Is this bump steer or something else?

[mwilk012]

Have you guys considered that there might be nothing wrong at all?

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[KNN]

I spent over a year chasing a similar shimmy down. I’ve (mostly) accepted at this point that’s just just the way it’s gonna ride. Have you tried bouncing the front suspension up and down and seeing if your steering wheel moves? That’s a good way to see if your angles are off and causing bump steer.

 

[bjm00se]

I'm with others who've watched the video and don't see anything out-of-ordinary for our solid-front-axle jeeps.

No, a sports sedan with rack and pinion steering doesn't do that. Different beast entirely.

Yes, if this oscillation increased, it would become death wobble. But it's minor and self limiting.

 

[bjm00se]

As did mine. Even if it is normal, I think it's a design flaw.

It is a design flaw.... well... more like a design characteristic.

I mean, think about the geometry of what happens when our Jeeps hit a bump.

1. The axle pressed up towards the body by the tires hitting the bump.
2. The track bar pivots up.
3. The axle is forced incrementally towards the passenger side by the swing of the fixed-length track bar.
4. At the same time, the drag link also pivots up.
Now, theoretically, the track bar and drag link should be mounted so as to have the exact same hypotenuse geometry. But in the real world, there's always going to be a bit of minor variation since they're different components mounted to differing physical locations. Same reason your alignment has a range of acceptable values, not simply an exact target spec that every vehicle always meets exactly.
5. So any minor variation between the angle and length of the drag link vs the track bar is transmitted via the pitman arm to the steering box and thus the steering wheel.

If you want this symptom gone *completely* I think you're abandoning Solid-Front-Axle entirely and switching over to Independent Front Suspension, which has no need of a track bar, and can set the mount point for the steering rack and tie-rods to be the exact geometric center of the parallelograms in the double-wishbone (or other) suspension configuration.

Everything is tradeoffs. Pay your money, take your chances.

 

[AnnDee4444]

I mean, think about the geometry of what happens when our Jeeps hit a bump.

1. The axle pressed up towards the body by the tires hitting the bump.
2. The track bar pivots up.
3. The axle is forced incrementally towards the passenger side by the swing of the fixed-length track bar.
4. At the same time, the drag link also pivots up.
Now, theoretically, the track bar and drag link should be mounted so as to have the exact same hypotenuse geometry. But in the real world, there's always going to be a bit of minor variation since they're different components mounted to differing physical locations. Same reason your alignment has a range of acceptable values, not simply an exact target spec that every vehicle always meets exactly.
5. So any minor variation between the angle and length of the drag link vs the track bar is transmitted via the pitman arm to the steering box and thus the steering wheel.

*assuming the mounts don't move

 

[bjm00se]

*assuming the mounts don't move

Keep in mind that in this picture, there's exactly one mount that's *deliberately* movable - it's the pitman arm, connected through the steering box to the steering wheel. Everything else is pretty rigid.

 

[AnnDee4444]

Keep in mind that in this picture, there's exactly one mount that's *deliberately* movable - it's the pitman arm, connected through the steering box to the steering wheel.

Which is why I doubt the need to brace the pivot point. I haven't seen any reports of steering boxes with loose sector shafts... makes me doubt that it's really an issue (yet).

Everything else is pretty rigid.

Though not rigid enough in my opinion. If one turn of the drag-link adjuster can rotate the steering wheel X degrees, then even minor deflection of the mount has the same effect... except it immediately springs back in an oscillating manner.

 

[Yondu_JLU]

It is a design flaw.... well... more like a design characteristic.

I mean, think about the geometry of what happens when our Jeeps hit a bump.

1. The axle pressed up towards the body by the tires hitting the bump.
2. The track bar pivots up.
3. The axle is forced incrementally towards the passenger side by the swing of the fixed-length track bar.
4. At the same time, the drag link also pivots up.
Now, theoretically, the track bar and drag link should be mounted so as to have the exact same hypotenuse geometry. But in the real world, there's always going to be a bit of minor variation since they're different components mounted to differing physical locations. Same reason your alignment has a range of acceptable values, not simply an exact target spec that every vehicle always meets exactly.
5. So any minor variation between the angle and length of the drag link vs the track bar is transmitted via the pitman arm to the steering box and thus the steering wheel.

If you want this symptom gone *completely* I think you're abandoning Solid-Front-Axle entirely and switching over to Independent Front Suspension, which has no need of a track bar, and can set the mount point for the steering rack and tie-rods to be the exact geometric center of the parallelograms in the double-wishbone (or other) suspension configuration.

Everything is tradeoffs. Pay your money, take your chances.

Would stiffer shocks help it/ vice versa? I’m running fox 2.0s with resi and they’ve been on the rig for two years and about 30k miles with no service. Have beat on them off-road a few times, and they are longer than recommended for my lift ( 2-3 inch lift, 3.5-4 inch shocks). Maybe I need a shorter shock and potentially softer or stiffer?

 

[bjm00se]

Would stiffer shocks help it/ vice versa? I’m running fox 2.0s with resi and they’ve been on the rig for two years and about 30k miles with no service. Have beat on them off-road a few times, and they are longer than recommended for my lift ( 2-3 inch lift, 3.5-4 inch shocks). Maybe I need a shorter shock and potentially softer or stiffer?

First, don't mistake me for any kind of Jeep fabrication expert. I'm just an enthusiast. I don't claim any kind of mechanic's background.

I haven't driven your Jeep, and I may be misinterpreting. But the amount of wheel displacement in your video looks really minor to me, and I'm not convinced it's more than exists in other Jeeps including mine. So I'm not really sure there's anything more you can do to tune it out.

When you're checking the angle of the track bar and the drag link, make sure you're measuring a straight line between the center of the pivot points, rather than the rod itself, which may show a funny angle due to the bends in it.

Aside from that, look for the usual culprits: play in the ball joints, track bar ends, drag link ends, tie rod ends.

After that, I got nothing sorry.

 

[AnnDee4444]

and they are longer than recommended for my lift ( 2-3 inch lift, 3.5-4 inch shocks). Maybe I need a shorter shock

I would check the bump stop lengths to make sure you aren't bottoming out the shock.

 

[Yondu_JLU]

I would check the bump stop lengths to make sure you aren't bottoming out the shock.

Yeah that’s the only thing I can think of at this point. Maybe I bottomed it out when off-roading at one point and the shock has been getting steadily worse since I’ve continued to drive on it. I do notice a squeaking sound from the front end over speed bumps and a rattle sound over certain potholes on the driver side, but I’ve never been able to pin point it.

 

[Yondu_JLU]

I spent over a year chasing a similar shimmy down. I’ve (mostly) accepted at this point that’s just just the way it’s gonna ride. Have you tried bouncing the front suspension up and down and seeing if your steering wheel moves? That’s a good way to see if your angles are off and causing bump steer.

I tried both with the engine cut on and off and filmed the steering wheel from the inside while doing so. Don’t see even a fraction of a movement from it when pressing down on both sides of my front bumper. The only thing(s) I have not replaced recently are my shocks, which have about 30k miles and have been used off-road. They are longer than needed for my lift (2-3 lift with 3.5-4 shocks). Thinking I may have bottomed out at some point and damaged them and that could be causing the vibration/ jarring movements over more severe bumps.

 

[bjm00se]

I drove a couple hundred miles on the freeway today, and watched my steering wheel with this thread in mind.

Bumps on the highway definitely cause a back-forth movement in my steering wheel, as the jeep continues on straight (so no steering correction is required) much as your video shows.

What I observed is that this phenomenon is much more pronounced if the bump isn't symmetrical; e.g. a filled in pothole or uneven bridge joint, rather than if it's exactly even across the pavement.

My Jeep's certainly done this ever since it was lifted, and probably before that from the time it was new.

Given how the front end is designed, I'm not convinced this is something that can be tuned out or corrected.

 

[Yondu_JLU]

I drove a couple hundred miles on the freeway today, and watched my steering wheel with this thread in mind.

Bumps on the highway definitely cause a back-forth movement in my steering wheel, as the jeep continues on straight (so no steering correction is required) much as your video shows.

What I observed is that this phenomenon is much more pronounced if the bump isn't symmetrical; e.g. a filled in pothole or uneven bridge joint, rather than if it's exactly even across the pavement.

My Jeep's certainly done this ever since it was lifted, and probably before that from the time it was new.

Given how the front end is designed, I'm not convinced this is something that can be tuned out or corrected.

Hmmm well… I’ll have it looked over and see if anything is recommended. If not, it may be time to look at something new in the future — feel like I’m dumping money into this thing only to have it drive worse and worse. I love it but this steering is killing the enjoyment.

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