Death Wobble is a difficult thing to diagnose and fix, because for it to happen at least two things have to be wrong, but the list of things that can be wrong is quite long.
The primary cause of death wobble is that there is some play in one of the steering/suspension joints. I would say the primary area for concern is probably the trunnion bearing/kingpin/knuckle flange bearing area. On the patrol, there are two bearings on each trunnion. These are taper roller bearings and are located in the top and bottom of the knuckle flange, with four bolts each.
Now it seems as if yours were recently replaced...
With a taper roller bearing, the outer race is pressed into place. If these were not pressed in deep enough, then usage will cause them to become loose. They also need to be shimmed up during assembly, and if this was done incorrectly, this may also cause the problem. Note that the top and bottom shims must be the same thickness.
The only reliable way to check this joint is to jack the front of the car up, place the front axle on axle stands, remove the wheels and split the steering arm ball joints off (drag link and tie rod). Now see how easily the knuckle flange turns. The manual shows that a draw-scale should be used in the hole where the ball joint is fitted, and the resistance should be between 0.6 and 1.75kg. It is best to be as close as possible to the maximum value.
The other area where play may exist, is in one or all of the steering ball joints. While they have been split off, check their condition by feeling how smoothly and easily the taper pin can be moved inside the ball. The movement should be reasonably smooth with a fairly even friction. They should definately not be loose.
The above are the primary causes of the death wobble, but these conditions may exist for a long time before one ever experiences the death wobble, because to actually set up the death wobble, something else needs to be out of spec or out of balance.
This can be one of the following:
1) Bent rims
2) Rims not mounted correctly
3) Out-of balance tires
4) A bump in the road
The best way to check for conditions 1-3 above would be to perform a wheel balancing operation on the car. However, very few people have the necessary machine to do this check. A normal wheel balance should however show conditions 1and 3. To check for condition 2 without the right equipment, firstly make sure the fitting surfaces both on the rim and on the car are clean. Secondly make sure the hole in the centre of the rim fits correctly on the hub spigot. Now bolt the wheels on, and arrange a scribe on the face of the tire. Rotate the wheel, and make sure the line is the same distance from the edge of the tread pattern all the way round. Do the same on the sidewall as well.
- fwa.JPG (32.96 KiB) Viewed 3409 times
Further factors that may axacerbate the death wobble are:
1) Caster angle
2) King pin offset
3) Camber angle
4) Condition of the suspension bushes
5) Steering damper
6) Larger/oversize wheels
The caster and camber on a Patrol are not ordinarily adjustable.
Tha camber angle can only go out of adjustment if the axle tube is bent.
The caster angle is affected by suspension lift. This is normally corrected by using special suspension bushes (caster correction bushes), but can also be altered with drop-boxes or special suspension arms. A reduction in caster, usually caused by a suspension lift without the correct caster correction being used will reduce the stability of the suspension because caster is what causes the steering to self-centralize.
The king pin offset is altered by fitting wider rims, rims with a different offset or wheel spacers. The larger the offset is, the more unstable the suspension becomes.
While the lack of a steering damper cannot cause the death wobble, the steering damper does fight the death wobble and will thus reduce the extent of the death wobble.
Oversize wheels increase the leverage the wheels have over the suspension and steering systems.
Therefore it is important to realize that Tiger Wheel and Tire (and similar service providers) cannot fix the root cause of death wobble, they can only make sure the wheels are correctly balanced. And while this may temporarily remove the wobble, it hasn't actually cured the problem. Note also that the root cause of the problem will also cause other damage in the long run, and must therefore be fixed.
