How to Bleed Shimano Disc Brakes – Mountain Bike Maintenance

How to Bleed Shimano Disc Brakes – Mountain Bike Maintenance


There are some occasions where you’re
going to need to bleed your brakes. Maybe you’ve changed the hose and
shortened it, sometimes your brakes start to feel spongy, or just a bit
of annual maintenance. So this is how to bleed a Shimano brake. You will need brake fluid, mineral oil for
Shimano brakes, other brands use DOT 4 or 5.1 oil. Make sure you get the right
stuff, otherwise you’re going to mess up your seals. A Shimano bleeding kit, which
is a funnel and a syringe, a brake block, a 7mm spanner, some
Allen keys, some brake-cleaning fluid or similar solvent, and a rag. First thing I’m going to do before I even
start bleeding the brake is give the hose a quick check-over, just visually check
there’s no holes in it or anything like that that’s going to let in any air into
the system, and check the connectors at the brake lever and down at the caliper
are nice and tight. Adjust this brake lever to about 45 degrees on the
handlebars. Then I’m going to make sure this free stroke is wound all the way in
clockwise, which mine is, because I like there to be minimal
movement on the brake lever. So now I’m going to remove the pads from
the caliper. First thing you need to do is remove that clip from the pin, put that
somewhere safe. Then I’m going to need a little flat-blade screwdriver, just to
remove the pin that holds the pads into the caliper. Once you’ve got that pin out,
the pads should just come out of the top of the caliper like that. Okay, so now you want to gently push these
pistons back into the caliper. Use something soft like a Tuff tire lever
or something like that, don’t really want to use a metal
screwdriver or anything like that, as it can damage the
pistons and the caliper. If when you’re trying to push these
pistons back into the caliper, you’re pushing one in, but it’s then
pushing the other piston back out, you’re going to have to forget about this
for one second and go up to the lever and move on to the next step, and
come back to that caliper. So I’m up to the brake lever and I’m going
to remove this bleed screw using a 2mml Allen key, just when you remove that, be
careful to make sure you get that tiny little o-ring and place that somewhere
safe. Now I’m going to attach the funnel of the Shimano bleed kit, make sure you
don’t cross-thread this, because they’re quite delicate little
plastic threads. So now I’m going to go back down to the
caliper, and those pistons should now push it back into the caliper a little bit
easier, because it’s going to let some oil out and into this funnel. Now I’ve got the pistons pushed back into
the caliper. I’ve fit this bleed block to the caliper, and just secure it using
the pin that you used to keep your brake pads in. Okay, so now we’re ready to start
bleeding. I know some people like to take that caliper off the bike so that you can
get it directly underneath the brake lever, so if you are trying to do the rear
one, you might want to tip the bike up, just to get the caliper a little bit lower
than the brake lever. Okay, so half-fill the syringe with
mineral oil. Once it’s about half-full, tip that up so you’ve got that bubble,
comes right up to the hose, and just try and push that air out of the
syringe, and the hose is completely full of oil, no bubbles. Okay, so I’m going to remove that little
rubber boot that’s on your bleed nipple. When I’m attaching this hose to the bleed
nipple, I’m pushing on it ever so slightly, so that I don’t get
any air bubbles in that hose as it goes over and onto that nipple. So using your 7mm spanner, just give
that an eighth of a turn, so that opens up. So now I’m pushing gently on the syringe,
pushing fluid through the hose, and it’ll come up through the system and
into my funnel up at the brake lever. When the oil goes black like that, the
performance of your brake isn’t brilliant, so try and flush the new fluid through,
maybe two or three times a year. But the idea is just to flush fluid all
the way through, so that it’s pushing all the bubbles out of the top and into this
funnel. So keep pushing on the syringe until no bubbles come through and into
this funnel. If, like me, this funnel’s almost full, and my oil’s
still black, I’m just going to tighten up the bleed nipple on the caliper
with my 7mm. Okay, so my bleed nipple’s tight on the
caliper. I’m just going to use this plunger in the funnel, just to plug that
up, so I can then remove the funnel from my bike without dropping any oil, and I’m
just going to dump this oil. This is black, used oil, so it’s no good
to me. So get rid of that somewhere safe. So I’ve reattached the funnel, pulled out
the plunger, and I’m going to stick some more fresh oil in the
syringe and go again. So I’ve pushed all that fluid up and
through, you can see there’s some fresh fluid coming out of the brake lever and
into the funnel now, some nice orange or pinky color like it’s coming out of the
syringe, and also I keep pushing until there’s no more bubbles coming out of that
brake lever. If they’re still coming out sporadically, you can start just tapping
the hose a little bit with your little spanner, just to free up any air bubbles
and get them loose and get them traveling up and into this funnel. And keep going
until there’s just fluid coming out and no more air bubbles. Okay, so just tighten that bleed nipple,
and then we’re finished with the syringe, so take that off and just give that a
quick wipe, just to get rid of any overspill of oil, just for now. Just give your brake lever a feel now,
should be feeling nice and firm if you’ve got rid of that air out of the system. So a little pro tip here, just to make
sure you’ve got all the air out of the caliper, is to attach the hose, and if you
use something to collect the oil, I’m using a rubber glove so it looks good,
and I’m going to use my 7mm again, and I’m going to pull the brake on now, so
I’m putting a bit of pressure into the system, and I’m just going to undo this
nipple an eighth of a turn, and then quickly tighten it back up, so
I’m just really quickly letting a little bit of oil come out. So if there is any
air in this caliper, it’s just going to pop out. Just make sure you tighten it
back up nice and quick. So as I’ve just undone the caliper bolt a
couple of times, really quickly, to let oil fire out of there, and any air
bubbles, I’m just checking that the oil level isn’t dropping too low in this
funnel. If you let it drop, it’s going to let air come into that
system from above, so keep plenty of oil in there. My lever is now feeling really
nice and firm, so I’m pretty sure I’ve got all the air out of the system. Okay, so the bleed nipple’s tight on the
caliper now, I’m coming back up to the lever, and I’m just going to undo the bolt
and just move the lever around, so bring it up level, or even a little bit
higher than level, and we’re just trying now to pump the brake lever a few
different angles, try and get any air that’s still stuck in this master cylinder
out and up through the funnel. So give it a little bit of a tap as well,
and any air bubbles should then be released. So with it flat, I’m pumping on
the brake lever, nothing’s coming out, I’m going to drop it a little bit, again
making sure that the hole at the bottom of the funnel is always covered up with oil,
so no air can drop into the system. A few more times, and I reckon I’m good to
go. So all the air is out of that system, the brake’s feeling nice and firm. I’m
just going to do that back up on the handlebars. And I can use the plunger
again, just stick that into the funnel so no oil drops out, and then remove the
funnel from the brake lever. So just before you put that bleed nipple
back on, you might want to put a couple of drops of fluid just in
the top to top it back up. Then screw that bleed nipple back in. We have a rag to catch any oil, and then
use a bit of this solvent again, just to get rid of any oil on the caliper.
I’ll make really sure I’m doing that, because you don’t want any oil to get onto
your brake pads when you’ve replaced them. You can stick your little rubber
cover onto that nipple, stop any dirt getting on there. So, pads back in. So, your Shimano have an
R and an L for right and left, so get them correct. Also make sure you’re
not getting your oily fingers all over the braking surface, just slide those back
into the caliper. Put your pin back in and remember the clip on the end. So front wheel’s back in, and just give
that lever a few pulls. It might feel a little bit different, as
it’s just pushing the pistons back in towards the brake disc, but now I’ve done
that, it feels really nice and consistent and I know that I’ve done a really good
bleed of this brake. Quite often you don’t need to do a whole bleed like I’ve just
done, you can just attach the funnel and drop a bit of oil in there and just give
that lever a bit of a pump. Often the air rises up and into this front
brake lever or your back brake lever, but it rises up the system, so it sits
just in the top here. So it’s using that funnel as a really quick, easy way of just
giving the brake a flick-over, and getting the air right and just
dropping a little more oil in. If that doesn’t work, this full bleed,
like I’ve just done, should really just do the trick. So once that’s done, you might need to
center your caliper again, to get that disc spinning nicely in the
center, and just reset your brake lever how you had it before, the reach
and the free stroke. So there you go, there’s how to bleed your
disc brake. It’s not the nicest of jobs, it’s a little bit messy, but it’s actually
quite easy to do, so have a go. If you want to see more videos from GMBN,
you can click up here for how to check your disc brakes, or click down here for
how to how to brake like a pro. Or click on me and my fresh new oil to
subscribe to GMBN.