how to bleed hydraulic mountain bike brakes

Over time, air bubbles may build up in your hydraulic disc brake lines, and that will lead to mushy braking. To overcome this, you should periodically (once every two years) bleed your brake lines. (It’s called bleeding because you are “bleeding” the air bubbles out of the system by adding some new fluid.)

Note: This will focus on Hayes disc brakes. Other brands or models of brakes may require slightly different procedures.

You will need:

  • Bleed kit for your brakes (DOT 4 brake fluid, small filler bottle, and small plastic hose)
  • Oil pan to catch used fluid
  • isopropyl alcohol for cleaning
  • a Phillips and flat screwdriver
  • 3-mm allen wrench
  • 8- and 10-mm box/open-end wrenches

Difficulty: 4/5

1. Remove wheel and brake pads.

The first thing to do is remove the wheel and remove the brake pads from the caliper. You don’t want to get brake fluid on the rotor or pads.

2. See Hayes Support.

Since bleeding is such an individual process (it varies for every single brake from every manufacturer,) I’ll just refer you to the Hayes website where you can download the exact instructions you need in a PDF format:

Hayes Support and FAQ Downloads


How to Bleed Shimano Disc Brakes


How To Bleed Avid Or SRAM Disc Brakes

What if you don’t have a bleed kit?

Ask a Mechanic: How to Bleed Your Brakes Without a Proper Bleed Kit

neat tips

The tools for this repair can be purchased at: Performance Bike, REI, or eBay.