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This is a common symptom when the brake rotors in the front are warped from overheating of the brakes, worn brakes, or worn brake rotors. The first step to take is to have the front rotors measured to see if they have enough material to machine, if so and the brake pads are not worn...the rotors shoud be machined true and brakes reassembed. If the rotors are worn, it would be best to have a complete brake job performed to complete the repair.
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BMW Factory Training, ASE Master Techinician, Advanced engine performance.