Most of this post will be focusing on the E46, but the ideas here can be applied to all BMW models. The first thing you have to come to terms with on suspension and BMW is that it costs more to maintain it than a Honda. Think of it this way, a road race car has to have LOTS of stuff done to it to keep it competitive. Your BMW is much closer to a race car than the average Accord. It was designed to run the Autobahn at triple digit speeds and give you the feedback and control you need to be safe. When things wear out, you feel it and you need to fix it. Ever have your steering wheel buck one direction or another under braking? A slight vibration you feel at 80mph but not 81mph? Do you hear clunking when hitting a pot hole? Is your ride just not "crisp" anymore?
Here are some common failure items and the parts I suggest you replace them with:
- Control Arm Bushings: Not a week goes by that someone doesn't ask about this on the forums. Most of the time the symptom is either the steering wheel shaking or jerking under braking, or a clunking noise. The control arm bushing is basically there to provide supoprt to the back end of the control arm itself and on the E46 is one of only three connection points. (see #6 on Diagram) It consists of an aluminum housing, a solid outer bushing pressed into the aluminum, and a rubber lined inner bushing filled with hydraluic fluid. It is a good desing for smoothing out the bumps in the road, but tends to fail within 60k miles and much sooner in colder climates. The rubber cracks, the fluid leaks out, and the bushing becomes much less affective. They are also hard to remove making DIY's more difficult. I personally prefer the solid bushings from Powerflex (no, I don't get spiffs from them). The solid bushings last much longer, give better feedback, last much longer, provide better handling, and are easy to remove for replacement or service to the control arm itself. The cost is a little higher(I got mine for $149 from Bimmerworld.com here) and the only complaint I have heard is that they tend to magnify vibrations caused by other worn suspension components. All that said, they really made a difference on my car, and have withstood some pretty severe abuse now for about 50k miles. If you live where the roads are really, really bad, you may want to stay with OEM style like the Meyle HD's found at places like OEM Bimmer parts here. And contrary to what some say, you do not need to get an alignment if you just replace the bushings. There are positive locator pins that only allow them to mount in a certain place. If your car has more than 60k miles, chances are a fresh set of Control Arm Bushings will make a world of difference.
- Control Arms Assembly: This part of the suspension is also a big part of keeping that tight feel to your car (see #5 in the above diagram). The E46 control arm has an inner ball joint and an outer ball joint. The inner joint connects the arm to the front sub-frame, and the outer joint connects to the tie rod. When these wear all kinds of clunking and vibration are common. Also you might get uneven tire wear and even a feeling of instability at higher speed. The entire arm should be replaced with a quality replacement arm. No shortcuts here, you gotta pony up some $$$ for these. Cheaper versions will fail early and you will have to redo them long before you want to. I prefer the Meyle HD versions found at OEM Bimmer parts here. They are only $350 and worth every penny. If you want a slightly stiffer ride, you can spring for the ZHP versions. I replaced mine with some regular HD versions and found them more than adequate for my aggressive driving style. I had over 139k miles on my OEM arms so replacing these made a HUGE difference in my car. It is worth mentiong that both the arms and the bushings can be done DIY in your own garage. It is not hard and well documented on the net. I have seen Indy's and dealers quote well over $1200 for control arms and bushings, this is pure highway robbery! Borrow some tools and a friend, an afternoon of work can save you $700 or more. Lastly, make sure you get an alignment after doing the control arms. I runied a brand new set of tires by not doing this. More to come, stay tuned......