In this video we're going to show you how to bleed a Shimano hydraulic disc brake.
In this instance, we're using one of their lower-level group sets,
but the principle remains the same throughout the Shimano range and also for
the majority of other manufacturers. This is one of those jobs which can seem quite
daunting to the majority of people. When you know what you're doing,
it is relatively simple. Why would you want to do it? Well, if you're getting
reduced braking performance, well, the action of the lever here feels quite
spongy, it might well be you've got some air inside the braking hose here,
and that's when you need to bleed the brakes. But of course, the most important
function of your bike is the braking, so if you're not 100% confident in what
you're doing, we would recommend taking it to a professional bike mechanic.
For this job, you'll simply need a set of Allen keys plus the correct Shimano brake
bleeding kit. Before you start, try to make sure that everything is as clean as
possible. Then you need to get the bleed point of the caliper at the lowest point
of the system so that any trapped air moves upwards. Next use your Allen key to
loosen the brake lever and move it upwards 'til it is roughly level.
Undo the small Allen key bolt on top of the lever, making sure that you keep the
little O ring safe. Then screw in your Shimano bleed pump. Just lightly by hand,
making sure that you don't over-tighten it. Going down to the caliper now,
take off the dust cap. At this point, you might want to remove the wheel to make it
easier to access the brake, but there is no need to on our model.
Take your bleed syringe and fill it with the Shimano hydraulic mineral oil.
Then undo the valve, using your three millimeter Allen key, just one turn
anticlockwise. Put gentle pressure on the syringe and start pumping the fluid
through the cable. You'll see the old fluid appear in the reservoir on top of
the brake lever. As you do it, give the cable a flick to get rid of any air
bubbles. Once the reservoir is almost full, firstly tighten up the valve on the
caliper, then place the provided bung into the reservoir, plug the hole,
then unscrew the reservoir from the lever. Dispose of the old fluid safely,
and then replace the dust cap on the lever. Then back down on the caliper,
pull the hose locking device away and then the hose itself, making sure not to spill
any fluid. Give the whole area a clean and then replace the dust cap on the caliper.
Repeat the same steps for the other brake, again making sure that the bleed point is
the lowest area of the system. On our stand, we can get the bike into the right
position, but if you don't have that luxury, then you may need to remove the
brake caliper from the frame. For more videos like this, subscribe to GCN.
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