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Correcting Bump Steer Stock verses dropped pitman arm

#1 User is offline   Tom 

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  Posted 04 March 2004 - 10:42 AM

This is my understanding of bump steer and some of what causes it and how we fixed our TJ.

With Jeep TJ suspension, the track bar locates the axle laterally, and that bar operates in an arc, the drag link (steering link, tie-rod to pitman arm) also operates in an arc. So, with the TJ, what you really want is making the track bar and drag link angles parallel to each other. This way, the horizontal movement of the drag link will be virtually identical to the axle's movement, which means that there is no steering input (i.e.: bump steer).

After installing the RE 4.5 LA, the drop pitman arm was installed. There was some bump steer after that but it was not bad. months later we removed the drop pitman arm and installed the stock arm. This allowed the track bar and drag link to be closer to parallel. This almost eliminated the bump steer.

Then we moved the axle track bar bracket from the bottom front of the axle to the top front of the axle. Moving the track bar bracket to the top front of the axle moves it away from everything else (no rubbing) and made it almost straight and a stronger track bar. A little shorter as it did not need the bend in it to reach the old bracket. After the track bar was moved, the drop pitman arm had to be reinstalled. This allowed the Track bar and drag link to be parallel in fact almost one behind the other in line. The Jeep has no bump steer, you do not feel every bump, hole etc. in the road through the steering wheel like it use to.

So the use of stock or dropped pitman arms all depend on which one gets the track bar and drag link closest to parallel.

If the track bar is at say 20 degrees and the drag link is at 30 degrees then as the axle moves up and down the difference in the arc travel of the two bars will be felt in the steering wheel. Both bars are attached to the axle at one end, and to different points at the other end i.e. frame and steering gear box. It the bars are not moving the same, the frame is not going to move so you feel it in through the steering gear box/wheel.

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#2 User is offline   Jim B 

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  Posted 04 March 2004 - 02:22 PM

Tom,

Great write up. :amazed: We are going to have to pull our resources and get you a 2 mp digital camera. :rolleyes: I would love to see your reposition track bar bracket at the axle.

A good while back when I had my 4.5 I don't remember having a drop pitman arm, I believe I used the stock. Where I have seen people having the bump steer is that the axle bracket hole get's worn out, as soon as you hit a bump the trackbar shifts back and forth causing the bump steer.

The Geometry as you stated seems to be the major cause that drivers, manufacturers sometimes neglect to pay attention to. Others bump steer problems include, bent drag link, bent tie rods, worn out ball joints, etc.
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#3 User is offline   JeepinIan 

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Posted 04 March 2004 - 10:29 PM

Bump steer in leaf sprung vehicles is due to the angle of the drag link as well.
My CJ does not have a trackbar, but the dl is at an angle. This causes the bump steer that I have.
One of the upgrades that I am going to do, when I get all the parts for the upgrade, is to put a high steer on it w/ the tierod behind the axle and dl in front and above te c/l of the axle.
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#4 User is offline   NonStop 

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Posted 22 November 2004 - 02:48 PM

I just pulled one bar and reinstalled a drop bracket I am waiting on an ORGS bar with bushings instead of rod ends. But 1 1/2" molly with a straighter shot sounds better. I have a pitman for 4" sitting around. Any reason this will not work on a wj? looks like there is ample clearance may need inch or two more lift. The reason I ask is that I usually hear/hence think, only of moving the upper mount, guess because it is easier and on need for a new bar

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