Bump-steer Solutions and Causes, written by Kevin from KOR
Cause: The Drag Link and Track Bar on a coil-sprung vehicle are out-of-parallel. (affects some coil-sprung Dodge, Jeep, and Ford models)
Result: You hit a bump, and the steering wheel moves first one direction, then the other direction. The steering wheel will also pull out of your hands when you hit the brakes, sometimes DIVING into the next lane over. Scary stuff!
Solution: You need to make the Track Bar and the Drag Link parallel to each other….but it’s not quite that simple.
Explanation: When a coil-sprung vehicle’s front suspension compresses, like during heavy braking, or over speedbumps, the front axle is forced to move in the arc that the track bar pushes or pulls it in. The track bar is a solid chunk of steel, and it’s not compressing or stretching very far, lol, so the axle moves laterally (left/right) following the arc of the track bar.
From the factory, the Track Bar upper mount and lower mount were more or less parallel with the pavement. When you hit a bump, VERY little side-to-side movement happens, because the TB is nearly parallel with the pavement.
However, when you lift a vehicle, the axle is moved away from the body/chassis. This moves the track bar mounting points further away from each other, and moves the UPPER track bar mount further upward, and as a result, out-of-parallel with the pavement.
As long as the drag link’s (also known as a “steering link” or, incorrectly labeled sometimes as a “tie-rod”…) upper mount is moved *the same* distance upward (typically when installing a lift, both would move the same amount upward) as the upper mount on the track bar, the bars are kept parallel…(though they WILL both need to be lengthened slightly). End result: very little, if any, bumpsteer. All good!
However, old ideas never die…and some folks think that a dropped Pitman arm (the steering arm that the drag link attaches to at one end, and which attaches to the splined shaft on the steering gear at the other end) should be added when lifting EVERY vehicle. On a leaf-sprung vehicle…this makes perfect sense! You WANT the drag link as parallel to the factory setting (parallel with the pavement) because the axle cycles upward and townward following the leaf spring mounts, which is perfectly straight up and down.
However, on a coil-sprung vehicle, the axle follows the arc of the track bar, so adding a drop pitman arm is one of the worst things you can do…because it CREATES bumpsteer! Remember, you want the track bar and the drag link to be nearly parallel. Here’s how you do that…
Tape measure, a print-out of this article, and a pen
What you want to do to resolve bump steer on a coil-sprung vehicle is make the amount of DROP the same amount on both bars. If the drag link drops 4″ from left to right, then the track bar should drop 4” from left to right. Measure from the pavement up to the pivot point of each, and fill in the numbers here:
Lower (Pass. Side) Track Bar mounting bolt to pavement:
Upper (Driver Side) Track Bar mounting bolt to pavement:
Lower (Pass. Side) Tie Rod End CENTER on Drag Link to pavement:
Upper (Driver Side) Tie Rod End CENTER on Drag Link to pavement:
Now, subtract the LOWER measurement from the UPPER measurement for BOTH of the bars. Each bar will have a number between 0″ and 12″. How much are they off? Can you easily make them closer to being the same? Do you need a drop Pitman arm? Do you need a factory Pitman arm? Do you need to relocate one of the track bar mounts upwards or downwards?
Now, even if you get these within an eighth-inch of each other, you’re still going to have the bars moving in a slightly different arc, because typically the drag link is longer (moves in a slower lateral motion through it’s arc) and the track bar is typically shorter (moves in a faster lateral motion through it’s arc). However, you can get lucky and almost feel no bump steer with enough tweaking with it. In an ideal world, both bars would be exactly the same length, but that ain’t reality. You can make up for this by making the track bar SLIGHTLY MORE parallel with the pavement than the drag link is, and as they go through their similar-but-not-same arcs of motion, the track bar will move the axle less laterally the more parallel to the pavement it is.
So, essentially, that’s it. Hope for the best, expect something less than perfection, and tinker with it until you get it as close as you can. Every vehicle is a bit different, and each has it’s own level of difficulty of modification, but with some tweaking, you should be able to get this really close!
This blog post was inspired by Jeremy S., who wrote to us asking how to fix his Bump Steer. If you have a question you can’t get answered elsewhere, e-mail us, and we’ll make YOU a blog post about it, so that others can benefit from the info as well. 🙂