Viewing 11 posts - 1 through 11 (of 11 total)
  • Shimano brakes ‘weep port’ i had no idea
  • howsyourdad1
    Free Member

    Cleaning a sticky piston tonight, pressed the calipers back in and ‘pssst’ some oik shot out of what is apparently a ‘weep port’.

    https://bicycles.stackexchange.com/questions/69356/what-and-where-is-the-weeping-port-on-shimano-mtb-brake-levers

    What is this wizardry? Brakes seems fine though after a quick bleed at the lever. Or will i die tomorrow on my epic descent?

    footflaps
    Full Member

    Is that new, pretty sure my 10 yr old XTRs don’t have that….

    sillyoldman
    Full Member

    Sounds like the system was overfilled and you’ve damaged the diaphragm pushing the pistons home as there’s too much fluid for the reservoir to contain.

    Used to mean a new lever needed, but Shimano have started supplying spare diaphragms for warranty use. Not sure if the UK have them yet though. Worth getting your LBS to ask Madison.

    They’ll need to know model no and LH/RH as they’re asymmetric and different for servowave vs non-servowave levers.

    Alternatively, find a pal with a dead lever (but with ok diaphragm) and use it as a donor for the diaphragm.

    Kuco
    Full Member

    You can get a diaphragm for the rod levers as I needed a new one on my Ultegra lever a couple of weeks ago.

    howsyourdad1
    Free Member

    Thanks. I’m not in the uk however. I have an old spare xt lever so could just swap the whole thing, or borrow a deore one from the other bike.

    It really does seem fine though… i’ve checked for seepage, nothing, brake works and feels solid. .

    endoverend
    Full Member

    Yes, got a surprise when mine did that too. Mine did it a long time ago, I didn’t replace the diaphragm and it did not change the performance at all, so had forgotten about it. I remember looking into it and deciding the diaphragm is fairly thick where it would have to split to do this, came to the conclusion that maybe fluid gets around the edges before being ejected…I may be completely wrong in this regard so curious to know what the correct technical answer is, is it a feature? If I hadn’t witnessed the spurt I’d have never known it happened from the after-effects and feel no need to chase it. So maybe try them for a while and see what happens…

    walleater
    Full Member

    It’s a breather hole to allow the bladder to easily expand when fluid is hot. You’ll see it on plenty of brakes, some more obvious than others. Often just a little random looking pin-hole. Fluid can come out of there if fluid gets in between the outside of the bladder and the inside lever body / reservoir cover, or if the bladder splits, which seems to be really common with current Shimano brakes.

    endoverend
    Full Member

    I’m assuming if the bladder/ diaphragm splits then they would continue seeping fluid past that end port, though I guess once the lever closes off the reservoir port that it’s not under all that much pressure, so maybe there’s more to it. Others in that link above seem to show a countinued leaking from that port afterwards and inability to hold fluid in the reservoir. Whereas mine showed no signs of leaking after she spurted…and appear to be happy.

    argee
    Full Member

    As explained, it’s just a weep port if the system heats up and oil expands, or it’s overfilled and gets behind the diaphragm.

    Had it a few times over the years, easy enough fix if you want to clean inside, but it does involve removing the lever blade, removing the little grub screw holding the diaphragm in and then putting it back together again, which can be painful!

    chrisyork
    Full Member

    As walleater said, if you watch some GMBN videos on YouTube about disk brakes they tell you all about it but yes to allow tiny bits of air to escape to keep the system working optimal. Said better than that by walleater

    dyna-ti
    Full Member

    From experience, they appear to have more than one ‘weep port’.

Viewing 11 posts - 1 through 11 (of 11 total)

You must be logged in to reply to this topic.

Thanks for popping by - why not stay a while?IT'S FREE

Sign up as a Singletrack Member and you can leave comments on stories, use the classified ads, and post in our forums, do quizzes and more.

Join us, join in, it’s free, and fun.