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  1. #1
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    XT piston - can't reset

    I probably let my brake pads wear too much. Anyhow, I am trying to push the pistons back into the calipers. The left is OK but the right won't move. I have tried Park's and others' instructions to open the reservoir port and use a plastic tire lever, but no joy. Anything else I can try? Thanks.

  2. #2
    tlg
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    Do you have crud on your piston's like this? It could be preventing them from pushing back in. And damage the seals if you do.
    If it's not too bad, you can clean them with a Q-tip and some alcohol. But if really bad you may have to remove the pistons.

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  3. #3
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    Are they 785s? I had two calipers do this, and both times it turned out to be a cracked piston. There are rebuild kits out there, but they're not "officially" rebuildable, if I recall correctly.

    Shimano warrantied the one that I remembered to send in. They sent me a new M8000 caliper as a replacement.

    But like was said, it could also just be a buildup of gunk around the piston/seal. Be careful though. The ceramic pistons - assuming that's what you have - are pretty fragile.

  4. #4
    'brifter' is a lame word.
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    Don't push directly on the piston, leave the old pads in and use whatever tool you're using on them, especially if they're the newer ceramic pistons.
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  5. #5
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    Also, if the piston is way out (due to totally worn out pads) they can be tricky sometimes to push back in. You have to push them nice and straight back in and being way out they have less piston inside the bore guiding it. Work it a little all the way around and around to get it started. If you push hard in one spot you can get it bound up crooked.
    Agree, clean it with Q-tip first as well.
    Good luck and take your time. Do not force it. It is kind of a developed feel thing.

  6. #6
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    They make ceramic pistons for these brakes now? What is wrong with stainless steel? and why use ceramac?

  7. #7
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    Quote Originally Posted by aclinjury View Post
    They make ceramic pistons for these brakes now? What is wrong with stainless steel? and why use ceramac?
    Thermal properties perhaps?
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  8. #8
    tlg
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    Quote Originally Posted by aclinjury View Post
    They make ceramic pistons for these brakes now? What is wrong with stainless steel? and why use ceramac?
    Yes, for quite a while now. Heat management to prevent hydraulic oil from boiling.
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  9. #9
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    Quote Originally Posted by tlg View Post
    Yes, for quite a while now. Heat management to prevent hydraulic oil from boiling.
    That makes sense to protect he liquid from boiling. But now the heat would have to go somewhere, and that would be the pads and the disc. I haven't used disc on the road, but in the mtb world. I don't believe liquid boiling over was/is ever an issue, or was there?

  10. #10
    tlg
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    Quote Originally Posted by aclinjury View Post
    That makes sense to protect he liquid from boiling. But now the heat would have to go somewhere, and that would be the pads and the disc.
    The pads and rotors have heat fins. Personally, I use regular pads and rotors. I don't have long descents that I have to worry about.



    I haven't used disc on the road, but in the mtb world. I don't believe liquid boiling over was/is ever an issue, or was there?
    Oh heck yea. Always been an issue.

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