How to Bleed Hydraulic Disc Brakes: When You Need To and How It's Done

You need to bleed hydraulic brakes when the lever feels soft or pulls all the way to the bar, and as regular maintenance even if you don’t notice anything: SRAM says to do it at least once a year if the brake uses DOT fluid and every two years if it uses mineral oil. Bleeding means pushing the air out of the system and replacing the fluid. You can do it at home with your brand’s bleed kit, but one rule has no exceptions: every brake gets its own fluid, because mineral oil and DOT never mix.

Why brakes need bleeding

A hydraulic brake works because fluid doesn’t compress: whatever you push at the lever reaches the pistons in full. Air does compress, which is why a single bubble makes the lever sink and the brake lose its firm feel. Fluid also ages: it gets dirty, and DOT absorbs moisture from the air, which lowers its boiling point. SRAM describes the yearly bleed as the way to get rid of both air and moisture.

Signs it’s time to bleed:

• Spongy lever, or one that comes close to the bar when you squeeze hard.
• Inconsistent bite point: one day it grabs early, the next day late.
• Dark fluid in the reservoir or syringe.
• After cutting or replacing a hose, or swapping a lever or caliper.
• If the bike has traveled upside down or on its side for a long time and the lever has gone soft.

Before you bleed, rule out the easy stuff: worn pads, a contaminated rotor or a sticky piston. We cover them in our guide to disc brakes.

Mineral oil or DOT: never mix them

Each brake’s seals are made for one fluid. Put in the other and they swell or break down, and the brake can fail. The manufacturers’ warnings are clear:

• Shimano: only its original mineral oil, from a container that has been kept clean and sealed. Any other fluid can stop the brake from working.
• SRAM (mineral oil brakes): don’t use DOT 4 or DOT 5.1; only Maxima oil. On a DB8, DOT contamination degrades the seals and SRAM says to replace the brake.
• Park Tool: never put DOT in a mineral oil brake or vice versa, and never share a bleed kit between the two.

If you don’t know what your brake uses, check the lever, the reservoir cap or the manual. Don’t guess.

What you need

• Your brand’s bleed kit or a compatible one: syringe, tubing, threaded adapters and, for Shimano, the funnel (Shimano uses its TL-BR001 and TL-BR002 tools).
• The right fluid, fresh.
• Bleed block: a spacer that sits where the pads go so the pistons don’t pop out. Shimano’s is yellow.
• Hex and Torx keys, a 7 mm wrench, rags, gloves, safety glasses and isopropyl alcohol for cleanup.
• A container for the old fluid, which goes to your local household hazardous waste drop-off.

The basic steps

Every brand and lever model has its own procedure, with specific angles and positions. This is the general outline of a Shimano bleed according to Park Tool and Shimano’s manual; always follow the one for your brake.

1. Remove the wheel and the pads so they don’t get fluid on them. Push the pistons all the way back and fit the bleed block.
2. Position the bike so the hose runs uphill from the caliper to the lever with no loops: air always rises.
3. Level the lever so the bleed screw sits on top and horizontal.
4. Attach the funnel to the lever with a little oil in it.
5. Push oil up from the bottom: syringe on the caliper bleed nipple, open it a quarter to half turn and push until clean oil comes out into the funnel. Close it.
6. Work out the air: with the bleed nipple open, gently squeeze the lever and tap the hose and caliper to free bubbles. Never let the funnel run dry.
7. Pressurize: holding the lever squeezed, quickly open and close the bleed nipple; repeat until the lever is firm.
8. Purge air from the lever: tilt it into the positions your model calls for and squeeze it several times, watching for bubbles rising into the funnel.
9. Close up and clean: remove the funnel, refit the bleed screw with its O-ring and clean the lever and caliper with isopropyl alcohol.
10. Refit the pads and wheel, check that the lever is firm and the rotor doesn’t rub, and test the brakes a few times before you ride.

SRAM brakes use a different system (two syringes, one at the lever and one at the caliper), and on many models the caliper has a Bleeding Edge fitting that needs its own adapter.

When to take it to a bike shop

Bleeding isn’t hard, but a mistake leaves you without brakes. A mechanic should do it if:

• It’s your first time and nobody can show you.
• You’re not sure which fluid the brake uses.
• The job involves cutting hoses or routing the brake through the frame.
• The lever is still soft after bleeding: there may be a leak or a damaged seal. Shimano says never to ride a leaking brake.
• The wrong fluid went in: the brake needs new seals or replacing altogether.
• It’s an e-bike or cargo bike, which stops more weight and where a failure is more serious.

Park Tool calls it an advanced procedure and advises checking with the manufacturer if you have any doubts.

Common mistakes

• Mixing fluids or using the other system’s kit. The most expensive mistake.
• Leaving the pads in. One drop of fluid on them and they’re done.
• Letting the funnel or syringe run dry and drawing fresh air into the system.
• Squeezing the lever without the bleed block in the caliper: the pistons come out too far.
• Reusing fluid that came out. Always use fresh.
• Not cleaning up DOT that drips on the frame or rotor. Wipe it off paint immediately and clean the rotor with isopropyl alcohol.

Log the bleed date in My Bike or in your maintenance schedule by mileage. Brake vocabulary in six languages is in the brakes glossary.

Updated October 19, 2026 ·Report an error on this page