Bicycle Mechanics - Brakes locking too easily
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05-04-06, 03:20 PM
I had the front wheel of my folder rebuilt at Toga. They adjust the brakes as part of it (thanks!), but on my way home I nearly had the living daylights scared out of me when the brakes locked with almost no pressure on the levers. I've been riding for a very long time so I can tell you that something's not right. The pads were fairly worn so I replaced them with the hope of fixing the problem. The same exact thing happens with the new pads! So I went back to Toga today and, after trying the bike themselves, they concluded with a big "you're right, something's wrong but we can't pinpoint the cause".
Anybody ever hear of this happening? FYI, the front wheel has a Pantour suspension hub. I wonder if that has anything to do with it.
Edit: We're talking V-brakes here.
05-04-06, 03:43 PM
Cable-operated brakes? If cables, housings and levers are in good shape, I would take apart the caliper, clean it, grease moving parts and reassemble. You should be able to isolate the problem to either the caliper or the rest of the operation by holding the disconnected cable, then pulling and releasing the lever.
05-04-06, 03:51 PM
Thanks for the tip. Any idea on why this would happen so suddenly, out of nowhere? The only change really was the wheel rebuild, unless the Toga guys did something funky when tightening the brakes the first time.
05-04-06, 05:51 PM
Probably the rim has extra friction with it for some reason. Being new and all that. Slacken your brake adjustment. You should be getting just to be able to lock up with full lever depression.
05-04-06, 06:15 PM
Actually it's the same old rim with new spokes. Weird, no?
05-04-06, 06:18 PM
Could they have cleaned the braking surface to work on it without getting filty? The residue from the cleaner might be causing the pad to stick. Wipe em down with water and see.
05-04-06, 06:25 PM
Hmm, good idea. I'll clean off the rims (the pads have been replaced with new ones, as mentioned above, but will give 'em a wipe too).
Your cable is just to tight. Let a couple mm slide out at the caliper. They probly cleaned the rims and pads which increases stopping power and also (over)tightened the cable tension a little bit. I cant think of any cleaner that would leave a sticky residue, that would defeat the purpose. A strong degreaser will evaporate leaving no residue, and a weaker one may leave a slight residue that could only be desribed as slick.
05-04-06, 08:58 PM
Ah, but the cable has been loosened to no effect. It's really a mystery. I'm inclined to believe the theory that something is wrong with the arms of the V-brakes.
Edit: to clarify, the cable has been loosened but a little more pressure (duh) is needed to make it lock-up. It's still very un-natural.
Edit 2: I'm obviously an idiot for not stating in the first post that they are V-brakes.
05-04-06, 10:43 PM
Longshot here but I wonder if you might be expiriencing some pad dive? I usually see this on cheaper rims that arent square, iow, the braking surface angles slightly. When the brake is applied the pad is compressed at such an angle that the return springs cant pull the pads off the rim. Is this whats happening, perhaps?
05-04-06, 11:54 PM
Make sure the pads aren't catching the tires, as well. You might try a new brand/kind of brake pads eventually.
So the pads move up and down on the rim when you brake?
05-05-06, 07:48 AM
They move on an arc raather than a straight line so as pads wear they strike the rim at a lower point. Shimano's parallel-push addressed this witha linkage that would keep the pads in line with rim even as pads broke down.
05-05-06, 08:39 AM
The pads definitely are not catching the tire. If anything, they move down the rim with the Pantour suspension. I've followed directions carefully, using thin ThinLine pads, setting the pads high on the rim to account for the suspension. I haven't had a problem in nearly a year of owning this bike, this newest set being the third set of pads on it.
05-05-06, 09:04 AM
You're not by any chance using XT brake levers, are you? They had (for a awhile, anyway) little adjustment blocks that could be removed to create more leverage, increasing braking power. The way it worked is that you left both blocks in for the least amount of leverage, remove one block for a little more leverage, and remove both blocks for the highest leverage. The blocks are little plastic pieces, very small. With both blocks removed, the Shimano instructions give a warning that you might crash by going over the bars, or something like that, if you don't take it slow at first and get used to the increased leverage. I currently have a mtb with this setup, and I had to install brake boosters front and rear (Shimano highly recommends this also with both blocks removed) to stiffen the frame and fork adequately, to prevent excessive flexing. Aside from discs, I can't imagine stronger brakes on a bicycle.
If you have these levers (or something similar), maybe the mechanic inadvertantly removed the blocks, and leverage has been dramatically increased.
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