Repair

Brake bleed

Replacing the fluid in a hydraulic brake and pushing out the air bubbles that make the lever soft. Once a year, or whenever the lever feels spongy or pulls to the bar.

Also known as: bleeding brakes, how to bleed brakes, brake bleeding

Key facts

Skill level
3/5
Time
45 min
How often
once a year, or when the lever feels spongy
Tools
bleed kit for your brake, bleed block, Torx and hex keys, nitrile gloves, rags, isopropyl alcohol
Parts
brake fluid: mineral oil or DOT, as marked on the brake

When it needs doing

  • The lever feels soft or spongy, or its bite point moves during a long descent.
  • The lever pulls all the way to the bar.
  • A year has passed: fluid ages, and DOT fluid absorbs water.

The fluid comes first

Use only the fluid marked on the lever or caliper — mineral oil or DOT. The wrong one ruins the seals within days. DOT fluid also strips paint, so wear gloves and wipe up drips at once.

The outline

  1. Remove the wheel and the pads, and fit a bleed block between the pistons.
  2. Level the lever so its bleed port is the highest point.
  3. Push fresh fluid from the caliper up to the lever until no more bubbles come out.
  4. Close the ports, clean everything with alcohol, refit pads and wheel.
  5. Pump the lever until it is firm, then test the brake before riding.

Each brand's procedure differs in the details — follow the manual for your brake. If fluid reached the pads, replace them: contaminated pads do not recover.

Related articles

  • SRAM — An American component maker from Chicago, founded in 1987. It made the 1x mountain drivetrain mainstream and owns RockShox, Zipp and Quarq.
  • Shimano — A Japanese maker of bicycle components founded in 1921 in Sakai. Its drivetrains and brakes are on more bikes than any other brand's.
  • Disc brakes — Brakes that squeeze a steel rotor on the hub instead of the rim. Hydraulic disc brakes are the standard on mountain bikes: strong, controllable with one finger and unbothered by mud.
  • Braking — Braking well is braking in the right place: hard and early on good ground, then off the brakes where the trail is rough or turning. The front brake does most of the work.