Hydraulic brakes can become spongy over time as air gets into the system and the oil breaks down. This is my guide to bleeding Shimano brakes taken from the mechanics on the Santa Cruz Syndicate team, for me this is the easiest way to service Shimano brakes.
For years I'd struggled with Avid / Sram brakes and bleeding them using DoT brake fluid and syringes, I always struggled to get them to bleed constantly. So when I built up my Bronson I made the switch to Shimano XT brakes, they use mineral oil, which a bit less nasty. They also can be bled using gravity instead of syringes and trying to pull vacuums.
How to Bleed Shimano Brakes
The Shimano bleed system is made up of a cup that fits to the lever master reservoir via the blee port and a tube that connects to the bleed port of the caliper. I don't use the tube on the caliper, instead I allow the fluid to flow out of the bleed hole over the caliper. This is to allow the fluid to clean lubricate the part of the piston that is exposed.
Check out the video guide for bleeding Shimano brakes.
Remove the caliper from the frame take out the brake pads, it's critical that no brake fluid comes into contact with either brake pads or the disc. Adjust the level on the bars so that the bleed port is the highest point of the system. Remove the bleed port cap and fit the bleed cup and fill with Shimano Brake fluid.
Holding the Caliper in a cloth, remove the bleed valve completely and let the fluid flow down from the lever. You'll see the dirty fluid and air come out. Allow the fluid to flow over the pistons, when the fluid comes out clean and free of bubbles replace the bleed valve.
Having cleaned the caliper of fluid refitted to the frame, either fit a brake block or the pads and wheel. Move on to the lever, with the reach and bit point set to maximum. It will help to note where you have them before doing this, so you can reset to your chosen position. With the bleed up still attached to the master reservoir, pump the level several times until air bubbles are no longer released.
You don't need many tools to complete a brake bleed, hex keys and 7mm spanner, along with the Shimano bleed kit is all that is required. Brake disc cleaner is handy to have to clean up afterwards, ensuring that there is no contamination is critical.
- Remove wheel
- Remove brake pads
- Remove caliper from frame
- Set reservoir to highest point
- Remove bleed screw from reservoir
- Fit bleed cup to Reservoir
- Fill cup with fluid
- Hold caliper in cloth and open bleed valve
- Allow fluid to run out until runs clear (don't allow cup to empty)
- Refit caliper bleed screw
- Wipe fluid from caliper
- Refit caliper to frame
- Pull level to bar and release several times until bubbles stop
- Remove cup and refit bleed screw
- Refit pads and wheel
Be careful not to allow the reservoir of fluid to empty, and clean up thoroughly afterwards to ensure you don't contaminate your pads or discs.