I have a shimano XT hydraulic disc brake system. While servicing it I took out the pads an checked the pistons in the caliper and noticed that only one is extracting. After a few pulls on the lever when the one piston reached the end of its travel, the brake fluid spurted from it. I've since resettled and reset the pistons but I'm thinking I might still have fluid leaking out from there in the future. Or maybe that was normal behavior?

1 Answer 1


That is normal behaviour. You pushed the piston way out, so oil from behind it found a way out.

General actions suitable for your case as well:

  1. remove wheel
  2. remove pads
  3. carefully push the lever a couple of times in order for the pistons to extend a couple of mms. if one is stuck, make sure you push the other one with a plastic tyre lever while pulling the brake lever in order to make the sticky piston extend.
  4. clean sides of piston with earbud with alcohol. clean again with paper. this ensures free movement of pistons later on.
  5. carefully fully push pistons back into their place with a plastic tyre lever. this is called "reset".
  6. insert shimano yellow block
  7. do a full bleed
  8. remove block
  9. install pads
  10. install wheel
  11. go ride

Also, make sure that no oil was spiled on pads or disk. If so, replace pads and clean disk very well.

  • And also, be careful next time. You should never press the levers on a hydraulic system without pads AND without the caliper being in a disc or having something separating the pads, precisely to avoid this from happening.
    – super
    May 27, 2015 at 20:19
  • @super: you should, but carefully. See step 3.
    – cherouvim
    May 27, 2015 at 20:25
  • But can't you check for sticky pistons with the pads and a disc? Or at with then pads and a plastic separator, something like this: championunited.com/home/sites/default/files/images/… That is what I usually do, and seems much safer.
    – super
    May 27, 2015 at 20:28
  • In order to check and clean (fix) sticky pistons you need to have nothing between the pistons. That's because you need easy access for cleaning and to perform a couple of full extensions and resets.
    – cherouvim
    May 27, 2015 at 20:31
  • Ok, I got you. You're right 👍
    – super
    May 27, 2015 at 20:52

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