bicycle repair Tip How to bleed MTB brakes > Bicycle Repair Tips

 

According to a poll I put up on the YouTube
community section last week, 32% of you bleed
your own brakes.
21% of you have a shop bleed your brakes,
and I can’t blame you.
There’s no shortage of reasons to let someone
else do it, especially if you live in an apartment.
As for the remaining 46% of you it’s not
about the know-how, the tools, or the mess.
You just don’t know what the freak a brake
bleed is, plain and simple.
This is okay because today, that’s gonna
change.
Even today’s most basic mountain bikes have
disc brakes.
Some use cables, while others use hoses filled
with oil.
Hydraulic brakes are powerful and accurate,
which is why cars and motorcycles have utilized
them for the better part of a century.
The hydraulic brakes on a bike consist of
a lever, a hose, and a caliper.
This closed system is filled with oil, so
when you pull your lever the oil is displaced,
forcing the pistons in your caliper to squeeze
your rotor.
But why are these systems filled with oil?
Why not a gas like air?
Well air compresses easily, which is why it’s
ideal for suspension forks.
Filling a fork with air ensures it will move
when you hit a bump.
But if we were to fill your fork’s air chamber
with oil or some other liquid, it would feel
completely rigid.
As for cable actuated brakes they work fine,
but there’s friction between the cable and
the housing, in addition to some bending and
stretching.
This results in energy loss that hydraulic
systems are able to overcome.
But hydraulic brakes are prone to wear and
contamination.
Air can make its way around the seals, and
become part of the system.
Air in the system makes the lever feel spongy,
and reduces the effectiveness of the brakes.
A brake service can involve flushing the system
and replacing old oil, but more often it just
involves getting the air bubbles out.
This process is called a bleed, but why?
Why not a fart?
We are, after all, trying to get the air out.
Good question.
The term originated in auto shops, where some
procedures involve letting a bit of oil drip
from the caliper, hence the term “bleed”.
But on a bike, the procedure can vary greatly
depending on the brand and model.
Each model of brake requires a different set
of tools, different oil, and a unique set
of steps.
This is why most manufacturers include detailed
tutorials on their YouTube channels.
Detailed as they are, these tutorials assume
a base level of understanding that a bike
mechanic or enthusiast would have.
Otherwise, you don’t know what the freak
they’re talking about.
Today that’s gonna change.
We’re gonna build a transparent model so
you can see how a bleed works.
The system uses a lever and caliper made from
syringes, connected together with clear aquarium
tubing.
I even cut this trigger out of d, which
as it happens, looks like a nose.
At the end of each syringe is a fitting, which
includes a bleed port that we can cap off.
This is far from a perfect representation
of a hydraulic disc brake, as it’s not sealed
very well, only has one piston, and is filled
with vegetable oil.
But pull the nose and the caliper moves.
As you can see, there’s a fair bit of air
in this system.
This calls for a bleed.
To perform a bleed on any brake system you
need a bleed kit.
Mine contains oil, two syringes, and a bleed
block.
First we’ll install the bleed block to keep
the piston from moving.
This will ensure we end up with the right
amount of fluid in the system.
Next we’ll fill our syringe with brake oil,
and take care to get all the air out by turning
it upside down and letting the bubbles rise
towards the opening.
This is also an important step in a real bleed
since you don’t want to pump more air into
your brake system.
To connect the syringe we’ll open the bleed
port at the bottom.
Notice how it doesn’t leak all that much.
The same thing happens if you fill a straw
with water.
If you open one end the liquid pretty much
stays put.
But if you open both ends it comes pouring
out.
The same is true for a hydraulic brake system.
Only open one end at a time.
Once we have our syringe connected, we can
open the bleed port up top and connect another
syringe to collect the excess fluid.
Now we’ll pump oil up from the bottom through
the system.
The excess oil flows into the syringe at the
top, and so does a fair bit of air.
You can see how pulling up on the top syringe
creates negative pressure and forces bubbles
out of nooks and crannies.
Pulling the lever also forces bubbles out
of the system.
Theoretically we could remove the lever or
caliper from the bike and tilt it in different
directions to let trapped air flow upwards.
Positioning also matters on real bikes for
more reasons than one.
When we’re satisfied, we can close up the
system one end at a time, and remove the bleed
block.
Now our brakes are working.
There’s not a big difference because this
system wasn’t very refined in the first
place.
Like our model, real hydraulic brakes have
bleed ports.
They do tend to have nooks and crannies that
can trap air.
And, pulling the lever is usually a step in
real brake bleed procedures.
To bleed my Magura MT5’s, the process is
actually very similar to our model.
You pump fluid from the bottom to the top,
flick the lever, and bubbles come out.
There are quite a few other steps, but they’re
easy to understand.
For instance you need to remove the wheel
and brake pads to prevent them from getting
contaminated with oil.
And like our model, bleed blocks are installed
to keep the pistons located.
Also our model used vegetable oil, while my
MT5s use a mineral oil blend from Magura.
On shimano brakes you pour oil into this funnel
to displace air.
On some Hope brakes, you take the whole top
of the lever off and fill it up.
In every case, there’s a specific kind of
oil, and tool set required to complete the
process.
So, if you want to try bleeding your own brakes,
here are the steps.
Step 1.
Order a bleed kit specific to your brake model.
There’s this special online tool you can
use to find this called Google.
The bleed kit will come with everything you
need including the right oil for your brakes.
When you run out, you only need to order more
oil, as the rest of the stuff in the bleed
kit will be reusable.
Step 2.
Get some additional supplies.
Rubber gloves would be first on the list since
brake oil is nasty, and you want clean hands
to reinstall your pads with.
Rags are also useful, along with a spray bottle
filled with water or alcohol.
For any bleed you’ll also need basic shop
tools but if you’re bleeding your own brakes
I assume you’ve already accumulated some
torx and hex wrenches.
So on to step 3.
Find a tutorial specific to your brakes.
Most manufacturers have these, but I’d actually
steer you towards the ones done by shops,
and my friends at Global Mountain Bike Network.
These tutorials might seem overly detailed
at first, but now that you know the basics
I think they’ll make more sense.
Watch your tutorial over a few times, and
make a cheat sheet of the steps if necessary.
Finally step 4.
Attempt to bleed your brakes.
You’re gonna spill some brake fluid on the
floor, and probably fumble with the bleed
screw.
You might even screw the entire process up
and need to start over.
But once you learn how to bleed your brakes,
you’ll find that it’s easy to do.
Even better, you now know your system through
and through.
If the oil is old and discolored, you can
do a flush and refill using pretty much the
same steps as a bleed.
Still some of you might be thinking, “this
looks kind of messy”.
I’d rather pay a shop to do this.
That’s perfectly fine, and the good news
is that it’s not expensive.
Even a complete flush and bleed on your front
and rear brakes will be less than $50, and
a quick touch up can be way less than that.
So the next time you get that spongy feeling
in your levers, you know what the freak to
do.
Bleed your brakes, or have a shop do it for
you.
I hope you found this video useful or at least
entertaining.
If you did, please give it a thumbs up and
share it with someone who would find it useful.
If you want me to do more overview videos
like this on other maintenance procedures,
let me know in the comments.
If you’re ready to try bleeding your own
brakes, I also left some resources in the
description.
Thanks for riding with me today, and I’ll
see you next time.