Motorcycle Glossary

Brake fluid

In Turkish: Fren hidroliği

In short

Brake fluid is the high-boiling-point fluid that carries pressure from the master cylinder to the caliper.

The most common types on motorcycles are glycol-based DOT 3, DOT 4 and DOT 5.1; use the type printed on the reservoir cap. Silicone-based DOT 5 must not be mixed with them.

Glycol-based fluid absorbs moisture from the air (it is hygroscopic); as moisture builds up the boiling point drops and the brakes can fade under hard use. That is why it is usually changed every 2 years regardless of mileage.
Dark, brown fluid is due for replacement.
Brake fluid damages paint and plastics; wash any spills off immediately with plenty of water.