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Adjustable rear spring shackle

Discussion in 'The Hokey Ass Message Board' started by Jmountainjr, Dec 4, 2011.

  1. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 886

    Jmountainjr
    ALLIANCE MEMBER

    I know this won't be for everyone, but thought I'd post it anyway as there are many "semi-traditional" rods on here. I'm running a traverse rear spring with.....a traingulated four link. Anytime you mount the rear spring to a flat crossmember, the spring height and/or ride height shims move the axle to the rear due to the frame rake. Plus with all of the adjustability in the four link I wanted to be able to adjust for any spring binds. You could also use this on a traditional transverse spring if you just needed to tweak the wheelbase to get the tire better adjusted in the wheel well opening. Anyway it's just a rear shackle that is wider than the spring that will accept spacers to adjust the spring to perch relationship. In my case it's 3/4" wider. The picture showes the worst case with all of the 3/4" adjustment on one side. You could run spacers on both sides to get something less than a 3/4" adjustment.
     

    Attached Files:

  2. I'd be interested in seeing some pictures of the whole rear suspension. There's some pretty tricky geometry involved, as the spring and top links are both trying to control side movement and roll center.
     
  3. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 886

    Jmountainjr
    ALLIANCE MEMBER

    The top link brackets are not yet welded to the housing, but this is the basic layout.
     

    Attached Files:

  4. That's some nice fab work.

    Have you tried or seen this combination used before? I teach this sort of thing on a daily basis, and over the years I've tried to get the best possible understanding of the forces involved in suspension systems; and I see a potential problem with the geometry. It has to do with the location of the roll center of the 4 link.

    If you're not worried about it, I'll leave it alone.
     
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  5. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 886

    Jmountainjr
    ALLIANCE MEMBER

    There have been a number of threads on here about the triangulated four link and a transverse spring. Most get to the point that with a light car - in this case a roadster- and a relatively small suspension travel, it works OK. Some say very good. I thought about delinking the ends of the springs like a early Corvette, but decided to keep it traditional looking. I would be interested in your comments as I know that any significant binds etc. break parts and cause erratic handling.
     
  6. You are right, the limited travel will probably negate the issue.

    The point at which the top links converge determines the roll center (the "fixed point" around which the housing revolves); and with the wide spread you have on the housing mounts, that point is actually a couple of feet behind the housing. That means the geometry is going to give you a fair amount of side motion of the housing during one-wheel bump or chassis roll. The shackles will only allow a limited amount of motion before they run out of arc, and at that point the suspension will go into a bind.

    The Tri-4 link is an excellent suspension design, you just have to be careful about not having any conflicting forces at work with it...
     

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