Bump Steer or something else??
12-19-2015, 12:24 PM
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Bump Steer or something else??
Hey everyone,
I have a 2000 XJ with a 3 in lift. I have a new track bar and steering stabalizer, new shocks all the way around. When I go over bumps, my steering feels loose and my steering wheel jumps all over the place. It feels like something is loose, but I have checked everything my self and took it to two suspension shops. Everything looks tight and to be the right angle. What is the problem?? The shops just say jeeps are loose and jumpy but two of my friends have the same setup and they run tight. Thoughts?? It's driving me crazy
I have a 2000 XJ with a 3 in lift. I have a new track bar and steering stabalizer, new shocks all the way around. When I go over bumps, my steering feels loose and my steering wheel jumps all over the place. It feels like something is loose, but I have checked everything my self and took it to two suspension shops. Everything looks tight and to be the right angle. What is the problem?? The shops just say jeeps are loose and jumpy but two of my friends have the same setup and they run tight. Thoughts?? It's driving me crazy
12-19-2015, 12:49 PM
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12-20-2015, 01:44 PM
#8
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I really almost posted "bump.... Steer." Haha but didn't want to be that guy.
Do you have any thoughts on this?? I'm taking it to a 4x4 shop tomorrow, but don't want to go in blind! I jacked it up yesterday to see about the ball joints and they didn't move, but I have the symptoms. Just want to see if I'm not overlooking something
Do you have any thoughts on this?? I'm taking it to a 4x4 shop tomorrow, but don't want to go in blind! I jacked it up yesterday to see about the ball joints and they didn't move, but I have the symptoms. Just want to see if I'm not overlooking something
12-20-2015, 11:58 PM
#9
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I can't speak on the looseness of the system - that would seem to be play in your steering column, box, linkage, or tie rod ends.
Your steering jumping all over the place going over bumps is definitely bump steer. Since you lifted and are presumably running larger tires, the stock steering stabilizer will not be as effective at damping bump steer. You need a "stiffer" damper.
Why? Let's assume for a second that the XJ steering system is a 1D system. The damping ratio of the system is given by:
ζ = c / [2*sqrt(mk)] where ζ is your system damping ratio, c is your steering damper stiffness, m is the mass of the steering system, and k is the system's spring constant. By running larger tires, you make m larger and thus ζ gets smaller. To keep ζ the same, you have to bump up c...ie make your damper stiffer!
EDIT: This is assuming you properly lifted your rig and that the arcs of travel of your drag link and track bar are nearly parallel through your suspension's travel. If they are not parallel through their travel, you need to fix that before stiffening up your stabilizer.
Your steering jumping all over the place going over bumps is definitely bump steer. Since you lifted and are presumably running larger tires, the stock steering stabilizer will not be as effective at damping bump steer. You need a "stiffer" damper.
Why? Let's assume for a second that the XJ steering system is a 1D system. The damping ratio of the system is given by:
ζ = c / [2*sqrt(mk)] where ζ is your system damping ratio, c is your steering damper stiffness, m is the mass of the steering system, and k is the system's spring constant. By running larger tires, you make m larger and thus ζ gets smaller. To keep ζ the same, you have to bump up c...ie make your damper stiffer!
EDIT: This is assuming you properly lifted your rig and that the arcs of travel of your drag link and track bar are nearly parallel through your suspension's travel. If they are not parallel through their travel, you need to fix that before stiffening up your stabilizer.
Last edited by NM-XJ; 12-21-2015 at 12:08 AM. Reason: Forgot an important point...
12-21-2015, 04:14 AM
#10
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You either have something loose, a bad bushing, or improper geometry. I also have a 3" lift and have no issues running with NO steering stabilizer. I would also recommend swapping tires front to back to make sure the bump isn't setting up some sort of oscillation due to an out-of-balance wheel/tire combo. If that fails to resolve the problem then I would focus your attention on geometry or bits that move when they shouldn't. Best way to check the latter is by having someone turn the wheel (engine running) while you watch everything in the front suspension from the pitman arm to the ball joints. It doesn't take much play to induce a little wobble. Have you checked your caster angle and toe?
12-21-2015, 07:12 AM
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You either have something loose, a bad bushing, or improper geometry. I also have a 3" lift and have no issues running with NO steering stabilizer. I would also recommend swapping tires front to back to make sure the bump isn't setting up some sort of oscillation due to an out-of-balance wheel/tire combo. If that fails to resolve the problem then I would focus your attention on geometry or bits that move when they shouldn't. Best way to check the latter is by having someone turn the wheel (engine running) while you watch everything in the front suspension from the pitman arm to the ball joints. It doesn't take much play to induce a little wobble. Have you checked your caster angle and toe?
I have not checked my toe, and in getting a chirping sound at low speeds, making me think I need another alignment. I just got an alignment which made me think ball joints as to why it got out of alignment.
12-22-2015, 03:38 PM
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So, I've decided to go to a shop and have it re-aligned with toe in and to check my caster and pinion angle. I have the 8.25, so my specs are: pinion caster angle: 6.5 and differential: 84.5 or 5.5 with a 3/16-1/4 in toe in. Anything else I am missing?
12-22-2015, 06:24 PM
#14
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To be clear - bump steer, by definition, has nothing to do with bad ball joints or worn bushings. It has everything to do with poor geometry or improper damping.
The loose feeling in your steering column may very well be related to worn parts, loose parts, etc. So the checks you are doing are good things.
The wheel jumping around when you go over a bump is a different issue entirely. Checking your geometry is a good place to start. Go look at your track bar vs. drag link geometry while you are at it.
The original, stock design of the XJ had some amount of inherent bump steer. That's why those smart engineers in chassis design put a steering stabilizer on it. That and some other minor reasons. So even though a lot of folks here do just fine without one - and I'm not trying to drown out their advice - do not think for one second that there isn't a sound engineering reason to run with a steering stabilizer.
The loose feeling in your steering column may very well be related to worn parts, loose parts, etc. So the checks you are doing are good things.
The wheel jumping around when you go over a bump is a different issue entirely. Checking your geometry is a good place to start. Go look at your track bar vs. drag link geometry while you are at it.
The original, stock design of the XJ had some amount of inherent bump steer. That's why those smart engineers in chassis design put a steering stabilizer on it. That and some other minor reasons. So even though a lot of folks here do just fine without one - and I'm not trying to drown out their advice - do not think for one second that there isn't a sound engineering reason to run with a steering stabilizer.
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12-22-2015, 06:27 PM
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To be clear - bump steer, by definition, has nothing to do with bad ball joints or worn bushings. It has everything to do with poor geometry or improper damping. The loose feeling in your steering column may very well be related to worn parts, loose parts, etc. So the checks you are doing are good things. The wheel jumping around when you go over a bump is a different issue entirely. Checking your geometry is a good place to start. Go look at your track bar vs. drag link geometry while you are at it. The original, stock design of the XJ had some amount of inherent bump steer. That's why those smart engineers in chassis design put a steering stabilizer on it. That and some other minor reasons. So even though a lot of folks here do just fine without one - and I'm not trying to drown out their advice - do not think for one second that there isn't a sound engineering reason to run with a steering stabilizer.
I figured that all of this is a combination of things.