Bicycle Mechanics - What's going with these brake pads?

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.



PDA
Airburst
10-28-10, 05:50 AM
I recently acquired a mid-1980s Saracen MTB, equipped with cantilever brakes. I tested it out for the first time yesterday, and the front brake made a scraping noise every time I applied it. The brake pads are fairly new, but on close inspection, they seemed to have bits of metal stuck in them. I picked at the bits with a pin, and they came out fairly easily, leaving pits in the rubber. The metal didn't come out as large pieces, it sort of disintegrated into powder. I assume the metal comes from the rim, but what's causing it to collect in certain places on the shoes? Is it that the rubber has pits in the surface already, which happen to collect the metal as it wears off? If not, what's happening?

I assume these bits of metal accelerate rim wear, so I'm thinking I'll check the pads occasionally in case it happens again, is there anything else I can do to deal with it?

Thanks in advance.

SJX426
10-28-10, 07:32 AM
What did you find when you examined the rim? Was it entirely smooth? Do the pads have the metal particles on all surfaces, indicating that it is embedded in the material at manufacture?
Airburst
10-28-10, 02:46 PM
The rim looks pretty smooth, and the metal's only in the face that contacts the rim, as far as I can tell.

OneIsAllYouNeed
10-28-10, 02:51 PM
I'd recommend replacing the brake pads with newer ones. Older pads have a tendency to get brittle and hard, particularly some models of Deore and Dura-Ace pads. They can be hard enough to wear the rim. The flecks of metal you saw were likely chunks of the rims.
dedhed
10-29-10, 09:23 AM
Replace the pads or at minimum, sand the old ones down.
RaleighComp
10-29-10, 09:29 AM
Replace the pads or at minimum, sand the old ones down.

+1

After you've cleaned/replaced the pads, clean the rims as well. A neat trick is to cut some pieces of a kitchen sponge and jam them in between the brake pads and rim and at very *low* speed, speed up and brake a few times. This will clean the rims nicely.

Also, want to set the straddle wires nice and low so that they form a 90 degree angle at pad/rim contact. The levers should feel very spongy, not hard when the brakes are set up correctly. Kind of counter-intuitive, but that's the truth.