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What Causes.......

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Tommy, Jul 22, 2000.

  1. Tommy

    Tommy 1/2 ton status

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    What causes the front end to feel like its trying to hop sideways when turning and you hit a slight dip? I have 6" skyjackers, 18/39's. I wondered if its the need for a track bar to keep the frontend in place from side to side movement. I was looking today how I might fabricate this. Has anyone else had this problem, or added this to their rig, and how did you do it?
     
  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: What Causes....hehe the long version

    There are a lot of little things that any combination can cause the hop you describe. The first and most likly in your case your biggest cause is tire/ rim combination. My guess from the size tires your running is you have some offet wheels. This throws off the suspension geometry a great deal. Idealy when you turn the wheels they will pivot dead center the contact patch of the tire. Well with your offset the pivot point is going to be towards the edge of the tire meaning that they are not tracking correctly when they are turned. Remember the axle was designed with a 30 inch tall tire in mind not the 39 your running. This point is determind in the design stage by adjusting the offset angles of the ball joints. They set the pivot point by drawing a line through the axis of the ball joints till the line was in the center of where the tire tread would meet the street. A quick way to verify this is with the truck sitting still on some concrete turn the wheels from lock to lock and then move the truck and look at the mark that was left. Your going to leave a cresent shaped mark where the tire moved instead of a circle. You could play with the wheel offset and get rid of some of this problem and to be quite honest even if you were running a stock size tire to a small exstent some of this would still be there because of the caster angle built into the axle. With a smaller tread width there is less friction developed so it is not very pronouced. This brings us to issue 2.
    Now you probably also had to adjust the pinion angle on the front axle to work with the 6 inch lift. Well this added more caster than the axle was set up for. A good way to get an idea of what I'm saying is to think about a shopping cart with a bent wobbling wheel. When you turn the tires they are trying to wobble like that bent wheel on the cart since the caster is now way more than is needed. Some caster is needed because it helps to keep the truck from wandering but it only needs a few degrees. If it gets excessive the wheels then fight from one side of the axle to the other. In your case, hitting a dip is enough to exceed the traction the tire can handle and you get the "Hop". This can be corrected by cutting off the ends of the axles and rotating them back to the correct angle but that is a job better left to a pro and it's not cheap.
    The hight of the springs is also a factor since they let the axle shift from side to side more. Yes a track bar would help but will not get rid of all the problem without correcting either the caster angle or the wheel offset or possibly both.
    Truthfully you got several things causing the the problem and unless you got deep pockets this may be more of a live with it issue. Fixing the offset would be the easiest. Get a picture on the front axle where you can clearly see the ball joints and where the tires hit the ground. use a straight edge and line it up on the ball joints in the picture and see if you need more or less offset and try to figure out how much. Then you can find some rims with close to the correct offset. That an a track bar may clear it up enough to make you happy.

    Diging it in the dirt with my K5's
    Grim-Reaper
    http://grimsk5s.coloradok5.com/
     

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