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  1. #1
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    Caliper misaligned with disc.

    Hi,

    I noticed today that my rear brake pistons were very uneven. One was extended a lot and the other hardly at all.

    So I pushed the extended one in, and went to put the caliper back on the bike, but I very quickly realized that to get the disc to go through the middle of the caliper (and pads since the pistons are now even), my caliper has to be pushed right to the extreme left, leaving me no play at all. So if I ever need to realign and push the caliper a bit further left, I can't.

    It's a Trek Remedy 7 and the brakes are Avid Elixir CR's

    Has anyone had this problem before? Know what causes it?


  2. #2
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    bleed the system
    '11 Jedi
    '01 Straight8
    '01Rocket88< ran over it.. always do a full walk around!
    '00 Homegrown

  3. #3
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    Quote Originally Posted by shwinn8 View Post
    bleed the system
    That won't help (and I did it a month ago anyway). This is an alignment issue.

  4. #4
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    Yes. You have a sitcky piston and need to free it (you should work on both of them as it's likely neither one is moving as freely as designed). Bleeding alone will do little to nothing, although depending on the age of the brakes, it may be a good idea to do a thorough fluid change - fluid that has absorbed water, which DOT fluid will always do over time, leads to sticky pistons.

    The basic process is to clean the side of the pistons with 90% rubbing alcohol. Once dry, push the pistons fully back into their bores, extend them again, and repeat until they move evenly.

    Now, since one piston is extending very little, you have to get a little creative to get it to extend more to clean the sticky part of it. Start by pushing the other piston back into its bore. You then need to find a way to restrain that piston while you squeeze the lever so you can get the sticky one to extend. I created a sort of jig that is simple but effective (held in a vise here for easy photographing):



    With the jig in the caliper slot, one piston will be restrained while the other is allowed to fully extend. Although this jig was slapped together, you can spend a little more time on it so that it will not allow the piston to overextend (taping a dime or penny in the center section may do the trick). If you happen to extend the piston too far, you're headed for a bleed.

    With the sticky piston extended, clean the sides and repeat the process outlined above until both pistons move evenly.

    Short of freeing the sticky piston, if you find you need to move the caliper more outboard to center it, you should be able to easily push the rotor more inboard instead. Gently push it inboard by hand, just as you would if you were trying to correct a slight warp, except be sure to do it evenly around the circumference of the rotor. Protect the rotor with paper towel as you do this to avoid getting any skin oils on it.

    Good luck,
    Pete
    I can barely get my mouth around it.

  5. #5
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    Thanks for all that, but unfortunately this is not my problem. The pistons ARE now evenly extended and working well, but my caliper needs to be to the far left, which is strange.

  6. #6
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    Quote Originally Posted by peanutaxis View Post
    Thanks for all that, but unfortunately this is not my problem. The pistons ARE now evenly extended and working well, but my caliper needs to be to the far left, which is strange.
    I had that problem in the past with a shimano hub. I put a 2mm shim inside the axle's locknut and this pushes the fork and caliper out to the left by the same amount.

    Tim

  7. #7
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    Quote Originally Posted by peanutaxis View Post
    Thanks for all that, but unfortunately this is not my problem. The pistons ARE now evenly extended and working well, but my caliper needs to be to the far left, which is strange.
    Sorry I missed that the pistons are now even. Shift the rotor inboard as I described. I've had this problem before and solved it this way.
    I can barely get my mouth around it.

  8. #8
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    Quote Originally Posted by Pedalphile View Post
    Sorry I missed that the pistons are now even. Shift the rotor inboard as I described. I've had this problem before and solved it this way.
    Oh, I see!! Yes, "realigning" it, but realigning the whole thing. Brilliant idea. Thanks!


  9. #9
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    Pedalphile great post, that should be kept as a sticky thread for 'how to fix sticky pistons'

    I would just add: sometimes even after all attempts a getting clean, aligned piston extension, you'll still have unequal extension. One trick for this:

    When you tighten down the caliper bolts, insert a piece of paper between the caliper and the pad (on whichever side is dragging) to nudge it over a bit. Then hold the lever tight, and tighten the caliper bolts like usual. For larger corrections, use a business card, or some combination through trial and error, until the caliper is centered better and no longer dragging.

    This is quicker than the hand nudge approach for the same, and will achieve the same as wombat's approach of shimming the axle over without requiring washers of different widths handy. Although, if you're already as far over as possible like OP is, Wombat's washer is necessary.
    Last edited by Procter; 12-17-2012 at 12:30 AM.

  10. #10
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    Quote Originally Posted by peanutaxis View Post
    Thanks for all that, but unfortunately this is not my problem. The pistons ARE now evenly extended and working well, but my caliper needs to be to the far left, which is strange.
    There's a million different adaptor, brake caliper, and hub combos. Sometimes you get a thicker adaptor and a hub that spaces the rotor further out to the left, when that happens you get what you see on your bike. Sometimes it's the other way around and the caliper is slammed all the way to the right to center it on the rotor.

    Personally I wouldn't worry about it as long as nothing rubs. I have the same situation on my rear brake and it's been working fine for quite some time.

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