If your hydraulic bike brakes are feeling soft, mushy, or non-responsive, it’s time for a bleed. Trapped air inside your brake lines is the number one enemy of stopping power, compromising both your performance and safety on the road or trail.
This DIY tutorial breaks down the complete Hydraulic Disc Brake Bleeding Procedure into simple, easy-to-follow steps. Whether you're a seasoned mechanic or a first-time DIYer, this guide will help you eliminate air pockets, refresh your system, and successfully restore maximum stopping power to your ride. Let’s dive in!
Hydraulic Disc Brake Bleeding Procedure
Preparation
-
Identify Brake Fluid Type
- Shimano, Magura, and Tektro brakes use mineral oil.
- SRAM, Avid, and Formula brakes use DOT fluid (corrosive, handle with care).
- Never mix fluid types, as this will damage seals and ruin your brake system.
-
Clean & Protect
- Wipe the brake lever reservoir and caliper bleed bolt areas with a clean cloth to prevent dirt from entering the system.
- Wear gloves and have plenty of rags ready (fluid can damage paint and skin).
-
Secure the Bike
- Place the bike on a repair stand or flip it upside down, ensuring the brake lever is higher than the caliper. This helps air rise out of the fluid lines.
Step 1: Remove Old Fluid
- Use a hex key to loosen the bleed bolt on the caliper, then attach the clear syringe (for fluid removal) to the caliper bleed port.
- Unscrew the reservoir cap on the brake lever. Slowly pull the syringe plunger to draw old fluid and air out of the line.
- Once no more bubbles appear and the fluid runs clear, tighten the caliper bleed bolt first, then remove the syringe.
Step 2: Inject New Fluid
- Fill the red syringe with fresh brake fluid, hold it upright, and gently push the plunger to expel any trapped air from the syringe.
- Use a bleed adapter to connect the syringe to the brake lever reservoir, ensuring a tight, airtight seal.
- Slowly push the plunger to force new fluid through the line. Watch the caliper bleed port until clean, bubble-free fluid flows out steadily.
- As soon as consistent fluid flow is achieved, tighten the caliper bleed bolt immediately while maintaining pressure on the plunger to prevent air from being sucked back in.
Step 3: Purge Air from the System
- Keep the syringe connected to the lever reservoir. Tap the brake hose, lever, and caliper body gently to encourage any remaining small bubbles to rise into the syringe.
- Pull the plunger slowly to draw bubbles into the syringe. Repeat 2–3 times until no more bubbles are visible in the fluid.
- Tighten the reservoir cap on the brake lever, then disconnect the syringe.
Step 4: Final Checks & Testing
- Wipe up any spilled fluid around the reservoir and bleed bolt with a clean rag.
- Squeeze the brake lever repeatedly to check for a firm, consistent feel. If the lever feels spongy, repeat the air-purging steps.
- Spin the wheel and test brake performance to ensure strong stopping power, and check all connections for leaks.
- Once everything is confirmed to be working properly, the bike is ready to ride.
