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12-14-04, 02:28 PM
My new Specialized came with Avid BB-5 disc brakes and the front has been a problem since day one. The brakes stop well when applied with force, but under light braking the front seems to 'pulse'. With the bike in a stand, I spun the wheel and slowly squeezed the brake lever. At a certain point, I got a rhythmic scraping noise. Scrape...scrape...scrape...(thanks Koffee) went the brakes, and always at the same point in the rotation of the wheel.
Looking at the small gap between the pads and the rotors, I can see a very slight (perhabs 1mm or less) side to side movement. That is, the light I can see between the pad and the rotor disappears at the spot in the wheels rotation that coincides with the pulsing sensation.
The mechanic at my lbs first tried addressing this situation by re-torquing the bolts on the rotor. This did not work. He tried scuffing the pads with an abrasive, and cleaning the brakes with a solvent. This did not work. He also re-torqued the brake calipers. No help there. He then replaced the front rotor and pads, cleaned and retorqued all parts of the front brake system. The problem persisted.
Today, he installed a new front wheel with a different hub, going from a Deore to a Nexave C501. All parts were cleaned and torqued with a torque wrench. He re-used the second (replacement) rotor and, I believe, the skewer from the deore hub. I am NOT positive about the skewer being reused. The problem is the same as before. The side to side wobble of the disc, while small, persists, as does the 'pulse' sensation, which is most noticable under moderate to light braking at slow speeds, but is present at all speeds. This occurs with the suspension fork either active or locked out.
I have no idea where to go from here. Any help would be most appriciated.
Thanks!
Looking at the small gap between the pads and the rotors, I can see a very slight (perhabs 1mm or less) side to side movement. That is, the light I can see between the pad and the rotor disappears at the spot in the wheels rotation that coincides with the pulsing sensation.
The mechanic at my lbs first tried addressing this situation by re-torquing the bolts on the rotor. This did not work. He tried scuffing the pads with an abrasive, and cleaning the brakes with a solvent. This did not work. He also re-torqued the brake calipers. No help there. He then replaced the front rotor and pads, cleaned and retorqued all parts of the front brake system. The problem persisted.
Today, he installed a new front wheel with a different hub, going from a Deore to a Nexave C501. All parts were cleaned and torqued with a torque wrench. He re-used the second (replacement) rotor and, I believe, the skewer from the deore hub. I am NOT positive about the skewer being reused. The problem is the same as before. The side to side wobble of the disc, while small, persists, as does the 'pulse' sensation, which is most noticable under moderate to light braking at slow speeds, but is present at all speeds. This occurs with the suspension fork either active or locked out.
I have no idea where to go from here. Any help would be most appriciated.
Thanks!