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Wishbone and steering questions

Discussion in 'The Hokey Ass Message Board' started by bigblock69n, Feb 24, 2010.

  1. bigblock69n
    Joined: Oct 30, 2009
    Posts: 63

    bigblock69n
    Member

    I have a couple questions about my suspension and steering geometry. I have read on here that with cowl steering(which is what i plan on using) that the steering rod from the box to the axle should be the same length as the wishbone and also run parelel to it to keep bumpsteer at a minium. Is this true and if so does any body know the different length of the different year wishbones I am going to need 40 inchs and the ones i have are only 34 inches. Thanks
     
  2. loudandfast13
    Joined: Mar 19, 2008
    Posts: 175

    loudandfast13
    Member

    You need to keep everything on the same arc. The steering arm should be the same length and parallel. Later bones tend to be longer than model a bones. I have several sets of longer wishbones if you are ever around metro Detroit.
     
  3. bigblock69n
    Joined: Oct 30, 2009
    Posts: 63

    bigblock69n
    Member

    thanks alot for the info
     
  4. bigblock69n
    Joined: Oct 30, 2009
    Posts: 63

    bigblock69n
    Member

    So does my wishbone and steering shaft need to be the same length or just on the same arc?




    Thanks heading to the basement at COBO see ya there
     

  5. bct
    Joined: Apr 4, 2005
    Posts: 3,154

    bct
    Member

    just the same arc...or parallel to each other...length is less of a concern
     
  6. If they were parallel they would not swing in the same arc.
    Bill.
     
  7. The length is what makes it the same arc. You want the steering arm and 'bone to from a "parallelogram" like a 4 bar suspension, but they don't have to be mounted right above one another. Here's a pic of my (non-trad) rod project showing the steering link and hairpin relationship.
    [​IMG]

    One of the problems you will have to deal with in a cowl steer setup is how long the pitman arm off the steering box needs to be to get the steering link down parallel with the 'bone... If you just go with a LONG arm, the steering will be very fast. A lot of guys use a raised arm on the knuckle to get the link level, but it better be built really strong...
     
  8. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,254

    Hackerbilt
    Member

    To get the same relative arc on a stock wishbone or split wishbone the frame mounted steering box drag link is aligned along the same line that is created by the wishbone as it moves up and down.
    The ultimate location would be to have the pitman arm tierod end exactly in line with the tierod on the end of the split wishbone, but the actual available suspension movement of the vehicle usually makes this unecessary. Along the projected line works fine...as Ford themselves did it.

    With a 4 bar its placed on the same angle as the 4 bar links...usually level with the ground...and preferably the same effective length. This allows the drag link to perform just as the 4 bars themselves with no bumpsteer.

    Cowl steering relys on the wishbones and drag link being so long that, even though the wishbones and draglink scribe very different arcs due to the height separation, the variance is negligible over the range of available suspension movement.

    Use a 12" ruler to scribe an arc 3" above level and 3" below...then do the same with a yard stick...moving the pivot point back 2 feet so that the scribes overlap.
    The yard stick scribes a much shallower arc...as would a draglink mounted way back on the cowl.
    The long wishbone arms and drag link simply run out of suspension movement before the bumpsteer issues become apparent in most cases!
     

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