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Death Wobble

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Death Wobble


If you're asking what "Death Wobble" or DW is all about, it is a situation where the front axle begins oscillating with such violence that control of the Jeep is difficult until slowed down, and the entire vehicle shakes to the point you feel it will come apart. Over the years I have heard much discussion about the causes of DW and have come to a conclusion - DW isn't caused by any one factor, but may happen if any of the following are present (not necessarily in this order, either):
  • Poor alignment. The first question I ask these days when someone has handling problems after a lift is whether they had the vehicle aligned. More than half the time, it wasn't. Don't proceed until that's taken care of.

    The front tires will be toed-in following most lifts, especially on the LJ, MJ, TJ, XJ, and ZJ because of the steering arrangement. When you hit a bump on only one side of the axle the tire will begin to bob up and down. Since the Control Arms are no longer horizontal, they will pull that side of the axle farther back as it goes down - this will turn the wheels slightly to that side. Once the tires pull to that side, the 'scuff' of the vehicle traveling straight ahead will slow the tire and begin the same process once again.

    Drop Brackets can also help reduce this, since they bring the control arms back to a more horizontal position. Sometimes this can be caused by excessive toe-in of the front wheels-think of it as the tires being cross-eyed and not knowing which tire is dominant

  • Loose or worn Trackbar mount. The trackbar prevents (or reduces) side-to-side motion from the four-link front suspension on the XJ, MJ, TJ and ZJ Jeeps. If the ball joint is worn or the trackbar mount is loose, it can allow lateral wobble as described above
  • Trackbar, Pt II. The trackbar mount at the axle end can loosen up or 'egg' the hole and cause a lateral wobble or wiggle.
  • Poor Alignment (Part II). Lifting the Jeep involves changing the caster of the axle. If the stock control arms are used, the pinion will start pointing down, away from the t-case output shaft. As it points down, it changes the caster of the axle and therefore throws off the self-centering engineered into the axle. Remedy this by using adjustable control arms.
    • These figures are according to '94 factory manual except where noted. (may vary for 2000+ low-pinion axles and pre-91 disconnect axles).
    • Camber (not adjustable) = 0 degrees (+1/2 to -3/4 acceptable)
    • Caster = Manual tranny +6.5 degrees, auto tranny +8 degrees (5 to 9 acceptable)
    • Toe-in. Depending on the year of your Cherokee, toe settings will vary.
      • 87-94 you want 0" inches, + or - 1/16
      • on 95-96 you want 0" +1/8 or - 3/32
      • on 97-98 it's 0" +1/4 or -3/32
      • on 99-2001 its 1/8" +3/32 or - 1/8
  • Unbalanced tires. Once again, as they start throwing the axle around, the only way to stop it is going to be by slowing down.
  • Steering Stabilizer. A tight steering stabilizer can mask problems with the steering, but if it's loose it may allow DW to occur in cases where it normally wouldn't have.
  • Ball joints. Worn ball joints are a danger anyway as they may fail and cause uncontrollable steering loss, but by allowing the wheel to move laterally and independently of the opposite wheel they can also contribute to DW.

This page used to have a table showing typical control arm lengths. This has been moved to the RE Drop Bracket page.

A fellow Jeeper hit the nail on the head with his comments about DW. Tom's been around 4x4s forever, and has an engineering background that makes him make sense.
  DW's are caused by a rather simple problem, but one that can be hard
to track down. Your suspension system (which includes the body) is
out of equilibrium. Energy is being temporarily stored somewhere and
then released, and the cycle repeated. Energy storage can be in many
different areas. It can be in the sidewalls of the tires flexing, or
the rubber in the bushings of the springs and control arms, or in the
springs, or even in the flex of the body. The energy being stored is
caused by something being loose in the system, such as ball joints,
tie rods, control arm bushings, leaf spring bushings, motor mounts,
etc. or something out of alignment.

What makes things tricky is that you can have all of these problems
and have no DW. It has to do with the rate at which the energy is
stored and released. If the storage and release rates are close to
the same, you are in for trouble. That is why changing tires many
times will kill DW. The new tires are stiffer or softer than the old
ones and as such store and release the energy at a different rate.
The purpose of a steering damper is to change the rate of storage and
release of the energy, just as are your shocks.

I say all of this to point out that you can have all of the equipment
working correctly and still have DW, but in most cases I have seen,
there is a defective component that you haven't found yet. My first
rule of thumb is to check all the rubber parts first. They fail the
quickest and store/release the most energy. Second is to look for
loose connections/connectors such as tie rod ends. Third is to get
out a tape measure and check that you have approx .125" of toe in
(difference in the distances between the front edge of the front of
the tires and the rear edge of the tires. After that I check the
caster. Lack of caster leads to a unstable system.

If all else fails, you need to retune the system. Start with a new
stabilizer if it is old or go to poly CA bushings.

-Tom "Old Man" Houston

e-mail Jim
created: August 29, 2003