brake pedal boing sound feeling?? on 2001 Audi A4 Quattro

My 2001 audi a4 has a strange vibration in the brake pedal when coming to a complete stop. If I slam on the brakes it stops on a dime with little or no vibration, but if I'm coming to a normal complete stop (i.e. at a light or stop sign) the pedal vibrates and continues to depress slightly like the rotors are warped. All rotors in excellent condition, as are the pads. yet this vibration continues and mild . Any ideas?

by in Moreno Valley, CA on February 23, 2010
2 answers
ANSWER by on February 24, 2010
This may be the ABS system activating, and if it is, you may have a dirty wheel speed sensor, or a loose or defective wheel speed sensor. I would advise having an Audi mechanic go for a test drive and see where they think the vibration is coming from.
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ANSWER by on February 24, 2010
bretb sounds right, prob an abs activation. have you had any recent suspension or brake work? early audi abs systems use push in sensors that can back out if cv boots, control arms or work like that is done. sometime rust or dirt can back out a sensor too. if your abs light does not come on after driving a while the sensor is probably ok. also note that a bad wheel bearing can cause the sensor gap to change and uneven tire sizes can also affect activation. audi diagnostic testers and those from vag-com can be used to read all 4 sensors at one time and determine which wheel to start checking first.
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