Blog - How to bleed the brakes on a Motorcycle

How to bleed the brakes on a Motorcycle

Published by PowerSports MotoUsher

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Suffering from spongy soft brakes? Bleeding / Purging the brakes is not a difficult task. In fact we are going to be sharing a couple of good videos done by other riders on how to bleed the brakes as well but we will be talking about the mechanism as well in a non geeky way.

Important points to know

DOT 4 brake fluid is corrosive. Clean it immediately when it spills on metal. Wash (water soluble) it once you are done. It needs to be disposed accordingly as well.
DOT 4 brake fluids have an expiration date. You will need to change it and they absorb moisture so you ideally should dispose off older opened bottles.
Please only use the recommended brake fluids by your company. DOT 3/4 whatever is suggested.

This is what we are going to cover:

What is brake bleeding? Why is it necessary ?
The mechanism of brake fluid bleeding
How to bleed the brakes.
Devices to ease brake bleeding process.

What is break bleeding? Why is it necessary ?

Break bleeding is the process of removing ( purging ) air bubbles from the hydraulic brake lines. The brake system has hydraulic fluid inside which does not work well with air bubbles. This is because air bubbles compress whereas the fluid doesn’t (incompressible) . You would want the pressure of the brakes to easily transverse through to the brake pads right? The air presence in the system decreases its functionality and so we need to purge them out for a safer ride.

Some terms used:

The master cylinder is the reservoir where the fluid is housed.
The bleed valve is the valve on the break calipers where the air and fluid comes out from. They are designed accordingly. (So whenever you bleed or have made some modifications make sure that the stock orientation is maintained).

Mechanism of air bleeding.

The idea is that you compress the the fluid and the air (forcing clean the system) and then release the fluid and air while in compressed state. To get a bubble-free brake fluid in the system the break line needs to be free from kinks and twists for the mechanism to work. The air bubbles need to be force cleaned towards the exit point; the bleed valve. In terms of the motorcycle you press the brakes to compress the air. Then you open the bleed valve to let the air and fluid out. Then close the bleed valve shut before you leave the pumped brake or air will be sucked in from the valve rather than fluid from the master cylinder.

Here is a good website to know more in details and one with bleeder valve that explains it well too

How to bleed brakes?

We are going to start with a simple pump and hold method. Later we shall suggest possible ideas which are practically executable in India.

Setup required:

Ring spanner to open bleed valve
Screw ( or philips ) driver to open the master cylinder. Keep this open till the task is completed
Cloth piece to wipe the fluids clean
A clear tube to fix to the bleed valve to see the air bubbles escaping the b
A can or something to collect the brake fluid
Brake fluid

Pump and Hold Method with two people or may be even one by bending over the motorcycle :

Pumps the brake pedal to compress the air, then hold the pressure till next step.
Open the bleeder valve to let out fluid and air, then close the valve
Release the pump after the valve has been closed or air will be sucked in rather than the fluid
Repeat the process
Replenish the master cylinder reservoir before it goes below the minimum level or the process will have to be repeated and never go above the maximum level or the brakes will get locked.
Make sure you don’t bottom out the brakes. keep something under them.
A block may be placed under the pedal so that it does not bottom out during this procedure