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Technical Front suspension/frame set-up help

Discussion in 'The Hokey Ass Message Board' started by bobbytnm, Aug 5, 2017.

  1. bobbytnm
    Joined: Dec 16, 2008
    Posts: 1,508


    I'm attempting to fabricate a frame for my 26 RPU project with 2" x 3" rectangular tubing. I'll be using a stock 38 Ford suspension without splitting the wishbones (hopefully) and a Model A front Xmember. I'll be running a basic ladder type frame similar to Model T or Model TT with no kick-up front or rear
    I understand that the front Xmember should have (has built into) about a 7 degree angle to it.
    My question is where to locate the ball mount for the wishbone in relation to the top of the frame rails? Where was the wishbone ball mount originally? was it on an Xmember or on the bellhousing?
    Either way, I need to know where the wishbone ball mount is in relation to the front leaf spring mounting pad.

    I tried looking at the following frame dimension drawings for Model A's and 35-40 Ford passenger cars. Maybe its me but I don't see the wishbone ball mount on either one of these drawings


    Thanks everyone
  2. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,792

    Member Emeritus

    The ball mount would be in front of the piece making the "X".
  3. bobbytnm
    Joined: Dec 16, 2008
    Posts: 1,508


    Thanks. Would that mean the ball mount is even with the bottom of the frame in that area?
    If so, then from the top of the frame, in THAT area, it would be 5 1/2" below?
  4. Your going to have to modify the bones,at 7 degrees your un-split bones will most likely be lower as you tilt the axle forward. HRP

  5. bobbytnm
    Joined: Dec 16, 2008
    Posts: 1,508


    I'm guessing on the 7 degrees. I haven't actually measured the Xmember yet. Its a stock Model A Xmember (29 or 30 maybe).
    I guess another way to ask my question is, what angle should the wishbones be in relation to the top of the frame?

  6. Mr48chev
    Joined: Dec 28, 2007
    Posts: 31,296


    1929_Ford_Model_A_chassis-engine_rightBut.jpg 1929ModelAFordSpeedster-may1eBut.jpg Are you running the spring in front of the axle or changing spring perches and running a spring above the axle? That would make a difference in height.
    Unless the engine and trans are sky high in the frame the center crossmember that the wishbones will hook to will be down several inches from the bottom of the frame rails. Since you aren't running some wild suicide front end it isn't going to be super low at the rails anyhow.
    I took the liberty of jacking these two photos off the net of near stock Model A chassis where you can see the wish bone below the rail and how far. OOPs they might be above the text rather than below.
    Last edited: Aug 5, 2017
    Joined: May 8, 2010
    Posts: 345


    The ball end cup is at the bottom front of the X support.
    If you are fabricating a new chassis from box RHS none of this really matters.
    The key is at ride height the castor of the front axle is around the recommended castor angle for your use, 5 - 7 degrees, Castor is always referenced to the road.
  8. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,572

    Sheep Dip
    from Central Ca

    It's really just simple math to set it all up. Tack it all in place and double check/verify sitting on the wheels before welding.
  9. bobbytnm
    Joined: Dec 16, 2008
    Posts: 1,508


    Thanks all
    I'll be running the '38 front suspension totally stock (spring in front of the axle). If the ball mount for the wishbone is indeed located at the bottom side of the frame at the front X support then I should be able to figure out its relative position in relation to the spring mount. I should be able to account for the kick up in the 35-41 frames.
    From looking at the line drawings above it looks like the total distance from the top of the frame at the front kick up to the bottom of the frame at the center is 8 1/4".

    My 1st instinct was to get the Model A Xmember tacked into place and bolt the axle up and see where it ends up, but, since I haven't replaced all the worn parts in front suspension there could be quite a bit of error involved.

    Heck, I'm probably overthinking this whole thing. Thanks again for all the help

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