Help with Dia-Compe XCT cantilever brakes
06-23-11, 09:25 PM
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Help with Dia-Compe XCT cantilever brakes
Greetings, all,
My girlfriend is the original owner of a 1990 Trek 720 Multi-trak. All components are original, including Dia-Compe XCT cantilever brakes. Recently, we have been trying to get back into cycling, and on our rides her rear brakes have been squealing badly. To my senses, the brakes seem mushy though the handlebar levers seem well-adjusted. I spoke with the LBS who advised that the brake pads were old and probably dried out and should be replaced. I bought pads, cleaned the rims with rubbing alcohol, and replaced the pads but the squealing continued.
I noticed that the brakes did not seem to be centered about the rim and that the left cantilever does not seem to function. After reading the FAQ here and articles on Sheldon Brown's site, I decided to remove the brakes from the bosses, grease them up, and try to adjust the springs. The left side came apart easily. Contrary to what I read on SB's site about Dia-Compe brakes, it seems to me that the spring pin passes through a bushing and sits in one of the three holes on the frame's brake boss. The right side is very difficult to remove for reasons that are as yet unclear to me. I can remove the bolt which holds the brake to the boss but it is very difficult to get the brake out. And once I do get the brake out, it is very difficult to reseat.
I assume that the side that has the big gap should have the spring adjusted to have lower compression and/or the side with little gap should be have higher spring compression. But I fear that something worse is going on if I have so much difficulty removing the brake from the boss. Do any of you have any advice for me regarding what might be going on here? I'm trying to come up the learning curve but haven't ever worked on bike brakes before.
Thanks in advance!
My girlfriend is the original owner of a 1990 Trek 720 Multi-trak. All components are original, including Dia-Compe XCT cantilever brakes. Recently, we have been trying to get back into cycling, and on our rides her rear brakes have been squealing badly. To my senses, the brakes seem mushy though the handlebar levers seem well-adjusted. I spoke with the LBS who advised that the brake pads were old and probably dried out and should be replaced. I bought pads, cleaned the rims with rubbing alcohol, and replaced the pads but the squealing continued.
I noticed that the brakes did not seem to be centered about the rim and that the left cantilever does not seem to function. After reading the FAQ here and articles on Sheldon Brown's site, I decided to remove the brakes from the bosses, grease them up, and try to adjust the springs. The left side came apart easily. Contrary to what I read on SB's site about Dia-Compe brakes, it seems to me that the spring pin passes through a bushing and sits in one of the three holes on the frame's brake boss. The right side is very difficult to remove for reasons that are as yet unclear to me. I can remove the bolt which holds the brake to the boss but it is very difficult to get the brake out. And once I do get the brake out, it is very difficult to reseat.
I assume that the side that has the big gap should have the spring adjusted to have lower compression and/or the side with little gap should be have higher spring compression. But I fear that something worse is going on if I have so much difficulty removing the brake from the boss. Do any of you have any advice for me regarding what might be going on here? I'm trying to come up the learning curve but haven't ever worked on bike brakes before.
Thanks in advance!
06-24-11, 11:35 AM
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Some brief updates: I read on ParkTool.com that one should select the middle hole on the boss for the spring. Not sure how to adjust spring compression then.
I think in fact it is the frame boss itself is damaged. I removed both cantilever sides simultaneously and tried the left (easy to remove) side on the right boss (post?), that is to say the difficult to remove side, and vice versa. Neither through hole wants to go over the right post on the frame, while both will go over the left.
The conclusion I draw from this is that the right post has either been peened over or has always been oversized. My girlfriend recalls that the brakes have "always" been noisy, though I find it hard to believe that we wouldn't have exercised the warranty right off if this had been the case. I'm thinking that somebody at one of the bike shops we used to go to overtightened the retaining bold and compressed the post to the point of deformation.
I'm not sure how to fix this. I imagine I could try to take emery cloth to the post and try to machine it down, but I can't imagine that it will be easy to maintain circularity.
I think in fact it is the frame boss itself is damaged. I removed both cantilever sides simultaneously and tried the left (easy to remove) side on the right boss (post?), that is to say the difficult to remove side, and vice versa. Neither through hole wants to go over the right post on the frame, while both will go over the left.
The conclusion I draw from this is that the right post has either been peened over or has always been oversized. My girlfriend recalls that the brakes have "always" been noisy, though I find it hard to believe that we wouldn't have exercised the warranty right off if this had been the case. I'm thinking that somebody at one of the bike shops we used to go to overtightened the retaining bold and compressed the post to the point of deformation.
I'm not sure how to fix this. I imagine I could try to take emery cloth to the post and try to machine it down, but I can't imagine that it will be easy to maintain circularity.
