I own a 2001 BMW 5301. I bought the car new in June of 2001. The car has been fantastic but lately I have been experiencing problems with the brake system. About a year ago I had a problem that started with steering wheel shimming. It would happen after the first 20 mins of drive in the morning right around the same left had turn on the highway. This turned out to be a defective front right caliper. About a month ago, while driving in torrential rains and some tree debri on the road, the brakes felt a bit harder than usual. Drove another ten miles, the ABS, brake and DSC lights came on at the same time and the car started to apply the brakes every so slightly to a dead stop and I could not move the car again. After half an hour while waiting for a tow truck, the brakes cooled down and all the indicators went off. Tried to drive again and in about two minutes the car applied the brakes again. No brake pedal travel after that point. I towed it to the shop and my mechanic told me that the same caliper was defective after 20,000 miles!!! He also told me that the computer indicated that the "ABS pump" was defective and needed to be replaced at a whoping cost of $2,800. After a long discussion, we agreed to replace the defective caliper, all rotors, pads and sensors and wait and see how it behaved. The car is working fine except that when you first take off it makes a squealing sound on the driver side of the engine compartment (like a pump or actuator), the brakes with be very hard the first time you apply them and everything goes back to normal. Is this typical of a bad booster, ASC or DSC unit? Is there such a thing as an ABS pump? I pulled all the diagrams from
RealOEM.com Online BMW Parts Catalog and I don't see an ABS pump. What can I do?
Your help and comments are greatly appreciated.
C. Miletti
cmiletti@nas.edu 
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