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I just installed a new front disk brake and the rotor rubs a bit once per rotation. If I take the rotor off and place it on flat surface, it seems totally flat but once installed I can see/hear it rubbing onto the installed disk brake caliper once a rotation. It's enough friction that it's making the wheel stop spinning pretty soon compared with when spin it with the brake off(not sure how to quantify it)

Is this normal?

(The new brake is an hydrolic Avid 7 Elixer and it replaced the original (also hydrolic) Avid 7 Juicy that came with the bike. It's the original rotor. The fork is a Lefty and therefore there's not any adjustment to be done on the wheel.)

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As I understand it (I religiously avoid disk brakes myself), you should expect some rub with a new bike (or, presumably a new brake on an existing bike), until the brakes have "bedded in" (whatever that means). –  Daniel R Hicks May 11 at 13:14
    
Is it catching on the toe of the pad? I've seen that this leading part of the pads wears fast to no noticeable effect on the braking power. –  DWGKNZ May 11 at 21:17
    
You fitted a new rotor, did you turn back your brake adjuster screws (if you are non-hydraulic)? Try to tighten the rotor on the hub in a star pattern slowly. Also maybe try to move the caliper in the mount a bit, after loosening the adjuster screws. –  sessyargc.jp May 12 at 2:35
    
@DWGKNZ I don't think it's catching just the toe...I think the radius of the rotor is rubbing. –  Alex May 12 at 8:33
    
@sessyargc.jp No, it's still the old rotor on there. And it's hydraulic (Updated Q to clarify that.) The install instructions are to loosen the brake mounts, squeeze and keep closed the handbrake and then look down the brake mounts. (actually, I'm not sure what you mean by moving the caliper mount...do you mean the whole brake?) –  Alex May 12 at 8:35
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2 Answers 2

Some rub is OK. No rub is optimal. Normal riding can bend the rotors, so the "no rub" situation never lasts forever. This can be fixed though.

You can adjust the caliper to reduce rub (or completelly eliminate it). The bolt holes are not very tight so you can play around with offseting the caliper accordingly. Just unscrew the 2 allen bolts a bit and start playing around with offsets. Looking through the brake pads and disk to a bright coloured floor (e.g white) makes this process very easy.

If the space of the pads is not enough to allow zero rub then you can try to straighten the disk. Use a clean rug/paper towler to grab it and give it slight push or pull on the spot it's bent. Never touch the rotor with your hand because the hand has a bit of oil which can reduce the performance of your brake.

The fact that your brake is new doesn't mean that it should be 100% rub free. There is a small possibility that the hub 6 bolt platform is slightly off. So a new disk will always look bent when rotating between the pads.

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I wondered about the hub 6 bolt being slightly off since the rotor seems flat when i take it off. I'll try to readjust it at the point that it rubs...not sure why I didn't think of that.. –  Alex May 12 at 8:37
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If you're getting rub once per revolution, the rotor is not flat and should be trued.

You can try to true it in-place by trial and error, or for best results use a dial indicator in a truing stand to really get it flat. With some practice and patience, it's possible to true a rotor within 0.05mm or less. Testing a rotor by placing it on a flat surface is not anywhere near precise enough to completely eliminate brake rub.

Make sure that once you've trued the rotor, you don't bend it out of shape again while installing it. It's easy to accidently bend it by engaging the brakes when the rotor is far out of center between the shoes - check visually that the shoes are at least somewhat close before pulling on the brakes.

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