I have a problem bleeding Shimano XT brakes: The oil can come down if I open the system at the bottom, and the oil drips down. But once I connect the syringe, put the little plastic cup screws on the top, then I cannot pump the oil toward the top. I have done several tests, tried to undo the bleeding screw at the bottom on the caliper of increasing turns (1/4, 1/2, 3/4...until the oil comes out from the screw sides (too unscrewed). I have as well tried using a différend bleeding screw, and the oil pass through nicely. I have opened and cleaned the master cylinder at the lever, so I know all is good. All I can think is it is a hose and oil/pin problem. What do you think? Ever seen anything like this? I should mention that I have worked as a bike mechanic for the past few years... Thanks Paolo

  • please post a photo of the caliper and/or the model number (eg BR-M785)
    – Noise
    Commented Jan 23, 2022 at 20:31
  • Sorry Joe, how do I post a picture? Commented Jan 24, 2022 at 22:00
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    You can post a picture by clicking edit and then clicking the picture icon to upload, or while editing by pressing Ctrl+G
    – Swifty
    Commented Jan 25, 2022 at 22:06

1 Answer 1


The lever reservoir has a tiny hole to let fluid and air pass in/out of the system. This hole gets closed off by the master piston when the lever is pulled.

I've seen similar behaviour to yours once before when the brake had been reassembled (reach was too tight or too loose I forget), such that the master piston was out of place and the breather hole was closed off, preventing me from pushing fluid up from the caliper end. Fluid seemed to flow down ok but that was probably merely residual in the hose. I experienced the same problem as you describe and tried the same steps focusing on the caliper end first before realising what had happened. Bike owner confirmed messing with the lever before having initial problem.

Caveat: this was on a cheaper/simpler brake, BL-M315 and the reach adjustment on yours might not have the same effect, but I would try resetting the reach adjust to see if it has an effect.


  • Thanks, this is actually an interesting and helpful comment. Thank you Commented Jan 24, 2022 at 21:59
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    You're welcome, worth looking into if only to rule it out but your clear write up sounded like a familiar tale. presumably it's one of your fleet bikes and anyone could have messed with it without telling you the full story..!
    – Swifty
    Commented Jan 25, 2022 at 22:04
  • Unfortunately I had bought the brake set 2nd hand to put on my hardtail, but clearly this did not happen since the brake did not work, did not have enough oil and was impossible to bleed. Commented Jan 26, 2022 at 21:02
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    I am going to try and fix it next days. Thanks for your suggestion. Commented Jan 26, 2022 at 21:02

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