Check brake fluid level and condition

Hydraulic brakes use fluid to carry the push from your lever or pedal to the caliper. The fluid sits in a small reservoir on the handlebar (front) and near the rear pedal (rear). On combined braking (CBS) bikes there may be a third reservoir. This check shows if the level is too low and if the fluid is old.

Safety

• Brake fluid strips paint and hurts eyes. Cover the tank and wear glasses when you open a cap.
• Use only the fluid type printed on the cap. Never put silicone fluid (DOT 5) into a system made for DOT 3, DOT 4 or DOT 5.1, and never put engine oil or water in a brake system.

You need

• A clean rag.
• A sealed, new bottle of the correct fluid if you need to top up. Fluid takes in water from the air once the bottle is open, so do not use a bottle that has been open a long time.

Steps

1. Stand the bike upright on level ground. Turn the handlebar so the front reservoir is level.
2. Look at the window or the translucent body of each reservoir. The fluid must be above the LOWER mark.
3. Look at the colour. New fluid is clear to light yellow. Dark brown or cloudy fluid has taken in water and dirt and should be replaced with Replace brake fluid and bleed the brakes.
4. If the level is low, first ask why. As pads wear, the pistons move out and the level drops slowly; that is normal. A fast drop means a leak. Check pads with Check brake pad wear and look for leaks with Check brake hoses and banjo bolts.
5. To top up, clean the cap, then open it. Do not let dirt or water fall in.
6. Add fluid to the UPPER mark only. If you are going to fit new pads soon, the level will rise when you push the pistons back.
7. Refit the diaphragm (rubber seal) and cap. K-Light 125: front cap has two screws; rear cap is screwed on by hand until it just seats, then turned a further 1/6 turn.
8. On a K-Light 125 or other CBS bike, check the CBS reservoir as well.
9. Wipe any spilt fluid at once with a wet rag.

Check your work

• All reservoirs are between the marks with the bike upright.
• Caps are tight and nothing leaks when you pull the lever and press the pedal.
• If you do not know what fluid is already in the system, do not top up with a different brand. The K-Light 125 manual says to replace all of it, then use one type and brand only.

If it did not fix the problem

• Level keeps falling: Brake fluid is leaking.
• Lever soft even with the level correct: Brake lever or pedal feels spongy.

Reference values (K-Light 125)