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Old 10-03-07, 11:18 PM   #1
Sizzle-Chest
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Worst Brakes Ever, Please Help!

I need help with my Dia Compe XCE cantilevers which are on my 1990 miyata grand touring 600. To summarize my problem, only one arm retracts after the brake is pulled. Before concluding that they are not adjusted correctly, please read on. I will try to explain it as quickly as possible.

Normally, the springs on a cantilever brake would go into the holes at the base of the boss. On these brakes, only the non-drive side is able to go into the hole. The drive side brake spring goes into a hole on a special piece of metal, which I’m holding in picture 1. This piece of metal becomes sandwiched between the brake arm and the base of the canti boss. It can then be adjusted using a 15mm cone wrench. (See picture 2)

The first problem is that no matter how much I adjust the piece of metal, the spring is still too loose to pull the arm back away from the rim after I brake. This is because the spring is not connected to the base of the boss but to that piece of metal. The non-drive side arm retracts fine, while the drive side arm with the special piece of metal stays against the rim.

The obvious solution would be to put new brakes on because these ones clearly don’t function properly. However, this is not possible because the bosses were designed to only be used with these brakes. At the base of the boss there is a piece of metal which actually makes the whole boss longer than a normal canti boss (see picture 3). So, when you put a normal cantilever brake arm on, the boss sticks out the end about 5 millimeters. The Dia Compe XCE fixed that by making the piece around the non-drive side boss longer than normal (see picture 4).

So, I have a set of brakes that don’t work at all, but they are the only ones that this bike will accept. I need help. Help me. Please!!!! Thank you!!!!
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File Type: jpg brake 2.JPG (40.3 KB, 129 views)
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File Type: jpg brake 4.JPG (40.3 KB, 117 views)
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Old 10-04-07, 02:34 AM   #2
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I've never heard of brakes with longer bosses on one side. What kind of frame is it?


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Old 10-04-07, 04:35 AM   #3
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A) What's preventing that metal disc from adjusting properly?

B) Have you tried another set of brakes on this bike?

To me it doesn't look like the left side is bigger. It looks like the right side is smaller. No, I'm not being a semantic ass. The left one looks like it's the right thickness, the right one looks too thin. Find a $10 Sally or yard sale bike with cantis and try them, you might be suprised.
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Old 10-04-07, 06:51 AM   #4
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Here's a link to some cantilever brake repair information:

http://www.parktool.com/repair/readhowto.asp?id=19

It is unclear why the drive side spring adjuster does not work. I have to guess that the spring:
a. has lost some tension over time (weak spring).
b. is broken.
c. came loose.


I expect that the spring requires a certain preload and that spring adjuster varies that load ~ +/- 20%. That means the spring has to be coiled before fitting into the spring adjuster for the drive side cantilever to work properly.
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Old 10-04-07, 07:04 AM   #5
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you do know you have to adjust the spring tension and then lock it in place with the pivot bolt? the only other solution is to get a similarly designed set of brakes, like the diacompe 986s.
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Old 10-04-07, 07:07 AM   #6
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i have tried several other sets of canti brakes on the bosses but they are all too short. both bosses are longer than normal. the reason they won't stay adjusted is because the spring is one coil shorter than normal in order to fit that metal piece, so the action is weak. and like i said, i have been adjusting them correctly by holding tension on the metal piece with a wrench then tightening the pivot bolt. BTW, the frame is a miyata grand touring 600. thanks again for any help!
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Old 10-04-07, 07:18 AM   #7
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Yeah, that style of canti can be tricky to balance properly.

From the pictures you provided (thanks for that, it really helps) I can see you have several tension holes to choose from. Since the adjustable side is functioning, try running the non-adjustable side spring (non-drive side) one hole lower, giving less tension. This may allow you to compensate for the weaker spring within the opposing arm's adjustment range.

I've often had to run each spring in a different hole, even on more standard cantis to compensate for unequally worn springs.
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Old 10-04-07, 07:27 AM   #8
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I'm sorry, I don't have any advice for you regarding your current brakes. But I do sympathize with you regarding the funky canti's on your older touring bike, particularly since they're Dia Compes. I've got an '83 Centurion Pro Tour, another very nice older touring bike, it also has Dia Compe canti's, and the bosses are configured in such a way that a better set of canti's won't work. My solution? I'm thinking of cutting the bosses completely off and grinding the area smooth, and then repainting. Then I'm going to install centerpull caliper brakes, mounted at the fender holes on the seatstay bridge and fork crown. I'll have plenty of reach, as well as room for plump tires and fenders. I hate those Dia Compe canti brakes-
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Old 10-04-07, 07:28 AM   #9
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i'll give that a shot wordbiker. i ride this thing fixed gear over the winter, and i have always been against riding brakeless, but i'm at the point where i'm actually considering it, so hopefully that works. as samuel l jackson would say, I've had it with these motherf*cking brakes on this motherf*cking bike!
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Old 10-04-07, 07:38 AM   #10
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I can understand the frustration.

Even if balancing doesn't work out, you may not be totally stuck. There is a tool called a brake boss mill that could potentially take off that lower shoulder on the boss, allowing you to run more standard cantis. I haven't used one for that purpose, but it may be worth an inquiry with a local shop offering that service to find out.
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Old 10-04-07, 09:37 AM   #11
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I've got Diacompes similar to these (mine are XC-Masters). When you are installing the drive-side (on the front wheel, non-drive on the rear on my old 90-91 Iguana) arm, you increase the tension by turning the 15mm wrench on the floating metal bit downwards _as you tighten_ the mounting bolt, not afterwards. I find the tension on mine is about right when the top wrench flat is about level or tilted slightly away from the fork.

Hope this helps, and many apologies if you already know all of this.

Does anybody know what the design concept is with this type brake?
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Old 10-04-07, 10:24 AM   #12
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Another option, similar to what worldbiker suggested, is to drill another hole in the drive side tension adjuster. The hole would need to be offset (probably 45 deg on the same radius) to take up more slack in the spring and allow it to coil tighter. It might be just as well to drill two symmetric holes on the tension adjuster since its as much trouble as drilling one.

Not to get too technical here, but did you know you can buy another spring or a spring with more tension? All those springs are carbon steel (music wire) torsion springs. Knowing the spring wire diameter, number of coils, and orientation (http://www.harris-springs.com/torsion-springs.html) is all the necessary information. It might cost about $12.00+s/h (mostly because of minimum orders and your country). Depending on your sentimental attachment to the bicycle frame, modifying the brake boss and getting a standard set of brakes would be the best long term fix.
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Old 10-04-07, 12:57 PM   #13
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Another option, similar to what worldbiker suggested, is to drill another hole in the drive side tension adjuster. The hole would need to be offset (probably 45 deg on the same radius) to take up more slack in the spring and allow it to coil tighter. ...
This wouldn't change anything-

Sizzle- on mine the floating metal plate is free to rotate 360 degrees- so no extra hole would be necessary, just keep turning the plate until there's enough tension on the spring... is this not the case with yours? Is the spring slipping out of the hole inside the arm? Mine _really_ likes to do that when I'm reassembling...
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