by Steven Jay Bernstein, BMWCCA
I replaced the rotors and pads with the OEM stuff you suggested. It's only 5k later, and they're warped again. Why??
This is a sign that you didn't find the root cause of the problem. Yet. Assuming that they warped in less than 1 year and you got them from a dealer, the rotors are under warranty. You can replace them for free. But you have to examine the other components in the suspension, one by one. Clearly, one must examine each bushing, each tie-rod assembly, and the shocks. Bushings should be checked for hairline cracks; specifically look at the lower control arm bushings and thrust arm bushings. These can be disconnected in order to examine them. Tie-rod assemblies, track rod, and idler arm (in the E28) should be checked for play, and can be checked by hand. Ball joints (in lower control arm or thrust arm) can be checked by the bar-under-the-wheel test, usually, and should also be checked for visible signs of boot deterioration. Shock diagnosis is difficult, since the "bounce-test" is useless. Often, the type of driving and mileage must be considered, as well as how tires wear, how well the car tracks at high speed, and how much the car leans on cornering. My first E28 lasted with shocks until 150k, my newer one seems to need them after only 80k. Finally, a four-wheel alignment should be performed so that the rear wheel alignment can be measured (there are no adjustments here) and the front wheel alignment can be measured and adjusted. In my older E28, the front strut bearings were a serious culprit, in addition to the shocks. This made sense, since worn-out strut bearings are not able to properly hold the strut in place upon braking, and the result was a couple of BADLY shaking strut assemblies.
One other thing - don't forget that your wheels and tires are also suspension components, and MAJOR ones. I have used both the stock 14" rims and aftermarket 15" rims. Some have used +2 and even +3 sizes. The difference in road feel between 16" and 18" wheels is dramatic, and unless you live in a part of the world with perfectly smooth roads,you may find that larger wheels can exacerbate brake problems. Wheels must not be dented or out-of-round. The same is true for tires. I have seen worn tires make a car feel like it was on its last leg. You may need to purchase new tires to fix brake problems, but that's the subject of another FAQ. Whatever you do, don't be a cheapskate when considering tires. A poor choice may cost you a lot more money down the road.
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