Bicycle Mechanics - New disc brake rubbing?
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New disc brake rubbing, is it normal for a brand new mechanical disc to rub initially as it beds in?
My lbs said it would rub at first, I have adjusted them both out a bit and the rear one is now free but the front one still rubs slightly.
I just about killed myself with exhaustion riding my new bike home due to the rubbing. :)
09-17-05, 06:51 AM
You might expect a *little* rub with new discs... but you shouldn't get exhasuted from it!
What are the brakes?
They are tektro io brakes.
The ride home is all uphill and gets steeper the closer I get to home luckily the pedalling started getting a bit easier toward the end. When I checked the brakes they were both still rubbing significantly (the mechanic at the lbs may have been in a bit of a hurry setting them up as they were having a busy day), after adjusting them myself the back is completely free but the front still rubs slightly.
I will plumet down some of the local hills tomorrow, weather permiting and see if that helps bed them in.
I was thinking afterwards that I have pedaled 1 of my electric bikes home with a dead battery and I think that might have been easier than this ride.
09-17-05, 12:50 PM
Tektros aren't exactly top-shelf brakes, but being in a hurry never helps when you're setting these things up. If the rub is significant, I'd say take the bike in and have 'em set it up right. If the rotor only rubs when the wheel is in a certain position, definitely have 'em take a look and true the rotor as necessary. At the very least you should be starting out with straight rotors. If you want to try it yourself the method I usually use is as follows:
Back the free side way off (so it doesn't touch at all) and turn the fixed pad, eh...most of the way in. Leave a little play.
The mounting bracket should be slotted slightly (I'm not 100% positive about Tektros) to allow you to move the caliper side to side and align it with the rotor. Align it with the rotor so the fixed pad just *barely* touches. If your mounting hardware lacks this feature, set your fixed pad so it's just barely touching the rotor and go to the next step.
Using the tiniest of increments, back the fixed pad off so it doesn't touch anymore. On most systems you can peer through the caliper and see that the pad should line up with the rotor maybe half a mil off it. The closer you can get the fixed pad to the rotor without it touching, the less your rotor will deflect when you pull the brake. Deflection + heat + time = warped rotors.
Cable tension should be set so that the actuating arm is all the way at the end of its throw. Some systems don't allow you adjust the free pad, all I can say is make do with what you got there. ;) Just adjust the free pad in until it barely touches, back it off until it shuts up, double check your lever throw and that's it. If you need to make any adjustments, always try to adjust the free pad and leave the fixed one as close to the rotor as possible without touching. Even with entry-level stuff you should be able to eliminate all but the faintest bit of noise and any dragging, a mechanic who tells you different is either in a hurry or being lazy, your pads may be wearing or contacting unevenly or the rotor might not be perfectly straight. It isn't *normal* because I can make everything I've worked on to date run quiet right out of the box at at the very most it'll rub faintly like...when you flex the fork or frame (sometimes mounts required facing, bike shops have tools for that). Not what you're describing.
Sorted, I backed it of a touch more so you could hear it rub but it didn't affect spinning the wheel.
Then rode down a few klm of steep tracks (after climbing them)they are great now.
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