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Rear Wishbone length

Discussion in 'The Hokey Ass Message Board' started by Blue One, Sep 6, 2010.

  1. Blue One
    Joined: Feb 6, 2010
    Posts: 7,314

    Blue One
    ALLIANCE MEMBER
    from Alberta

    I have read the threads discussing where to locate the rear wishbones for best suspension working. I know that the best is to have the rear wishbones go forward and meet near the tailshaft of the trans in the middle of the frame.

    I however am not going to do that. :) I have seen plenty of T roadsters etc. with the rear radius rods or wishbones mounted on the outside of the frame rails and they work fine.

    I want to do that on my 26 RPU build as I want to match the look of the front wishbones I fabricated.

    So when I build them I am going to have them run along the frame rail and mount like I did the front.

    The question is, how long should they be ? Any magic formula, or should I just make them a length that will give a balanced look as compared to the length and mounting point of the front wishbones?

    Ideas or info ? ( You can look at my build thread if you want to see the front bones I built)

    Larry.
     
  2. F&J
    Joined: Apr 5, 2007
    Posts: 11,352

    F&J
    Member
    from CT

    If you want proof that they don't work fine, try this:

    -unhook one rear of your front bone on an I beam axle. Now pull up and push down and look and FEEL what happens.

    - then try that with the rear setup you plan.
     
  3. Antny
    Joined: Aug 19, 2009
    Posts: 1,071

    Antny
    BANNED
    from Noo Yawk

    Shouldn't they pivot in line with the driveshaft front u-joint.... to keep everything moving in harmony?
     
  4. Blue One
    Joined: Feb 6, 2010
    Posts: 7,314

    Blue One
    ALLIANCE MEMBER
    from Alberta

    Well, we could debate all day about it, but I have a buddy with a T roadster pickup and his radius rods run along the outside of the rails just like I plan.

    His car has been on the road for a dozen years and rides and drives fine.
    If you look at the numerous T roadster threads on here you will find a whole bunch of cars built that way, old time cars built back in the day and some newer ones.

    So, how about length :rolleyes: ????
     
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  5. F&J
    Joined: Apr 5, 2007
    Posts: 11,352

    F&J
    Member
    from CT

  6. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,462

    thunderbirdesq
    Member

    I'm with Frank... Setting them up like that is a BAD idea. There have been more than a few threads on here by guys with cracked/broken/bent rear bones. The first problem is that they weren't designed to withstand the torque of braking and acceleration, that's what the torque tube is for. Spreading the front mounting points only worsens the problem by increasing stress on the connections, turning your whole rear axle into a anti-sway bar of sorts. While I will agree that there have been plenty of cars built in this manner in the past, it doesn't mean it's a good idea. Especially when there are PLENTY of other more functional alternatives. This includes using them as the lower links in a three-link setup, which keeps the look but articulates and holds up much better.

    If for some reason you just can't stand to do it any other way, beef them up at the mounting points, keep your eye on them with periodic examinations, carry your lucky rabbit's foot, and cross your fingers!! I'd make them as long as possible... Less pinion angle change per degree of suspension articulation.
     
    Last edited: Sep 6, 2010
  7. Blue One
    Joined: Feb 6, 2010
    Posts: 7,314

    Blue One
    ALLIANCE MEMBER
    from Alberta

    So what does a three link setup look like ?
     
  8. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,462

    thunderbirdesq
    Member

    You'd fab new mounting system for the lower links that can pivot on the axle, then a third -usually triangular or wishbone shaped top link mounts to the pumpkin. Do a search, lots of info on here. And... Check out the link that F&J posted, Nimrod's roadster used a pair of '36 rear radius rods (the beefiest) as the lower links of a four link setup.

    Shouldn't make a difference, that's why there's a slip yoke to make up for the difference in arcs.
     
  9. Antny
    Joined: Aug 19, 2009
    Posts: 1,071

    Antny
    BANNED
    from Noo Yawk

    Good point. Does this apply to a torque-tube setup as well? That's what I assumed (why, I have no idea!) he was running.
     
  10. SUHRsc
    Joined: Sep 27, 2005
    Posts: 5,075

    SUHRsc
    Member

    On race cars they were mounted to the outside of the rails at the same spot as the pivot of the ball socket on the front of the torque tube. The idea was that the rear axle acted as a sway bar, fighting against the twisting motion from unequal road surface.

    Most of them switched to a Chevy type slip joint at the front of the torque tube also.

    This isn't ideal for the street due to the wear/stress on the parts.
     
  11. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,462

    thunderbirdesq
    Member

    On a closed drive setup they mount right to the torque tube. The only pivot is at the TT mount behind the trans. They only reason to split them if you're running closed drive is for the sway bar effect like Zach mentioned. Built-in stress, if you will. NOT good on a street driven car.
     

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