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A couple of weeks ago, I tried to bleed for the first time my Shimano disc brake. I won't say it was easy and I'm not sure I did it perfectly but the fact it brakes better now.

However, I've noticed this morning that some mineral oil is leaking from the bleed nipple of the caliper. I noticed that I'd lost the cap. I also checked the bleed screw was correctly closed which is the case.

Is the bleed nipple cap essential and should I get a new one to avoid further leak? Would it be possible the leak have another origin?

For information, my caliper is a Shimano SM-MA-F180P/P2.

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    Just in case, Shimano SM-MA-F180P is a caliper mount adapter, not the caliper itself. Nov 13, 2021 at 11:39
  • How much is leaking? A finite little bit is normal after a bleed; there could be a little excess oil remaining after the bleed screw.
    – MaplePanda
    Nov 13, 2021 at 17:44
  • @MaplePanda Not so much but enough to make me noticing using the quality of my brakes.
    – Pierre
    Nov 13, 2021 at 18:18

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The cap only keeps the bleed nipple clean. It doesn't constrain any pressure or prevent leaks per se. Its absence could cause a leak in some sense by allowing dirt to contaminate the bleed port seal when it's opened.

The bleed port hardware is replaceable on many Shimano calipers. If you're losing fluid there, that's the thing to try and it will likely work. To figure out what you need, google up the "ev" (exploded view) document for your caliper model to find the applicable part number. They usually come as an o-ring and bleed screw together in a kit.

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