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Are direct-pull brakes inherently bad?

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Are direct-pull brakes inherently bad?

Old 05-16-10, 06:32 PM
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Syscrush
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Are direct-pull brakes inherently bad?

Hey all.

My wife has a Miele hybrid that's a few years old now. She likes the bike a lot and uses it as her commuter - last year we did some longer sightseeing/fitness rides on it (50-75km) but now that she's got a nice little Trek 1.2, the hybrid is used for commuting & errands.

The one issue she's had with the bike since new, and that has persisted despite a couple of tuneups and my own best attempts to correct it is that the front v-brake keeps wanting to rub after a couple of hard pulls. I've done what I can with the adjusting screws, but it seems like no matter what I do, I can't get both sides to return to a neutral non-rubbing position every time.

She's asked 2 separate shops to correct this when she's had the bike in for a tuneup, and the result has been the same. Looking at the design I don't see how this wouldn't be a common issue, but I see plenty of people running this style of brake and not appearing to be bothered by this problem.

Does anyone have any tips on correcting this?

Failing that, is it possible to convert to a traditional center-pull canti setup?
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Old 05-16-10, 06:52 PM
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Sounds like there could be something wrong with the brakes, themselves. Might be worth it, to pick up a new set.

First thing to do, is make sure that the brake mounts aren't damaged, and that the brake's springs are actually going into the holes in the mounts that are supposed to hold them. (assuming your brakes are made to make use of those holes)

If they pivot on the canti post itself, then I'd lightly sand the post, and grease it. Definitely want to make sure that there's nothing there to cause any binding. If they pivot on a bushing that doesn't move on the post, see how freely it moves in relation to the brake arm. Could be something in there causing it to bind up. Not sure how to clean that out, other than a little compressed air, and some oil.

The other thing to check is whatever mechanism is supposed to be keeping the tension on the springs. It could be the tensioning screw is loose, and keeps backing out. Some threadlock should fix that, just make sure it's the kind that's meant to allow the bolt to be moved again.

If it's got a set up like the old set of Tektro V-brakes I have around here, where the spring tension is adjusted by a collar (with flats on it for an open end wrench) around the brake post that sits under the brake arm, you should probably just get new brakes. Something has worn to the point that the adjusting collar is no longer staying in place. On the brakes like that that I have, that collar is the bottom of a bushing that the brake arms ride on. It's held in place by friction from tightening the mounting bolt. Putting a washer under the head of the mounting bolt might help, but it would probably just be a band-aid fix.

I hope that last paragraph makes sense, Those Tektros are hard to describe.
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Old 05-16-10, 06:54 PM
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No problem with mine as far as this is concerned. Open the brake and try moving each arm by itself to see if one has a tight pivot or any binding that you can feel. You can try screwing both clearance adjustment screws in all the way and then backing out the one on the side with the largest gap until the gaps are equal. Then operate the brake a few times and correct clearance with the one screw that you did the initial adjustment with. This will increase spring tension slightly.

With good lined cable, properly installed, and the brake arm pivots well lubed and without binding you should not be having this problem.

Another possibility is that the arm return springs are set to be too weak. On the mounting studs there are three holes for the brake return springs. Try moving the arm springs to the next hole from where they are now to increase return spring force and see if that helps. The arms need to be removed from the studs and reinstalled to make this change.

If things are not right then cantilever brakes can have the same problem plus a change to cantilever brakes requires different brake levers too.
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Old 05-16-10, 07:39 PM
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I find direct pull brakes work really well if you remove the brake arms and clean/lube the posts every winter. I use superlube grease which is a light PTFE based grease. On a friends bike that I take are of, one of the brake arm screws has galled so that one won't come off. I turn the bike upside down and drip/work some superlube lubricant in there. His brakes work fine, too. Bike parts just like being clean and lightly lubed. bk
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Old 05-16-10, 07:43 PM
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Thanks to all. I have messed with the adjusting screws as described above a few times, so I think it's time to disassemble and do some clean & lube and also see if these brakes have that option of relocating the return spring to increase the tension.
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Old 05-16-10, 08:17 PM
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ProMax brake?

If that's the case, and you'd like to fix it permanently, I'd replace the brake caliper with something from Avid or Shimano.
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Old 05-16-10, 08:47 PM
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V-brakes are the best in my experience. After three years I realized it was time to replace them, and for $20 you can do both (Tektro). Night and day difference. The tension springs just lost their effectiveness, and no matter how well you adjust everything else, it's just not the same. spend the $20 - it takes about ten minutes to swap them out.
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Old 05-16-10, 09:09 PM
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Consider the possibility that the cable itself is pushing or pulling the brake to one side. This is usually more of a problem on rears brakes, because of the short loop of cable from the frame to the brake. It's also possible in the front, especially on a shorter women's bike whose low handlebar makes for a short brake cable.

If it turns out to be the cable try to find a different noodle with a bend that offers a better lead for the cable reducing the force it exerts on the arm. In one extreme case I solved the problem by eliminating the noodle, and setting up the cable in a broad 180° loop directly from the lever.
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Old 05-16-10, 09:21 PM
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I've also seen the brake noodle being close enough to a thigh to get pushed.

+1 on a set of Avid brakes if they are pro-max or similar junk.
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Old 05-17-10, 03:17 AM
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All good advice above. I've had an issue with Avid linear pulls that couldn't be resolved with conventional spring-tuning techniques. There just wasn't enough adjustment in the screw to make one side enough like the other. And stepping one side one whole hole on the boss was overkill. Spring tension is so low on these brakes. The solution lay in manual tweaking of the spring. With fingers, I bent the spring on the drag-prone side far enough out that it deformed slightly. Then, fine tuning with the screw adjusters resolved the issue to my satisfaction.
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Old 05-17-10, 06:04 AM
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If all else fails, adjusting V-brakes is often a matter of metaphysics. Joss-sticks might help. Ole Sheldon, he says that when adjusting V-brakes, if you tighten the spring adjuster on one side, then one must loosen the tension adjuster on the other. That and lube the pivots regular, I think. Cables can also move out of position, causing drag, as a fellow poster notes.
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Old 05-17-10, 08:35 AM
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I'd...
1. lubricate the brake pivots, and make sure they're moving freely
2. make sure the cables are moving smoothly in their housings
3. consider FBinNY's suggestion that the brakes are being nudged off-center somehow by their housing or the noodle or by being nudged by the rider. This might be fixable simply by tightening the pivot spring tension equally on both sides (either by tightening the little tension screws, or by disassembling and tightening the springs).

linear-pull brakes are pretty simple, I think. But also cheap and easy to replace with nicer linear pulls.


EDIT:
Yes, I agree with what peripatetic added below.

VVVV

Last edited by mcgreivey; 05-17-10 at 02:58 PM.
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Old 05-17-10, 11:44 AM
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Good suggestions here.

A few more for you. If the brakes are of lower quality, then likely the materials used--such as the springs and washers--are of lower quality. These are the kinds of things that can lead to chronic tension/centering problems. Therefore, and upgrade might be in order. Also, if you do remove the brake arms, check to see that the mount posts are straight. It's unlikely that they'd be off, but you never know. And maybe something's wrong with one or both of the set screws--if they are backing out for any reason from the force applied to the brake, this could lead to the arms getting off center.

As someone who's always dealing with sidepull caliper brakes, I think V-brakes are a cinch for centering and adjusting.
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