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Need some help on disc brake setup

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Need some help on disc brake setup

Old 04-04-10, 02:37 PM
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Need some help on disc brake setup

I'm helping a buddy put his BD Motobecane together. Overall, the quality looks good and the thing has gone together really easy. Wheels were true out of the box, small tweaks to derailleurs including raising the front der slightly. Blah blah blah.....

It's my first time setting up disc brakes. This one has mechanical Tektro's (low end, likely the cheapest ones they make). They really grab nicely, stopping power is good and it has me thinking of making the switch. However, when I turn the bike or lean in either direction I can hear the front disc rub. It's not enough to create any real friction, but annoying. Is this typical? Someone please give me some education. I've spent a lot of time adjusting the pad clearance on both sides of the rotor and even tried to "true" the rotor.

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Old 04-05-10, 11:45 PM
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You might want to check for the cable pulling or moving in a way that tightens up the brake when you turn.

You seem to have looked at how the pads adjust and how the rotor tracks. Use a flashlight to see if the rotor is running closer to one side in a spot or two, and carefully tweak it.

Check the caliper to make sure it is pretty well lined up with the disc.

You could also try backing out both pads until you get no rubbing at all. You might have a fixed pad that moves in clicks or detents. Move it in until it just begins to rub. Then back it out until it just stops. Then back it way out while counting the clicks or turns. With it backed off, set your moving pad until it just barely doesn't rub. Then return the fixed, countable pad, back to it's no rub position.

You'll might also want to squeze the brake regularly as you make all your adjustments, as it might affect the final pad position after an adjustment.

It could also be that the pads are held a little loosely, and can move a bit. As long as they seem to be secure as designed, this may not be a problem.

You might find that you have to compromise between a little rub and nice tight brakes. I wouldn't get to worried about a little rubbing, expecially on cheaper brakes. You friend probably won't even notice it when he rides.
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Old 04-05-10, 11:50 PM
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It's not the "by the book" way of adjusting mechanical disc brakes, but I've had good luck just moving the pads until they just start dragging, then backing off a click or two for both the fixed and movable side. If the discs are free normally, but rub when the wheel is loaded, then you might back off another click - I bet you still have plenty of brakes. If loading the wheel is a continuing rub issue even with the brakes properly adjusted, then I'd start looking at bad wheel bearings, binding cables, etc.

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Old 04-06-10, 12:23 PM
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It is possible to have everything correct and still get rubbing under load or when there is flex. I have a friend that is a little heavy and he gets a slight drag or rub when turning. Not enough to slow him down but like you said it is frustrating. I tried to adjust it for him, he took it to two shops that have good mechanics and they told him it was flex and there was nothing he could do. Now when he rides my bike there is no rubbing at all. If the wheel is true, the disc is straight, the rim has no play side to side, I would almost think there is not much he can do. Have you tried checking the front shock for flex from side to side?
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