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Old 09-03-02, 05:26 PM   #1
geno
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Moutain bike brake problem

How tight should you make the bolts that hold int brake into the boss? One of the 2 brakes after squeezing the brakes does not spring back but merely stays where it is. If I back off the bolt to the boss a bit, it works fine. The spring is in the topmost position on the boss. Bad spring? Bad brake? Bolt too tight? Thanks.

Photo is the bad brake...
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Old 09-03-02, 07:14 PM   #2
John E
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First, unhook the brake cable, to make sure that one side really is binding, and is not being overpowered by the other. If it is binding, proceed to step 1, below. If not, try step 2.

1) Clean and lubricate the pivot point in question. Next, examine the construction of the pivot and the bolt. In many systems, the unthreaded shoulder of the bolt should be just long enough to accommodate the pivot bushings without binding; in others, you will have to back off slightly for proper operation. In the latter case, there should be a lock nut or some other system to hold the adjustment and to keep the bolt from coming loose.

2) Many cantilever brake systems have a small adjustment provision on ONE side, to help with centering.
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Old 09-04-02, 02:14 AM   #3
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The bolts should go on until they bottom out and then be tightened moderately snug, perhaps 60 inch-pounds. The brake's bushing should be shorter than the stud's pivoting area, so it shouldn't matter how tight the bolts are... in theory.

In reality, sometimes the brake's bushing is too long and it gets trapped between the bolt and the base of the stud, when the bolt is tightened all the way. One solution is to shorten the brake's bushing a little, using a hand file or perhaps a rotary tool with a cutting wheel. Another option is to lengthen the pivot area of the stud using a Bicycle Research brake-boss mill or some careful hand filing.

Those steel-core Shimano cantilevers also had a tendency for the springs to bind. The ones that featured 2mm allen-key adjusters were even worse, since the plate which the adjuster rotated was prone to getting cocked sideways. Judging by your photo, it appears you don't have the type with the adjusters, so that's one less headache.
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Old 09-04-02, 06:53 PM   #4
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Thanks for all the suggestions. Tried them all. Then I noticed on the good side that the spring that pokes into one of the 3 tension holes protruded through the hole furthur than the other side. I reversed the spring (which by the naked eye looked the same both ways) and presto. So I greased it and put lock tite into the post. LBS did maintenance check/adjustment on this bike in July - never again.
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