Andrew R Stewart
Join Date: Feb 2012
Location: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder
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Jeez, if squealing brakes were completely understood they'd never happen, bike component makers would have figured out how already, but that's not real bike life. Various contributers are the causes. Flexible brakes, contaminated rims, clean rims (what?), new pads, old pads, pads contacting the rim at the wrong angle (both ways, toe in or out), wet rims and more.
So what do you do. First you "baseline" the system. Clean rims with solvent then alcohol (and sand paper sometimes). Clean pads with sand paper. Position pads to contact rims flat. Reduce any caliper/brake arm flex as can (pivot bolts tight, center bolt nuts snug). Test ride. If squeals continues then toe in pads, the rear end of the pad should contact the rim last, maybe a nickel's amount of pad angle to the rim surface. Test ride. Toe out the pads. Test ride. File a slight ramp on the pads and their segments mimicking the toe in but along the segments. Try different pads. Repeat the toeing. Sometimes it takes different pads on one brake.
Usually somewhere along this set of trial and sees you'll hear silence. But in the end my go to is to dirty the pads. I'll pick up some dirt or mulch and trap some between the pads and rim then ride. I have used this fall back many times while on a ride or after trying everything else I can do.
This is one of the Holy Grails of wrenching. Having a brake that stops strongly (remember that most of the methods to reduce squeal actually reduce the surface friction between the pads and rim) yet never squeals. As brakes (caliper and pivot boss mounted) have gotten stiffer this problem is less common but still we deal with it weekly at the shop.
When a customer comes into the shop complaining about noisy brakes the first thing I ask is if they still can stop... After all that's the most important function! Then if it is all the time regardless of how hard they are sopping or the conditions they're in (cold or wet). Sometimes i ask if they have ever head a car's brakes squeal and suggest that the automotive industry has far more $ and engineers trying to silence brakes then the bike business does. Then i say that we can probably reduce the amount or situations of squealing but that we can't completely eliminate it always. Then we try the above tricks. Andy.