Bump steer but why?

Artsifrtsi

Artsifrtsi

I just wanna go wheeling...
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This post is more of a hope of affirmation/consensus, and not really a what do I do type thread…

In preparation for the JKS 2 inch lift, this summer I refreshed all rubber parts in the suspension and steering. I had a Rusty’s 1 ton steering kit, and replaced it with stock style. Everything was nice ant tight, and the TJ drove like it was new again.

Lift came in, and we installed it. Wheels/tires are 33x12.5x15 Falken Wildpeak at3 load c on 15x8 with 3.5 backspacing. Everything went in smoothly, all torque was applied with Jeep on its own weight, made AL alignment bars, and set toe to 1/8 inch. Castor bolts were set fully forward. Axles centered nicely with the adj TB in front, and TB relocation bracket in rear. Lift did not, and I know better than installing a DPA. Retorqued everything after a tank of gas. The TJ still drive perfectly, can let go of steering without pulls or drifting, does not follow ruts, steering returns to center as it should.

The only “issue” I have, and am sure there is no way to cure, is I have a little bump steer… but only really notices when accelerating or braking. I know this is as the Jeep front lifts or dives, it pushes and pulls the drag link that is now at a steeper angle than stock. my Gladiator (JT) is level lifted 2 inches front, 1 inch rear, and does not do this… either the steering geometry prevents it, or the length masks it…. It it not by any means severe, or dangerous, but only mildly annoying.

here are pics of both… why does TJ do this, and not JT? Is it just the nature of the different systems? Both have about same angle on the DL and TB…


IMG_1854.jpeg


IMG_1855.jpeg
 
@NashvilleTJ please, without talking custom parts, explain how to get a better alignment of the TB vs DL angle. They are both (TJ and JT) almost completely parallel, the basic geometry (disregarding how the tie rod attaches) is very similar on both... The TJ has a couple more degrees on the angle relative to the axle than the JT... is that angle enough to cause the mild (I ONLY notice it in the above situations) bumpsteer I get in the TJ that does not exist on the JT?
 
Artsifrtsi said:
@NashvilleTJ please, without talking custom parts, explain how to get a better alignment of the TB vs DL angle. They are both (TJ and JT) almost completely parallel, the basic geometry (disregarding how the tie rod attaches) is very similar on both... The TJ has a couple more degrees on the angle relative to the axle than the JT... is that angle enough to cause the mild (I ONLY notice it in the above situations) bumpsteer I get in the TJ that does not exist on the JT?
Click to expand...

You mentioned you installed a track bar relocation bracket on the frame side. If you are runing stock mounting locations for the axle side of the track bar, and both sides of the drag link, then your drag link and track bar are no longer parallel. That would definitely cause your bump steer.

Does that make sense?

Edit: I may have misread it. Looks like you said you did the relocation bracket in the rear. But in the picture it looks like there is one in the front.

Edit Again: I see it now, the bottom pic is the JT. Are the track bar locations in the front stock in the TJ?
 
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NashvilleTJ said:
You mentioned you installed a track bar relocation bracket on the frame side. If you are runing stock mounting locations for the axle side of the track bar, and both sides of the drag link, then your drag link and track bar are no longer parallel. That would definitely cause your bump steer.

Does that make sense?

Edit: I may have misread it. Looks like you said you did the relocation bracket in the rear. But in the picture it looks like there is one in the front.

Edit Again: I see it now, the bottom pic is the JT. Are the track bar locations in the front stock in the TJ?
Click to expand...

Yes, stock locations on the TJ. The only change was to bore out the taper to install the JKS TB.
 
It may be the angle of the photo, but here is what you are looking for - ideally the lines from the endpoints/pivot points of the track bar and drag link should be pretty close to parallel. The lines I've drawn are not - but I don't believe a stock TJ setup is perfectly parallel either. It's been a while since I've dealt with a stock TJ steering setup - but it seems like this should be close enough. As I said it also may be the perspective of the photo.

Hopefully someone else will chime in with some feedback, but there is absolutely a way avoid bump steer. Perhaps there is something else going on?


Artsifartsis' Jeep.jpeg
 
Yes, this is all good, and I understand it. Does the JT not act the same way because of the difference in steering type?

I just used measurement software I have, the TJ has a difference of ~1 degree, closing towards the frame. The JT is ~2 degree difference, opening towards frame.
 
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@mrblaine, just wanted you thought on this. It’s not a bad issue, and barely noticeable unless on brakes hard, or quickly accelerating. Normal everyday driving you’d never know it’s there. Is this just something inherent with the stock steering/control arms when TJ is lifted? My Gladiator does not behave this way…
 
First off, I don’t know. But your question as I interpret it “why do different vehicles with similar suspensions/steering behave so differently?” is a good one. I’ve had 3 very different vehicles w/ very similar front suspension/steering designs: ‘97 TJ w/ 4” spring lift, 02 WJ with 1.5” spring lift and ‘08 dodge 3500 w/ 2.5” leveling pucks. All straight axle w/ 4 control arms and a track bar. The TJ and PU are Haltenberger steering and I think the WJ was crossover (@TheBoogieman can you confirm? I sold mine 13 years ago). Anyhow, the WJ was the best driving of the 3, particularly the steering, so maybe its as simple as that. I also think the ultrashort TJ wheelbase amplifies any steering instability issues.
 
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The one interesting thing I saw when comparing, had no reason to inspect before, is the DPA in the JT is leading the steering gear... The gear is almost directly over the axle...
 
NashvilleTJ said:
It may be the angle of the photo, but here is what you are looking for - ideally the lines from the endpoints/pivot points of the track bar and drag link should be pretty close to parallel. The lines I've drawn are not - but I don't believe a stock TJ setup is perfectly parallel either. It's been a while since I've dealt with a stock TJ steering setup - but it seems like this should be close enough. As I said it also may be the perspective of the photo.

Hopefully someone else will chime in with some feedback, but there is absolutely a way avoid bump steer. Perhaps there is something else going on?


View attachment 498915
Click to expand...

Should the drag link line be based on the knuckle joint or the tie rod joint? I always thought of it as going to the knuckle, which would mean the drag link is about 6" longer than the track bar and therefore would require a flatter pitman arm as you increase lift to eliminate bump steer. But maybe the toe change inherent to haltenberger means the line stops at the drag link?
 
freedom_in_4low said:
Should the drag link line be based on the knuckle joint or the tie rod joint? I always thought of it as going to the knuckle, which would mean the drag link is about 6" longer than the track bar and therefore would require a flatter pitman arm as you increase lift to eliminate bump steer. But maybe the toe change inherent to haltenberger means the line stops at the drag link?
Click to expand...

Interesting thought on that. Looks like if the PA were about 3/4 to 1 inch flatter it would put the DL parallel to the TB.

As far as where to measure, I always thought/heard it was to the TRE at the knuckle. If I measure the angles at the TR joint, there's about another degree off of parallel.
 
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The one thing you may "check" is the way the track bar attaches to the frame on the TJ vs the JT. I swapped out to a bolted upper end style track bar (Rough Country Forged) to get rid of the tie rod style end with my 4" lift. I don't have any bump steer related to braking or acceleration. I'm wondering if there is side to side flex with the tie rod style end under braking and acceleration.
 
mjonesjr84 said:
The one thing you may "check" is the way the track bar attaches to the frame on the TJ vs the JT. I swapped out to a bolted upper end style track bar (Rough Country Forged) to get rid of the tie rod style end with my 4" lift. I don't have any bump steer related to braking or acceleration. I'm wondering if there is side to side flex with the tie rod style end under braking and acceleration.
Click to expand...

With the JKS track bar I have in the TJ, the only difference is single vs double shear mounts at the frame (and the JT TB is rubber bushed).
 
Artsifrtsi said:
With the JKS track bar I have in the TJ, the only difference is single vs double shear mounts at the frame (and the JT TB is rubber bushed).
Click to expand...

The JKS would still allow forward and backward movement by the way it mounts and how it is designed (flex joint ball). I think the horizontal (front to back) bolt with the rubber bushing on the JT will limit the forward and backward movement on the acceleration and braking, unlike the JKS mount.
 
freedom_in_4low said:
Should the drag link line be based on the knuckle joint or the tie rod joint? I always thought of it as going to the knuckle, which would mean the drag link is about 6" longer than the track bar and therefore would require a flatter pitman arm as you increase lift to eliminate bump steer. But maybe the toe change inherent to haltenberger means the line stops at the drag link?
Click to expand...

Good eye. You are correct - I was a little too quick on the line drawing. It should be through the TRE at the knuckle. Since it is a solid connection between the pitman arm and the TRE at the knuckle, that connection determines the arc of travel of the steering knuckle as the suspension compresses and droops. To avoid bump steer, this arc of travel needs to closely match the arc of travel of the axle side track bar connection during this movement.

Thanks for the call out.
 
Artsifrtsi said:
@NashvilleTJ please, without talking custom parts, explain how to get a better alignment of the TB vs DL angle. They are both (TJ and JT) almost completely parallel, the basic geometry (disregarding how the tie rod attaches) is very similar on both... The TJ has a couple more degrees on the angle relative to the axle than the JT... is that angle enough to cause the mild (I ONLY notice it in the above situations) bumpsteer I get in the TJ that does not exist on the JT?
Click to expand...

Try tightening the jam nut on the track bar and see what happens.
 
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mrblaine said:
Try tightening the jam nut on the track bar and see what happens.
Click to expand...

Just to chime in, along the lines of this.

From what I'm reading, SOMETHING seems loose or not torqued properly.
Whether that be an axle/frame mount, or jam nuts.

Avoid the headaches of trying one thing at a time, take an hour to crawl under the jeep, and make sure EVERYTHING is torqued to spec.
Control Arms, Tie Rods, Track Bar, etc. Put a torque wrench on every bolt connected to an arm.

I'm betting you find one or two of them loose.
I know you said you tightened everything, but that is a phrase that is thrown around a LOT, and usually remedied by TIGHTENING EVERYTHING.

After that, have someone sit in the jeep and yank the steering wheel left/right to see where/if there is movement, and where the movement is coming from.
 
zachpeakee said:
Just to chime in, along the lines of this.

From what I'm reading, SOMETHING seems loose or not torqued properly.
Whether that be an axle/frame mount, or jam nuts.

Avoid the headaches of trying one thing at a time, take an hour to crawl under the jeep, and make sure EVERYTHING is torqued to spec.
Control Arms, Tie Rods, Track Bar, etc. Put a torque wrench on every bolt connected to an arm.

I'm betting you find one or two of them loose.
I know you said you tightened everything, but that is a phrase that is thrown around a LOT, and usually remedied by TIGHTENING EVERYTHING.

After that, have someone sit in the jeep and yank the steering wheel left/right to see where/if there is movement, and where the movement is coming from.
Click to expand...

Yes, at 10p miles, and at 500 miles after the lift the torque wrench was used on all the fasteners that were touched. At 100 there were a couple, at 500 there were none. I’m going to have to watch that jam nut, this was the third time it was tightened… I’ll check the torque again this weekend.

Is it ok to use lock tight on the jam nut if it loosens again? I don’t imaging a need to adjust it again…
 
Artsifrtsi said:
Yes, at 10p miles, and at 500 miles after the lift the torque wrench was used on all the fasteners that were touched. At 100 there were a couple, at 500 there were none. I’m going to have to watch that jam nut, this was the third time it was tightened… I’ll check the torque again this weekend.

Is it ok to use lock tight on the jam nut if it loosens again? I don’t imaging a need to adjust it again…
Click to expand...

1. How tight are you getting it, and 2. Is the flex joint end centered so it's not bottoming out and twisting when the suspension flexes?

I give mine everything I can with a 24" breaker bar and haven't had that issue, and I use anti seize.
 
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