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Brake keeps coming loose

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Brake keeps coming loose

Old 06-29-09, 06:02 PM
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Brake keeps coming loose

I have some old Dia-Compe sidepull brakes. They work fine in stopping the bike, but the front one constantly comes loose. it has a post that mounts to the bike, and that isn't the problem. The problem is that the nuts that hold the arms in position come unscrewed with use of the brake. I've already ruined one brake because I had to slam it on and it was loose (bent the post), so I'm really conscious of not doing it again. I can only tighten the nuts so far, which is reasonably tight, before it keeps the arms from retracting (i.e. before it prevents the spring from springing). Is there something I'm missing? Is the spring just worn out, assuming I'm supposed to be really screwing the thing down? Maybe I'm missing a washer or something...but it seems like everything is there.
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Old 06-29-09, 06:42 PM
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Are you tightening them properly? There should be two nuts holding the caliper arms onto the pivot bolt. The inner nut sets the adjustment (you likely need a thin brake wrench to do this right); the outer nut is a locknut to prevent loosening. You tighten the inner nut down against the arms until there's no slop in the arms, but not so tight that they can't pivot freely. Then you use the thin brake wrench to hold it in place while you tighten the locknut against it. It's pretty common for it to come out a little tighter due to the tension on the bolt, so you may have to back the inner nut off a little to let the caliper arms move freely again. It may take some trial and error until you develop a feel for how it works.
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Old 06-29-09, 06:50 PM
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Go to this Park Tool - Sidepull Brake Service site. Look specifically at the "Double Nut Adjustments" section about 75% of the way down. You need TWO nuts on the end of the bolt to lock down the caliper-arms. If you're missing a nut, the remaining one will work itself looser each time you apply the brake.
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