Brake fluid is a hydraulic liquid that is critical to your vehicle’s braking system; without it, you would simply not be able to stop.
It transmits a force when you press the brake lever to the braking callipers which subsequently slows down your motorcycle.
Because the fluid resists compression in such a closed system, every amount of force you exert to the brake levers/pedal it is transferred to the end i.e. the brake pads and the brake rotors.
There are two types of braking fluid: glycol-based and silicone-based.
DOT 3, DOT 4, and DOT 5.1 are glycol-based braking fluids. DOT5 brake fluid is silicon-based. Most motorcycles use DOT4, but always check your owner’s manual for what’s been recommended by your manufacturer.
In general, the lower the number, the lower the boiling point of the fluid. Brake fluid is a liquid that cannot be compressed thus allowing the brake pads to be properly applied.
Most of us have experienced brake fade, so what is it? If you’re pushing hard on a race track or when descending a long, steep hill, the high temperatures caused by the friction of the pad on the rotor can cause the brake fluid to boil and convert into a gas.
This causes it to become compressible, making the brake lever feel spongy and reducing braking efficiency. Once the brake fluid cools, the process is reversed.
This is why it is critical to use the proper brake fluid for the driving circumstances.
Wet boiling points of brake fluids:
Glycol-based brake fluid has two drawbacks: it is hygroscopic (attracts water) and must be replaced every couple of years since it reduces braking performance when it absorbs water.
Brake fluid can also damage painted surfaces, so you need to be careful while filling up or replacing the fluid.
DOT5 brake fluid is silicone-based and has a wet boiling point of 220 degrees Celsius. It does not absorb water or damage painted surfaces.
Mixing Brake Fluids
The golden rule here is to never mix the two fluid types.
DOT 5 can be used in all brake systems specifying DOT 5 brake fluids. You should not use in brake systems that specify DOT 3, DOT 4 or DOT 5.1 fluids and never mix with DOT 3, DOT 4 or DOT 5.1 fluids.
DOT 5.1 can be mixed and used in a DOT 3, DOT 4 and DOT 5.1 braking system.
DOT 4 can be used in DOT 3 braking systems.
Being a hygroscopic fluid it’s always advisable to use a fluid bottle once and not store it for long.