CJK

Bump steer is caused by the increased angle of the rod that connects the pitman arm on the steering shaft to the knuckle on the passenger's side. Turn the steering wheel, pitman arm turns, link to the knuckle turns the passenger wheel and the tie rod connecting to the driver's side wheel keeps the two wheels pointed in the same direction. The tie rod is parallel to the ground. Compare it to the angle of the rod going to the pitman arm. On a stock suspension the angle is minimal. The higher you lift, the more angle you induce into the connecting rod (drag link I believe is the correct term). Usually a 4" lift will require a dropped pitman arm to reduce the angle and get rid of bumpsteer.

Bumpsteer is most noticable when you hit a bump with the passenger's side causing the suspension to compress. Because the drag link is at an angle the compression acts to effectively lengthen the distance between the knuckle on the suspension and the pitman arm which is attached to the frame. Obviously you are not compressing a rod of fixed length so the increased distance is taken up by the pitman arm moving a bit. That movement is felt at the steering wheel: bumpsteer.

Check your steering linkage to see if AEV replaced the stock pitman arm with a dropped version. I believe their standard suspension upgrade is only 2-3" which is usually not enough to require a dropped pitman arm so they may not have installed one on your 4" lift. A dropped pitman arm will lower the upper end of the drag link and get it closer to parallel with the tie rod and should cure your problem.

kntr

AEV installed a 4" Superlift. This is the one they recommended.

rubimonster

I have the superlift 4" also and have some bumpsteer. All the research I've done on this site leads me to believe a dropped pitman arm will do the trick. Also read that new contol arms (specifically uppers) are needed. I'm going to be buying the new pitman arm from skyjacker and the superlift steering stabalizer before I dish out all the cash for new control arms.

On a side note... have you had yours off-road yet with the 37" tires. Any rubbing issues. I took mine on a decent trail and it looked to me that with 37" tires I'd have some rubbin issues...but love the look

RMEF_lifer

With the 5 link front ends of JKs (TJs, XJs, Dodge Rams, etc.), the other critical issue that nobody has yet mentioned is that the pan-hard rod (track bar) and the drag-link need to be parallel and travel through similar arcs. If this is not the case, you will get bumpsteer.

If the suspension uses a drop pitman arm, you need to use a dropped track bar bracket on the frame end.

nukeman

This is also one of the leading causes of death wobble.

kntr

So drop pitman and adjustable uppers?

CJK

RMEF makes a good point about the geometry of the track bar and drag link. Hadn't thought about that.

Adjustable control arms allow for fine tuning the angle of the axle and adjusting camber/caster (I forget which). Allignment shop can tell you if you need them.

What did AEV and/or Superlift suggest?

RMEF_lifer

The adjustable control arms allow you to adjust caster, pinion angle, wheelbase, and thrust angle. Your suggestion to yo back and see what AEV / Superlift recommend is the best thing.

One thing I will add on drag link / track bar geometry. These need to travel through the same arc to prevent bumpsteer. With the design of the JK, it is technically impossible to eliminate bumpsteer, but it should be able to be minimized to the point it is almost unnoticeable. The more lift you add, bumpsteer increases unless you redesign the track bar and/or drag link. There are great books on chassis engineering that will explain all this stuff in excruciating detail that make for great insomnia medicine.

Back to my cave at work .....

kntr

Ill make some calls today. This is really bothering me. I wanted a Currie lift and I was told the Superlift was a great lift and I would have any problems. I guess I shouldnt have let them talk me into it.

CJK

AEV and Superlift are both quality outfits, I'm sure they'll work it out for you. I know it's frustrating but sometimes even with highly engineered kits it takes some adjustment to get all the kinks out. One thing to keep in mind: your springs will likely settle a bit after a break-in period so don't be surprised if they get it all dialed in and then you have to adjust it again after a few months.