Help a Newb with JKU Bump Steer

jerzsubbie

New Member
Joined
Sep 5, 2020
Location
Davidson
This is my first solid front axle vehicle, just bought it 3 days ago, but have done about 350 highway miles already and noticed some uneasiness after hitting bumps or expansion joints. I've googled quite a bit and am pretty sure this is bump steer and i *think* I know why, but am not 100% sure.

Vehicle:
15 JKU 64k mi, 3rd owner
3.5" RC 2.1 lift with drop brackets & cam bolts (I know... dealer installed before 2nd owner purchased)
OEM track bar w/ RC riser at the axle side
OEM drag link w/ OEM pitman arm
RC dual stabilizer

The worst case was yesterday on my way back from Mebane, on I85. I was driving 75 on cruise control, hit a bump at the end of a small overpass, the wheel wiggled back and forth, cruise control abruptly cancelled, and traction control kicked in. It scared the heck out of me for a half second until I realized what had happened.

I grabbed an angle finder and got the following measurements:
Pinion angle - 1*
Caster - Driver 4.1*, Passenger 6.7*
Track bar (measured at bolt centers) - 3.9*
Drag link (measured at ball joint centers) - 6.5*
Clearly these two aren't parallel, but how much wiggle room do you really have?
Speaking of wiggle, without jacking it up, I didn’t notice any wiggle in any of the linkage joints on the front axle. Couldn’t really talk about the knuckle ball joints.

What would you guys recommend I try first to fix this? I'm guessing play with the cam bolts to get the caster to about 4.5* on both sides? Do I need to get something like the JKS drag bar flip with track bar bracket? I am likely going to rip out the suspension and replace it with something of much nicer quality, but want to at least get this driving better in the near term.

Take it easy on me, please :)
 
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Shimmy in the steering after a jolt like that is 99.99999% Track Bar related. Ask me how I know lol. A quick google says factory castor is 4*. Check the adapter bracket at the TB or, better yet, shit can the bracket and stock TB for a quality adjustable piece.
 
Thanks. That was the first thing I began looking at but other than “track bar and drag link should be parallel”, I couldn’t find much info on helping my diagnose. The fact that mine aren’t parallel and the track bar has been raised while the track bar is stock on both ends has me *this* close to buying a JKS drag link flip & track bar bracket to get both adjusted evenly.

I’m leaning towards a 3.5” RK lift which comes with a beefy track bar so I’m on the fence on buying that separately.
 
That RC lift should have a drop pitman am coupled with the track bar bracket to reset geometry. You'll either need that pitman arm, an adjustable track bar (in stock hole), or a drag link flip. I'm not very versed on JK stuff but I'd likely go with the drag link flip.
 
Flip that drag link. That will aid in correcting bumpsteer. You may need an adjustable TB anyhow, just to properly align.
Also, adjust that caster. That's a serious difference from right to left.
 
Welcome to our little home on the web.
Some good dudes here.
The sophisticated gentleman peddling his carbon powered bicycle in crocs above me is one of the more well respected Jeep fools anywhere.
He dont know anything about good eating, but he knows Jeeps and how to find suga mommas. I'd trust him.
 
Ron said:
Welcome to our little home on the web.
Some good dudes here.
The sophisticated gentleman peddling his carbon powered bicycle in crocs above me is one of the more well respected Jeep fools anywhere.
He dont know anything about good eating, but he knows Jeeps and how to find suga mommas. I'd trust him.
Click to expand...
I had noticed him referenced in other threads numerous times, while lurking the past couple weeks, but that's good to hear the confirmation because I just placed a couple orders.

JKS drag link flip kit
RK adj track bar
Teraflex OEM style steering stabilizer (replace dual RC kit once I fix the bump steer)
and a few other odds and ends

Thanks for the help, and encouragement to spend a little money :)
 
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Ron said:
Welcome to our little home on the web.
Some good dudes here.
The sophisticated gentleman peddling his carbon powered bicycle in crocs above me is one of the more well respected Jeep fools anywhere.
He dont know anything about good eating, but he knows Jeeps and how to find suga mommas. I'd trust him.
Click to expand...

Thanks for the kind words. But...
I actually have 2 carbon bikes now. You gotta keep up, man.
 
I was able to adjust the F LCA cam bolts to get my caster at 3.7* and 4.2*, figured that’s close enough for now, but it hasn’t really effected how it drives.

Well... I decided to just pull the trigger on replacing the entire RC lift and doing everything the way I want to.

RK 3.5” springs
5100’s
MetalCloak Front Lowers
MetalCloak QD sway bar end links
MetalCloak adj Track Bar
JKS drag link flip w track bar bracket
Synergy stabilizer clamp
Teraflex stabilizer (flipped)
Taller front bump stop spacers
**Order mix up and now I also have an extra RK track bar, probably gonna just sell it

It’ll probably be a couple weeks until I get to doing the install but I’m excited. Hopefully I can find some time to do the drag link flip one evening this week.
 
I don't know what you are measuring but on a solid axle vehicle where the inner C's are appropriately (and identically) installed the caster is the same on both sides. If it was that far off you would have a cross-caster alignment issue and the vehicle would want to pull to to the left (based on both your sets of numbers). What are you measuring?

Also, check your wheel bearings. You did not post your tire size but with that much lift I assume 35s? Depending on the wheel offset it is probably putting a significant amount of extra strain on the crappy unit bearings all these newer vehicles use.
 
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