run at Bonneville 200MPH, but not something that's gonna go over normal roads. Have you ever seen how much a dropped Henry axle with split bones and a hoop steering arm flexes as it turns or goes down the road over bumps? If 1.5 degrees scares you, you don't wanna know what's really going on.
     
    RICH B, RidgeRunner, 117harv and 2 others like this.
  16. alchemy
    Joined: Sep 27, 2002
    Posts: 16,546

    alchemy
    ALLIANCE MEMBER

    What about all the guys who can't agree on what the optimum angle is supposed to be? Some say 5 degrees. Some say up to 7 degrees. You have the spectrum covered with just one axle. ;)

    I wouldn't worry about it either.
     
  17. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,500

    Mr48chev
    ALLIANCE MEMBER

    On the wish bones putting a twist into it thing. That should be reasonably easy to check.
    I've got to agree with Hotrod A on the having slightly more caster on the right (curb) side to compensate for road crown. That is the fine tuning to have it drive straight down the road an not drift thing.
    If the front end wasn't that far together I'd be inclined to pull the axle out and set it in some sort of fixture to see if the difference is in the axle from the get go or if the bones might have caused at least part of it.
     
  18. brigrat
    Joined: Nov 9, 2007
    Posts: 5,360

    brigrat
    Member
    from Wa.St.

    In measurable inches or fractions 1 1/2 deg. isn't much close to center but take that same 1 1/2 deg. and apply it outward to the tread and you have a magnified distance...........................................
     
  19. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,500

    Mr48chev
    ALLIANCE MEMBER

    A close look at his first post shows that he has a pretty advanced angle finder (caster gauge) hooked to his king pins to measure directly off the king pins.
    He is pulling the angle directly off the king pins.
     
  20. brigrat
    Joined: Nov 9, 2007
    Posts: 5,360

    brigrat
    Member
    from Wa.St.

    Yep, I seen that.............................................
     
  21. lostone
    Joined: Oct 13, 2013
    Posts: 1,526

    lostone
    Member
    from kansas

    Just be aware with that much difference in caster angles side to side it's probably going to pull away from the high side. So if you have 1.5 more in the right side it's going left and vice versa.

    Actually the extra 1.5 caster will push the car the other direction.

    On a straight axle that's a lot of split.
     
  22. Yep. On a low crown four lane, it will drift left from the far right lane with 1.5° variation, more so in the fast lane. First step is to determine forged or cast...….then fix or replace.
     
  23. gearheadbill
    Joined: Oct 11, 2002
    Posts: 1,308

    gearheadbill
    Member

    Getting back to this after some additional checking. It's all my fault!!

    I had a small burr on one edge of the v-block (shiny dot near the v) I was using to check camber with. With the burr up, the digital level would rock or sit a bit different than when I flipped it over and used the other side up. Deburred the v-block and camber fell in within .5 degree. Panic is over. I REALLY appreciate all the helpful comments. Thanks! 20181005_172254_resized.jpg
     
    Unkl Ian and F&J like this.
  24. Good deal! Dontcha' love it when it's an easy fix!
     
  25. RidgeRunner
    Joined: Feb 9, 2007
    Posts: 886

    RidgeRunner
    Member
    from Western MA

    Thanks for posting your findings. Far too many let their posts fade away and leave inquiring minds continuing the need to know.

    Neat jig set up, especially for checking just the axle itself prior to any assembly at all, adaptable for kingpin inclination/camber check as well.

    Ed
     
    Last edited: Oct 8, 2018
  26. gearheadbill
    Joined: Oct 11, 2002
    Posts: 1,308

    gearheadbill
    Member

    I love it that it was so simple....hated it cuz it was so simple also. A little dumb and happy at the same time.
     

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