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  1. #1
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    M666 Brakes rubbing on rotor

    I'm new to hydraulic brakes and have just finished installing a set on Shimano M666 brakes on my bike. After getting everything all set up and the calipers centered, the rotors are rubbing on the pads and making a sound that reminds me of of something being sanded. This can't be normal. Any ideas on how to fix the issue?

  2. #2
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    Readjust the calipers. Place the bike in a stand, so the wheels/calipers are at least close to eye level. Get a good vantage point from right behind the caliper, preferably with some light spilling through from the other side. Give the wheel a spin and watch the gap(s). If you only see one gap, you will need to readjust the caliper. If you see two gaps for most of the time, you will need to true the rotor (it doesn't sound like this is the case, so I won't go into it).

    Loosen the bolts on the calipers until they move freely without and force, then grab the brake lever (without the wheel spinning, of course). Gently snug up the bolts to just a little bit more than hand tight. At this point, you should be able to use your fingers to position the caliper until you see a gap on either side of the rotor. Give it a spin to make sure that it isn't rubbing, then hold the brake lever tightly, and start tightening the bolts, alternating one to the other, but not tightening either all at once.

    If this doesn't solve the problem, your brake mounts, be they posts or IS, will need to be faced.

  3. #3
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    I'll played with it a bit again this morning and the pistons aren't retracting. What's the fix for that?

  4. #4
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    Quote Originally Posted by swcreates View Post
    I'll played with it a bit again this morning and the pistons aren't retracting. What's the fix for that?
    Are they new? If so, they shouldn't do that out of the box. You didn't squeeze the lever without a disc rotor or pad spacer in between the pads did you?
    I don't crash, I just have slightly uncontrolled dismounts!

  5. #5
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    I agree, they shouldn't be doing that out of the box, however, you can try to solve the issue in a few ways. The first thing I will tell you, though, is that the pistons, without the pads/spring installed, will not retract by themselves (and won't retract the same amount they go out, anyway, assuming you have no rotor installed).

    Anyhow, the first thing to do is remove the pads from inside the caliper (and remove the caliper from the bike. Using a blunt, plastic coated instrument (tire levers work nicely for this) force the pistons back in the caliper body. They will move with very little effort if you present the force perpendicular to the piston, so don't force them.

    Actuate the brake lever now, and watch the pistons. Does one move and the other not? In this case, before proceeding with the next step, press the piston that moved back into the body, and hold it there (again, using a tire lever). Now actuate the lever again, and the 'stuck' piston should move out. It may be fiddly to do by yourself, but is very possible. Push the same (stuck) piston back in and repeat a few times, then remove the lever from the other piston and try actuating the lever again. If both pistons move an equal amount, you are good to go, if not, go to the next step.

    Get both pistons sticking out a ways from the caliper (be careful here, as you can pop them out, and then you will need to reassemble the system and bleed it) and take a cotton swab doused in alcohol (preferably denatured, but rubbing alcohol will work as well) and swab the sides of the pistons. Get another swab, and dip it in mineral oil, and work it around the sides of the pistons, then push them back into the caliper body. Clean up around the pistons now with another alcohol swab.

    After lubricating the pistons, the problem should be solved, and both should be moving freely.

  6. #6
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    Finally got it all sorted out. I recentered the calipers and for the back, bleed off some excess fluid. No more rubbing!

    Thanks for all the help!

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