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Cantilever brake plastic part broken

Old 12-27-13, 07:17 AM
  #1  
goldfinch
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Cantilever brake plastic part broken

My old mountain bike has cantilever brakes. They always worked well until now. On the front brake the plastic part which goes over the spring cracked on both sides. Now I can't get the brakes centered as you can't adjust the spring tension. It is bad enough that I can't adjust them well enough to avoid brake rub.

I am on the road with RV and bikes, currently traveling through Missouri and Kansas and soon to be in Arizona. Is this part available anymore anywhere or should I replace the entire front brake? If I have to replace the brake are there any that are relatively inexpensive yet don't use a plastic piece like on these Shimano brakes? The bike is pretty low end and I just use it for riding in really crummy conditions.
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Old 12-27-13, 07:28 AM
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I believe that plastic part is just a cover to keep crud off of the spring. I don't think you need it to center or adjust the brake position.
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Old 12-27-13, 07:38 AM
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Originally Posted by HillRider View Post
I believe that plastic part is just a cover to keep crud off of the spring. I don't think you need it to center or adjust the brake position.
The adjusting screw on one side makes no adjustment. I figured it was because of the broken plastic. What else could be the issue? Old failing springs?
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Old 12-27-13, 07:40 AM
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Do both arms move freely? Maybe dirt got into the pivots and is binding one or both sides.
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Old 12-27-13, 07:43 AM
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That's a quite common issue. A decade or so ago, Shimano even used to provide no cost replacements. I've probably fixed a hundred of them.

One work around is to twist a wire around the cracked plastic part to hold it together. My current solution is to replace the canty with a low end Shimano V-brake and lever.
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Old 12-27-13, 07:46 AM
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Originally Posted by HillRider View Post
Do both arms move freely? Maybe dirt got into the pivots and is binding one or both sides.
I took them apart and cleaned them. No change.

Originally Posted by Retro Grouch View Post
That's a quite common issue. A decade or so ago, Shimano even used to provide no cost replacements. I've probably fixed a hundred of them.

One work around is to twist a wire around the cracked plastic part to hold it together. My current solution is to replace the canty with a low end Shimano V-brake and lever.
So it is the plastic? I can try the wire trick until I get to Arizona and see if that works.

Anyway, off to hit the road and I'll check back later.
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Old 12-27-13, 08:23 AM
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The plastic spring cover does effect the spring's ability to pull the canti arm back away from the rim, as others have said. The lack of (cracked or when the cover finally breaks off completely) this cover DOESN'T effect the brakes stooping ability, just that the pads will be more likely to rub all the rims, not a situation that many will be happy with.

These days a low cost (Shimano CT90) replacement is the best solution and one that we do routinely at work. The new cantis cost only a tad more then new pads and the labor to install (at a shop) is only a few $ more also. The current cantis (CT90s) last a lot longer, not having the same design/material as the old ones. Andy.
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Old 12-27-13, 08:47 AM
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Originally Posted by Andrew R Stewart View Post
These days a low cost (Shimano CT90) replacement is the best solution and one that we do routinely at work. The new cantis cost only a tad more then new pads and the labor to install (at a shop) is only a few $ more also. The current cantis (CT90s) last a lot longer, not having the same design/material as the old ones. Andy.
Good, that's nice to know. I had Shimano LX cantis on an early 90's Trek MTB and the plastic ring also cracked. I zip-tied it back together.

RG's recommendation for replacing them with V-brakes is also good but gets into a lot more components, time and money since the levers also have to be changed and the OP is in the middle of a major road tour.
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Old 12-27-13, 09:14 AM
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Originally Posted by goldfinch View Post
So it is the plastic? I can try the wire trick until I get to Arizona and see if that works.

Anyway, off to hit the road and I'll check back later.
If you are in the Tucson area, you may be able to find parts at BICAS which is the local coop. Lots of used parts.
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Old 12-27-13, 02:34 PM
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Originally Posted by HillRider View Post
Good, that's nice to know. I had Shimano LX cantis on an early 90's Trek MTB and the plastic ring also cracked. I zip-tied it back together.

RG's recommendation for replacing them with V-brakes is also good but gets into a lot more components, time and money since the levers also have to be changed and the OP is in the middle of a major road tour.
To be clear, this isn't a major road tour. It is just spouse and I, five bicycles, motorhome and car on the road. I live in a motorhome most of the time. I will try a temporary fix as I have plenty of wire. My other hobby is jewelry making.

Originally Posted by cyccommute View Post
If you are in the Tucson area, you may be able to find parts at BICAS which is the local coop. Lots of used parts.
Thanks for the tip! I would like to replace parts if I can for cheap as this bike is a beater. Otherwise, I'll get new brakes for the front. Because I would prefer not to have to buy levers to I'll probably stick to the cantilever brakes.
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Old 12-27-13, 10:42 PM
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The broken plastic piece is still very common today on those old cantilevers. We used to replace them all the time. It's one of the first things I check when a bike with those come in. Now, we just put new low end Shimano or Tektro brakes on the bike. The price of new brakes is just a tad higher than the plactic piece. Since it is still a common problem, I don't think you will have a hard time finding the low end brakes at a shop. The shops I have worked always kept them in stock.

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Old 12-28-13, 01:28 AM
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brakes are labeled Altus/SLR right?
yep, design flaw
use of plastic to bear spring load, they all failed inevitably
dont bother with the replacement sleeve, just swap the entire brake with a better one
look at where the spring tension screw attaches on any potential replacement brakes, be sure its threading to metal
replace the rear while you're at it because they will fail too
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Old 12-29-13, 08:02 PM
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This has been my solution on two bikes with those same brakes with the same issue. Easiest part I have ever installed and they work great.

https://www.nashbar.com/bikes/Product...77_-1___202421
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Old 01-04-14, 06:20 PM
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Originally Posted by cyccommute View Post
If you are in the Tucson area, you may be able to find parts at BICAS which is the local coop. Lots of used parts.
Your tip was excellent. I got there today, dug through their used brake bin, found Deore cantilever brakes with metal not plastic to replace my broken brake and bought it for cheap. I installed them and they work perfect. Finally no brake rub!

BICAs looks fun. I am planning to go in Monday night where they are open for women and transgendered people. Spouse has a broken spoke and I want to learn how to replace spokes and true up a wheel. I also am looking at volunteering there; which should help improve and reinforce the skills I do have.

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