How to bleed Mtb Brakes
How to bleed MTB brakes
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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 wood, 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.
