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Front Coil Over Questions???

Discussion in 'OffRoad Design' started by 87GMCJimmy, May 9, 2002.

  1. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    I been thinking about this and had a couple of questions even though it will probably never happen on my truck...but I can dream can't I.

    What are the disadvantages to setting up a radius arm suspension like the furds. The arm is solidly connected to the axle. I read Steve's Frisbie's write-up and he's says that he has unequal length links that give axle rotation just like the radius arms would. With the radius arms you could eliminate the third link and a bunch of heim joints which would lessen the cost. Also, any guess on the maximum range of motion a stock style furd radius arm mounts has?? The idea would be to use these at frame attachment point instead of heims. I'm just trying to think up ideas to bring down the cost and complexity a little but still make it worth while to do. I realize that this setup would be less flexy that the complete heim jointed system but it would bring the price down quite a bit also.

    Thanks for letting me ramble.....
    Mike
     
  2. DougP

    DougP Registered Member

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    I'm hoping somebody else will come in with more data, but here is what I've discovered so far in my project. I'm converting a 1995 Dodge Dakota from IFS to straight axle. I plan to use the ford style suspension, but not the stock parts. There is a limit on travel for the stock radius arms but I don't have the details. I will probably use one of the aftermarket long travel kits. I really like the James Duff parts. They should fit on my frame without too much effort, and I can mount them so that my front axle moves forward a couple of inches. The important thing for this swap is that you either need to use a ford front axle or add the radius arm mount to your current axle.
    The new coilover kit from SkyJacker looks promising but I haven't researched that too much yet.
    I have some links you might like, but they are on my PC at home...

    DougP
     
  3. Chaz88K5

    Chaz88K5 1/2 ton status

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    with the ford set up you can make the radius arms wristed so you really wouldent lose all that much flex..go check out www.bcbronco.com there is a set of radius arms on there..they look bad ass
     
  4. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    Some more thoughts after spending time designing the suspension in an excel speedsheet.

    First the goal of this suspension would only be 4-5 inches of lift and moving the front axle foward 1-1.5 inches. I need to meassure how long of shock I can fit vertically and still achieve this lift height with out the shock coming through the hood (no body lift). If I can use a shock with 12 inches of travel mounted vertically with 38 inch radius arms, the castor angle would change about 18 degrees through the travel. This seems pretty bad to me but this is what many long travel ford suspensions do. I don't think street preformance woudl be too bad because of the limited movement of the suspension on the street. How bad would it be off-road? I don't know. Also once the truck is in 4 wheel drive the forces on the front axle that are affected by the castor angle totally change. I found information on caster angle setups for rear vs front wheel drive but nothing about 4-wheel drive. I don't think using fords radius arm mounts would save that much money over heim joints and the heim joints are far superior. I now understand why poeple use a linked system. Thanks for listening.

    Later
    Mike
     
  5. m j

    m j 1/2 ton status

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    a 3 link would be much better choice
    unless you like the idea of cutting up a dif to install C bushing mounts
    seems like a lot of work to get something that binds
    a 3 link is the most limber suspension you can stuff under you
     
  6. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    The problem with radius arms is that by design, they CANNOT articulate. Ideally you should be able to use a heim joint at every suspension mounting point and the suspension would still work, meaning bushing compliance isn't a big factor. With the radius arm, the only twist available is bushing compliance, a model with solid joints holding it all together would not articulate at all. That's where the 3 link shines, it moves freely with rigid joints. Technically if a radius arm suspension is to move freely, it would try to twist the axle tubes relative to each other. Build a little model with some wood or wire or something and you'll see that radius arms cannot articulate in theory. The can move straight up and down with no problems, just can't articulate.

    Now, here in the real world, we've all seen broncos with radius arms that flex reasonably well. The key is long radius arms. The longer they are the less castor change through the wheel travel and the less the bushings have to deform to allow articulation.
    On a street/offroad rig, the majority of your suspension motion is going to be straight up and down which is fine, and with extended radius arms you'll get decent articulation for offroad use. And like you say, it's less problem to keep joints in and to package in the truck.
    Look at some rovers, they use radius arms up front with the same problems as the fords, but they use a different attaching method that you may want to consider.
     

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