Steering, Bump Steer and Death Wobble
Taking the Wheel: Steering, Bump Steer and Death Wobble
By Justin Banner
If you spent so much on your Jeep’s lift, it’s really disappointing to not match that with a good steering system. However, if you have an older Jeep, you are probably very aware of bump steer and the dreaded “death wobble.” Let’s discuss your Jeeps steering system, how to improve them, and the related conditions that can unfortunately define classic Jeep ownership.
It gets thrown around casually by seasoned Jeep and straight-axle owners, but it inspires fear from the uninitiated. “Death wobble” is a discomforting term and situation, but it’s not as scary and out of control as it sounds. There are also ways to mitigate and nearly end it from ever happening again. To under how, though, we should probably talk about your steering and suspension first.
Terms of Steering
Before we move on, we probably should define a few terms to help explain things later in this article.
Toe is the pointing of the front of the tires as looking at them from above. Toe-in means the front of the tire is pointing towards the center of the Jeep. Toe-out means the front of the tire is pointing towards the outsides of the Jeep.
The wear characteristic of toe-in is the center to the outside tread of the tire is worn in a feather pattern than the center to the inside. The wear characteristic of toe-out is the same, but from the inside of the tire to the center being worn more than the outside to the center.
Camber is the inward lean of the tops of the tires. If they lean towards the inside of the Jeep, this is negative camber. If they lean towards the outside of the Jeep, they have positive camber. The wear pattern is a constant wear pattern towards the center of the tire. Too much negative camber will wear the inside of the tire more while too much positive will wear the outside more.
Caster is the lean of the knuckle at the ball joints as you look at the side of the Jeep. Leaning toward the front bumper is negative caster while leaning back bumper is positive caster. Caster doesn’t have a typical wear pattern but can affect steering effort – especially returning to center after a turn. With positive caster, the weight of the vehicle leading the steering and adds straight line stability and increases natural return-to-center of the wheels but increases steering effort.
With negative caster, the weight is trailing the steering wheels and reduces the feel and natural return-to-center of your steering wheels but makes it easier to turn. Because of this, you typically won’t see more than seven-degrees of positive caster except in vehicles with high-powered steering systems or race cars that take advantage of the weight jacking effects of caster.
That weight jacking happens because the turning wheels change their camber as you turn the steering wheel. When you turn left, the left tire will typically gain positive camber as the right tire typically gains some negative camber. Then it’s vice-versa for the opposite turn. This can put more weight on the outside wheel to improve initial bite into a corner for an asphalt racing car.
Caster is still important in off-road, though, even with our big and heavy wheels. About six-degrees positive caster is the consensus of the experts here, so you’ll get slightly heavier steering but much better straight-line stability. At least in an A-arm vehicle.
It’s All Dynamic, Unless You’re A Straight Axle
With most Jeeps being straight axle, most of these angles won’t change as the suspension moves around. That’s why it’s difficult to make a straight axle vehicle traverse open desert in the same finesse as an independent A-arm rig.
That’s why we’ve seen Casey Currie build 4400-class Ultra4 Jeep as an independent front end rather than keeping it a straight axle. He’s found out the hard way that keeping up with the trophy trucks required a suspension that can change to take advantage of the dynamics of a beaten down desert trail at over 120-MPH and turning in both directions.
The toe, caster, and camber of a straight can change during movement as the control arms pull and push the axle around. However, it will affect both wheels at the same time, giving negative effects as you bound over whoops and turn around corners. Its not that it won’t work, as Ultra4s prove, its just very difficult to make work outside of rock crawling and racing.
One of the first conditions most rookie Jeep owners that lifted their vehicle will meet is bump steer. This is the condition in which the toe angle of a wheel (or both wheels) will change as it travels in bump and droop. How this will change depends on where the steering arm is located on the spindle and the tie rod angle of an A-arm car.
On a straight axle Jeep, it’s either the difference of the drag link’s angle to the trac-bar angle on a standard Jeep suspension or the angle and length of the drag link as it sits at ride height on a four-link or leaf spring straight axle.
Since Jeep has both types of suspensions, we’ll talk each one but the reason they change is the same. By lifting your Jeep you’ve changed the suspension geometry and introduced bump steer. The arc of the control arm, axle, or trac-bar is different enough from the tie rod or drag link to move the tire without your input.
Front A-Arm Suspensions
With an A-arm suspension (WK, WK2, KJ, XK, and KK) the direction the wheel will move depends on where the steering arm is in relation to the spindle’s axle location. If it’s in front of the axle (closer to the front bumper), the tie rod will push the axle to toe-out in bump on a lifted Jeep and toe-in on droop. If the tie rod is behind the axle (closer to the center of the vehicle), it will push the wheel into toe-in on bump and toe-out in droop.
The reason this even happens is because of the angle of the tie-rod is different from the angle of the control arms. The tie rods gain length as you adjust it to straighten out the toe. This increase in length puts it out of phase of the control arms as the angle changes from static to bump and droop.
As the suspension and tie rods move up in bump, the tie rods push outwards as they straighten out with the A-arms. This changes the toe, again toe-in is gained on a tie rod that’s behind the axle and toe-out is gained on one that is in front of the axle. Then its all vice-versa in droop.
The easiest way (by that, we mean little to no fabrication) to correct this is to move the tie rod up with a bump steer correction kit. If you have to custom make one, you’ll have to be sure they have the same taper. Normally, for American vehicles under 1-ton, it’s around 7-degrees or 1.5-in/ft but the A-arm Jeeps use that taper with a 0.590-inch (just 0.00375 under 19/32nds) on the smallest end and 0.750-inch (3/4-inch) on the biggest end.
Just to compare, straight axle Jeep outer tie rods are 0.550- (35/64ths) to 0.558-inch (just 0.0045 under 9/16ths) on the small end and 0.626-inch (about 5/8ths, but 0.005 smaller) on the big end. Chevy “1-ton” taper is 0.68-inch (11/16ths-inch) on the small end and 0.75-inch (3/4) on the big end of the taper. So, while these are all 7-degree tapers, they are all different diameters at their small and big ends.
You’ll need to convert from a standard outer tie rod to a rod end with misalignment spacers. You’ll either have to find a “bump steer stud” with the correct taper and size, get your spindles reamed out to the correct taper of the bump steer stud you’re looking to use, or reamed straight and use a straight stud if something isn't available. These studs will also come with spacers to correct the angle of the tie rods, so they are level with the lower control arm to reduce bump steer. It's also entirely possible that the tie rods would have to be flipped so that they attach to the top of the steering rod of the knuckle/spindle rather than the bottom of it. This will depend on how out of alignment the tie rod angle is when compared to your control arms.
Strut Jeeps (KL, BU, MK49, MK74, and MP/552) will use a similar solution. They will all need to have their outer tie rods flipped and knuckles reamed and sleeved or just straight reamed if using a straight stud. This is so that they sit on the upper half of the knuckle rather than the bottom half, if they originally came that way (the KL Jeep Liberty, for example, already has its tie rods on the top of the knuckle while the BU Jeep Renegade is located on the bottom of knuckle). Since the strut and A-arm Jeeps are very limited on how high they can be lifted, this might not be needed for most lifts. If the lift puts the tie rod at a different angle than the lower control arm, it will need a bump steer kit or have one made.
Front Straight Axle Suspensions
For the front straight axle Jeep that keeps its stock three-link with trac-bar (TJs, JKs, XJs, ZJs, WJs, and the JL), the issue is the change of the arc of the drag link versus the arc of the trac-bar. As the suspension moves up and down, the arcs of both on a stock three-link Jeep will be very close to similar until they reach extreme ends of their movements.
When you lift this type of Jeep, the trac-bar and drag link angles will change and become out of phase with each other, sometimes drastically on taller lifts. The effect is similar in how the tie rods “lengthen” and “shorten” as the suspension travels from bump to droop.
This will affect both wheels, though. So, as the trac-bar keeps the axle located centrally side-to-side, the drag link will push (turning right on bump) or pull (turning left on droop) the passenger knuckle. This also moves the tie rod and turns the left wheel at the same time. If the trac-bar wasn’t there, the axle would move around instead but that would cause major tracking issues as you drive you Jeep normally.
This is how inexperienced YJ Jeep owners eliminate bump steer. While the leaf springs keep the axle mostly straight, it will track wrong and potentially become dangerous to drive on the highway like this. The trac-bar shouldn’t be removed as it can cause a hazardous issue while driving on the road, even on leaf spring front Jeeps.
Triangulated four-link Jeeps will also experience bump steer if the angle of the drag link is too high. The triangulation of the upper links will keep the axle located centrally in place of the trac-bar. However, if the angle of the drag link is too much, it will “lengthen” and “shorten” as the axle travels.
Solution to Bump Steer
The common solution for all of them is to install a pitman arm that drops lower than the stock one. This will help place the drag link equal to the trac-bar on three-link Jeeps and reduce the angle of the drag link angle. An additional solution for the trac-bar is to get a kit that drops the mounting location on the chassis or raises the mounting location on the axle (or both), as this will bring the trac-bar angle into sync with the drag link.
If a pitman arm isn’t enough of a solution, a high-steering kit would be another solution, which is usually a new steering knuckle for the passenger side. This moves the mount for the drag link up and, again, reduces the drag link’s angle. TJs, ZJs and XJs can use a WJ passenger knuckle to raise the height of the drag link without resorting to an expensive, custom made steering knuckle.
Another phenomenon of lifted Jeeps and older ones with damaged or worn loose suspension and steering components is “death wobble.” If you’ve never seen or experienced it, it can be an eye opening and potentially dangerous situation. Owners that aren’t knowledgeable about it may let the steering wheel go because they won’t understand what’s going on and panic. Those that are know that you must hold on to the wheel and reduce speed until it stops, or you come to a complete stand still.
What’s occurring is that the motion from a wheel out of balance, a bump in the road, groove, or even hitting the brakes that causes the wheels to move. This becomes a full oscillation as each part of the solid axle’s suspension and steering systems fight against each other instead of absorbing it.
Some compare this to ripples in a pond, “As your Jeep drives down the road it vibrates. Imagine the vibration is a ripple in a pond, starting at the front bumper and traveling through the Jeep to the rear bumper, then bouncing back. In the case of your Jeep the ripple in the pond is a constant and ever-changing wave,” said Mike Gardner of Throwing Wrenches said to Quadratec in March of 2018.
Driving Through It
If you experience death wobble, the most important thing to do is to not panic. The moment you panic, you lose control in any situation you run into with your Jeep. You want to maintain grip on your steering wheel, but don’t go “white knuckle” and grip as hard as you can. You can end up injuring yourself if you do.
As you sustain your hold on the steering wheel, steadily bring your Jeep down in speed. Don’t slam on the brakes, don’t mash and release – apply constant and steady pressure to slow it down.
Speeding up to make up for a braking mistake won’t work, either, and will most likely make things worse. Despite the wobbling, you can still steer your Jeep, too. So, as you’re slowing down, allow traffic to pass and make your way safely to the side of the road. If you’re on a back road, just slow down as steadily as possible and ignore the jerk honking their horn behind you.
Fixing Death Wobble
First, let’s address what won’t fix death wobble: a stronger steering stabilizer. If you install one of those, you’ll end up either masking the issue (not good) or making it worse. It’s not a bad idea to have a steering stabilizer, but it’s not a promising idea to get it because of death wobble.
Also, just because your new JL is factory fresh, it could also potentially experience it. It’s not a lift or age issue but an issue that is just part of ownership of a solid front axle vehicle. There is a TSB out over it right now, but not a fix because there are a number of things that can cause it.
The first thing to do is check the bushings or rod ends of your Jeep’s control arms, steering components, and trac-bar. Also check for any loose nuts and bolts and check the ball joints for proper grease filling or if there is any damage to their dust boots. If any of those allow too much movement, this can cause the wobble.
Loose or bad wheel bearings will cause wobble. Modern Jeeps use hub unit bearings, so you really can’t maintain them. If you own a Jeep made before 1984 (or any Jeep prior to the YJ), you can repack the wheel bearings as part of its normal maintenance, but you’ll also want to inspect them for damage or wear before you do that.
Bent parts can also cause death wobble, so make sure the parts are straight or are in line with how they look stock. Even if your control arms aren’t stock, check for cracks and abnormal bends. Check the balance of your wheels and tires as well as checking the alignment as the vibrations caused by those issues will get death wobble started and may make things worse.
If you’ve just installed a new lift kit, try loosening the control arms and track bars then shaking the Jeep around. It’s possible that they didn’t get a chance to settle as you were installing your kit, so loosening, shaking, and then retorquing them back to specifications might help. Once you do that, mark each bolt and nut to their control arm or mount with a high-visibility marking.
This will allow you to see if any of them had moved and potentially loosened up before anything happens. Also, if you haven’t realigned your Jeep after lifting it, you need to do that. Again, the lift will have changed the suspension angles and that will cause issues like death wobble.
It All Probably Sounds Very Complicated
If any of this has you worried about lifting your Jeep, relax. A large majority of these issues will have been thought about and eliminated or reduced in a full kit designed for your rig. Most kits will have a solution included in the kit. At the very least the manufacturer will offer a solution if your kit didn’t come with one.
Death wobble, however, is simpler than it sounds. Most of the issues stems from loose, misaligned, or broken parts. However, it’s not a simple as throwing on a steering stabilizer and calling it a day. Old Jeeps will potentially exhibit wobble more often, the condition is inherent to all straight axle vehicles.
This includes the last JKs and the new JLs. It will be less likely because their parts will not be worn out, but if you lift those new Jeeps without allowing them to settle before torqueing the arms to spec and realignment the suspension, you’re going to get the wobble.
So long as you stay calm, work though them, both bump steer and death wobble can be driven through and reduced or repaired. Vicious Off-Road offers solutions from the top aftermarket Jeep manufacturers. This means you have your one-stop shop for improving the driving of your Jeep.