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  1. #1
    mtbr member
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    Stuck Piston - Formula RX

    I have a stuck piston in my rear caliper. I'm sure it's just gunky. Any advice on what is the best method to clean it and get it moving again? ( I really don't want to have to bleed them. )

    At the moment I have it set up like a cheap mechanical disc, not ideal....

  2. #2
    fliernh
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    Have not had a stuck piston on my Formula brakes but have had on my Maguras. The solution was to push both pistons back in all the way. Then hold one in and actuate the brakes letting the other piston come out (but not too far). Clean it with q tip and alcohol, push the piston back in and repeat for the other side. Push both back in and put back together and actuate to see if it works. This firmed up the lever considerably. Feels like it needs bleeding but if it is a stuck piston, it just needs to be broken free.

    Hope that helps.
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  3. #3
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    Thanks, I'll give that a try!

  4. #4
    fliernh
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    Suggest using a flat wrench (like a cone wrench) in between the pistons. It gives you leverage to push them back and keeps a piston from going out to far ( which would be bad). If you didn't need to clean the pistons, it can be done in place by pushing on the rotor to move one piston in while having someone actuate the lever repeatedly to cycle the other piston out. Works on the trail when brake suddenly goes soft but no leakage. Wear glove to touch rotor.
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  5. #5
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    You may want to put a couple drops of brake fluid on the piston after you the clean it before you push it back in.

  6. #6
    fliernh
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    Quote Originally Posted by rlouder View Post
    You may want to put a couple drops of brake fluid on the piston after you the clean it before you push it back in.
    Good idea!
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  7. #7
    Rope stretcher
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    I have also had good luck with cleaning w/ qtip dipped in isopropyl alchohol and lubing with qtip dipped in dot 4 brake fluid. I usually repeat several times cycling the pistons in and out a few times and wiping the grime off each time. Be careful not to push the pistons out too far! I recently had a really sticky piston which was difficult to get out. I was able to coax out by holding the opposite piston in w/ the handle of a cone wrench while pulling the lever.

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