Why it ages
Most brake fluids absorb water from the air. Water lowers the boiling point of the fluid, so under heavy braking it can form vapour bubbles and the lever feels soft.
Checking the level and colour
- Look at the reservoir with the bike upright and the bars straight. The level should be between the marks.
- Fresh fluid is clear or light amber. Dark or cloudy fluid needs to be replaced.
- A level that drops quickly can mean worn pads or a leak. Have it checked.
How often
Many manufacturers recommend replacing the fluid about every two years, whatever the mileage. Follow the interval in your owner’s manual.
Use the right type
Use only the grade written on the reservoir cap or in the manual, such as DOT 4. Do not mix different types unless the manual allows it, and never use an opened bottle that has been stored for a long time.
Warning signs
- A spongy lever or a lever that goes closer to the grip than usual.
- Brakes that fade after long descents.
- Fluid on the caliper, hose or master cylinder.
Brake fluid damages paint and is harmful to the skin and eyes. Because the brakes are a safety system, have the fluid changed and bled by a qualified mechanic unless you are experienced. See brake care.