Steering wobble/shimmy, poly bushes, ball joints and a FIX

[Laurence]

First off, apologies for the long post, but I thought I’d share my recent experiences of various front suspension issues. Having gained so much knowledge and information from this site I wanted to put this thread together in the hope that I can assist others when trying to diagnose various problems they have.
I have put the problems that I have faced in chronological order so you can see what the issues were.
So, here’s the back ground. I have a 2002 3.0 diesel sport that I have owned from 34000 miles. It has now covered 118000 (and before any one asks, no I haven’t changed the transmission fluid!).


Problem 1. Excessive tyre wear on the front outside edge
This was an odd one as usually tyres wear on the inside edge when the tracking is out. As a first check I had the tracking done but this was near enough in spec.
The next stage was to work out why the tyre wear was so bad. Having looked at the X5’s suspension set up and read several threads, everything was pointing towards the Tension Strut bush. Having looked at the bush it was showing some visible signs of wear (to be expected with the mileage) but no serious cracking to the rubber or oil loss. However, if I held the front wheel at “10 to 2” position and rocked it, I could see a fair bit of movement in the Tension Strut bush.
So, looking at the geometry of the front suspension, the Tension Strut bush takes a fair amount of punishment when cornering; due to the forces involved, a worn bush would induce more –ve camber when cornering and cause greater outer edge tyre wear. (Note: any amount of high speed corning will cause rapid outer edge wear on the front tyres, you would have to decide what was “normal” wear”)
Fix. So, replacement of the Tension Strut bush was required.
Usually when I replace parts on a car I like to “upgrade” where I can. I decided to go for a Super Pro poly bush. Now, I have read lots of opinions about the benefits and drawbacks of poly bushes, so I made this decision with all this information to hand. (note, I also changed the wish bone bushes but with standard BMW rubber).
The installation of the poly bush transformed the car. The ride was a little harder but the corning capabilities and general “feel” of the car was transformational – but it immediately created another problem, steering wobble or shimmy.

Problem 2. Steering shimmy
The installation of the poly bushes tightened up the front end of the car significantly but I was left with a steering wobble or shimmy at 65 – 70mph.
It would appear that the worn Tension Strut bush had masked other problems with the front suspension. The vibrations I was now experiencing were not present before the bush change.
Fix 1. The first and most obvious fix was to get the front wheels balanced. This made a slight improvement, but the shimmy reappeared.
Fix 2. Having read a few more threads about shimmy problems one area that I hadn’t checked was the ball joints. A comment that Weasel had made on another thread was that a failing wishbone ball joints can cause steering wobble/shimmy. So, rather than just check the ball joints, I ordered up new tie rod ends and wish bones.
Nearly all of the ball joints that I replaced were loose, but none felt excessively worn. However, I do realise that the performance of ball joints under load can be very different.
Having replaced these items the shimmy had almost gone, but not completely.

Fix 3. My last area of investigation was the tyres. Given all the problems I had experienced above, the front tyres, although balanced, did not appear to have worn evenly – the wear around the circumference was not even. So, I bit the bullet and replaced the set and all the shimmy/wobble has finally completely gone!!

Now, I can’t put my hand on heart and say what caused which part to fail first, but it was probably a combination of general wear that should be expected at the mileage I’ve now done. So, hopefully, that should be the end of my shimmy/shaking for a few more mile to come.