traction bar w/ soa/reversed springs

Discussion in '40- & 55-Series Tech' started by pghfj40, Nov 9, 2005.

  1. pghfj40

    pghfj40

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    Hi everybody. I've coming out of long-time lurk mode cuz I got a question on my newly SOA'd :D FJ40.

    Watching the pinion when you get on it is kinda comical, but I'm afraid of what's gonna happen so I'm about to fab a traction bar sorta like Woody describes at
    http://www.ih8mud.com/tech/woody/wrap.html

    Anyway, since the rear springs are reversed, the pinion drops in an arc as the axle droops (since the short/stiffer spring side is to the rear), while a 3pt traction bar wants to move the pinion up in the opposite arc (about the bar's shackle mount). I imagine this binds/limits travel/causes stress/is generally undesirable.

    I'm trying to visualize different mounting points, or else two unequal arms, or maybe a single arm w/ a lower front mount... not arriving at anything I like though.

    Any thoughts from those that have this specific setup... have you found a geometry that will allow "harmonious" movement? Or did ya just build one & run it (that is: does it not limit/bind that bad in reality)?


    Thanks! -Ed '70FJ40
     
  2. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    Pinion movement is negligeable. Build a bar like woody's and call it done.

    BUT, don't use the bushings off of a shock..
    that was horrible work for the massa woodrow..

    ;)
     
  3. Trollhole

    Trollhole THC Supporting Vendor Moderator

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    WIth a shackle up front I don't think you will have a problem with what ever you design. It will make up for any descrepencies in angles in relationship to your pinion angle. Most SOAs I have seen use the cross member behind the transfer case as a mounting point. Some mount a totally new crossmember. Especially SBC conversions. The biggest thing to remember is to use the shackle. otherwise it will not last long and rip out. Like the PO did on mine. I'm rig of the week look at my writeup on mine. I wish I would have gotten the shackle up a little further but it's level with the skid plate.

    I have not noticed any bind or limit of travel using the wrap bar. A 3pt is the way to go. I used all hiem joints.

    With full travel I only noticed the shackle moving 1 inch back and forth. And trust me I have a lot of travel.

    [​IMG]
     
  4. pghfj40

    pghfj40

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    Another Q

    Thx for response. Glad it's not a big deal... keeps it simple.

    Already planning on larger bushings, but not sure which yet: I think I have some XJ LCA bushings laying around somewhere, & also some silicon filled ones from a '92 Z. Prb XJ... more common. Hope I didn't get overzealous last time I cleaned out the garage, though!

    Another Q: the goal w/ the front mount is to keep the shackle perpendicular to the line from the center of the axle to the lower shackle hole, right? Is there any reason that you'd want to cheat the angle one way or another? Again, just looking for practical experience to avoid the pitfalls...

    Thanks! -Ed '70FJ40
     
  5. bustanutley

    bustanutley

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    you are way, WAY over-thinking this. just make the shackle that attaches to the frame as straight up and down as you can with the weight of the truck on the axles this way the force is all up and down. Get the track bar as centered as practically possible on the axle. build it strong, and don't look back. Oh and stock rear 40 springs SO suck in my opinion. Get something longer that actually flex. Its not the wrap bar that is limiting the flex. ;)
     
  6. pghfj40

    pghfj40

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    Hey, I gotta do _something_ at work. :idea:

    Got it... thx.
     
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