Bumpsteer is driving me crazy

ASSFROW said:

Well if someone tells me they have bump steer I'm not going to be arrogant enough to tell them it can only be specifically caused by one thing. I'm going to understand that they are describing what happens when they hit a bump and start the diagnosis from there. If someone tells you when they hit a bump their JK changes lanes, how would you describe it?

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SoK66 said:

Whose drag link flip / track bar setup did you add? As suggested, are they at the same, or near same angle from the pitman arm to the knuckle, and frame to axle? Are the bushings & TREs OK? Teraflex's approach is a bit differnt, in that they drop the track bar mount at the frame rather than raise at the axle. Not ideal but works fine. (Drag link & track bar are in different planes.) Please advise and we'll see if we can sort this out.

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Well because I didn't expect to get all these replies (thanks for that). I paid extra attention this morning when I was in my JK.

Hitting a bump with my left or right tire will cause a pretty severe shimmy in my steeringwheel. Approx. 1-2 inch turn in the steeringwheel.

When hitting a bump with both wheels simultaneously it also causes a shimmy, but when holding the steering wheel it's nearly noticeable, only when I let go of the steering wheel.

There is a corner in a road over here where I do my death wobble testing. Every time I hit the put hole in that corner (steering left, hitting with right tire) everything start to shimmy pretty bad. I'm sure when I remove my ss, death wobble will occur.

All my components were brandnew added two years ago. The flip kit and teraflex track bar were added a year later. Total miles on axles, lift kit etc. Max. 10.000.

Seems to me you have something worn and not bump steer. Assuming TRe's are fine ?
Sometimes just looking at the front end won't tell the hole story. I would be removing bolts one by one and checking the holes for ovaling. Often missed are the upper CA axle bushings.
You could have a $3000 kit installed and the axle bushings remain stock.
Edit: forgot ... This happened to me and other on the forums. Check your TF track bars turnbuckle. I could not get the turnbuckle to hold tight. I had a small shimmy until one day it got worse. Enough to pull over and look underneath. The turnbuckle was loose. Bolts were both stripped when pulling them out. Trip to tractor supply I picked up 2 grade 8 bolts and finally got the thing to hold.

Have you considered the Gopro idea ?
Filming at 60 FPS you get some awesome slow motion playback.


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sneck said:

so im confused. should the steering wheel move or not as you drive down a road? what is considered normal movement and what isn't?

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Bumpsteer has a limited definition. It sometimes get confused with other conditions.

Bumpsteer is when the steering wheel moves because the arc of the trackbar is different than the arc of the drag link as the entire front suspension compresses or extends.




Because the trackbar attaches to the frame on the driver side on a JK at a downward sloping angle, when the suspension compresses, the front axle travels in the arc of the trackbar out towards the passenger side of the vehicle.

When the suspension extends, the front axle travels the arc of the trackbar in towards the driver side of the vehicle.

If the arc of the drag link is different than the arc of the trackbar and the tires/wheels/knuckles stay in the same vector/direction, the drag link will push or pull the steering even though the tires stay straight due to the different arcs.

If the OP has parallel planes of mounting points for the drag link and the trackbar and they are not at overly steep angles, he doesn't have what is defined as Bumpsteer.

Because he describes conditions of death wobble, if his alignment specs (caster, camber and toe) are within spec, the source(s) of his problems are those that relate to death wobble.

Factory ball joints can fail very quickly if there are other problems going on.

Factory bushings can fail fairly quickly if there are other problems going on and/or if suspension bolts (control arms and trackbars) were not torqued at the new ride height after a suspension install.

For non-flex joint control arm and trackbar ends, all bolts absolutely must be loosened for a suspension install, and no control arm or trackbar bolts should be torqued until the full weight of the vehicle is on the ground at the new ride height, with the bushings in a neutral position.

The rubber Clevite bushings are so soft that if pre-loaded/twisted/binding to a different position than actual ride height, they will fail prematurely. The bushing bolt sleeve will prematurely separate from the rubber bushing. This is especially a problem with the front upper axle side control arm bushings.

Until they fail prematurely, these pre-loaded/twisted/binding rubber bushings that are pinched in between the brackets at the wrong ride height will result in a jittery ride.

The thorough way to inspect the bushings is to (one at a time) remove the control arm or trackbar, inspect for cracking or separation visually, and to insert a long screwdriver or ratchet extension through the bushing bolt sleeve and flex the bushing to inspect visually for separation or cracking under misalignment.

ASSFROW said:

Thanks.

So is it possible that worn out track bar or drag link bushing/end/etc could cause the DL and TB to travel in different arcs, resulting in bump steer?

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They wouldn't travel in different arcs that result in bumpsteer.

However, the looseness in a worn or damaged drag link or tie rod end would provide "jerky" feedback to the steering system faster than the power steering could compensate for when those ends "wobble" or "clunk" due to wandering from the tires hitting road imperfections. This would result in "jerky" feedback through the steering system that could escalate into something that approximates trackbar related death wobble.

Looseness in trackbar bushings or bolts in bracket holes will cause inconsistent steering feedback because when the drag link pushes or pulls against the knuckle, the trackbar is the component that provides resistance. This is why if you unattach the front trackbar and turn the steering wheel, the rig won't turn well and the entire axle shifts from left to right under the vehicle.


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