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.