How to Bleed Hydraulic Bicycle Brakes.




Introduction: How to Bleed Hydraulic Bicycle Brakes.


There are different hydraulic brake systems and they vary slightly in their bleeding procedure but the principle is broadly the same.

I am bleeding some Hope C2s on a friend's  gnarly bike.

They are old but beautifully engineered and are closed system hydraulic brakes.

There are kits to make things easier but this is the old school way using a simple hose.

Step 1: Tools and Consumables and Naming Parts.

You will need an 8mm spanner ( preferably ring ended).

A 26 mm spanner or an adjustable.

Some clean rags.

A small length of tubing or a bleed kit.

The correct brake fluid. ( Some use DOT some use mineral )

Step 2:

Remove the wheel and brake pads.

These pads are held in with two split pins; remove the pins and the pads just slide out.

Make sure that you do not touch the pad surface with your fingers as this will contaminate them.

Step 3: Taking the First Step.undo This . . . .

The bike needs to be held upright ; in a stand or held by someone or leant ; but make sure that it is stable.

The nipple on the brake caliper should be pointing upwards ( the rear one is already  but the front one will need temporarily undoing by one bolt to allow it to be swiveled upwards.)

Adjust the brake lever clamp so that it is horizontal to the ground.

Put paper on the ground underneath the lever and brake to catch excess fluid.

Undo the large polygon nut ( master cylinder cap ) on the brake lever with a 26mm spanner.

Step 4: Setting Up for Bleeding.

Put the 8mm spanner over the bleed nipple.

Attach the tubing to the nipple and attach a container or rag to catch the fluid.

Put rag around this to catch drips.

Step 5: Bleeding.

Top up the lever with the appropriate fluid.

Undo the nipple a quarter turn and slowly pull the brake lever in and hold it; tighten the nipple up.
Release the brake lever.

Undo the nipple a quarter turn and slowly pull the brake lever in and hold it; tighten the nipple up.
Release the brake lever.

Undo the nipple a quarter turn and slowly pull the brake lever in and hold it; tighten the nipple up.
Release the brake lever.

You get the idea . . .

You will see fluid coming up the hose; it will have bubbles in it.
Repeat this process until no more bubbles come out; but make sure that the fluid in the reservoir does not drop too low; keep topping it up.

Step 6: Replacing the Master Cylinder Cap.

This is a bit fiddly.

Unscrew the reservoir piston ( see 1st photo) from the master cylinder cap. (This a LEFT-HAND thread)

Top up the reservoir to the top and place rag around it.

Gently push the reservoir piston into the master cylinder so that the o-ring is just covered.

Clean up the drips.

Put the Master cylinder cap on the master cylinder and gently screw the silver adjuster anti-clockwise.

When this process has brought the whole assembly down low enough to engage the cap and the threads on the lever, then press gently down on the cap and screw the cap clock-wise by hand and then finish with a 26mm spanner.

Screw the adjuster anti-clockwise as far as it will comfortably go.

Inside the caliper you will see the pistons slightly poking out; undo the nipple once more to release fluid until they are flush with the inside of the caliper.

Clean up any fluid.

Step 7:

Replace the pads and wheel and screw the silver lever adjuster clock-wise until you achieve the sharpness of braking that you require.

Check for leaks and test ride.

Dispose of the old fluid  in a responsible way( as per instructions  on the bottle.)

Happy riding.

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    8 years ago

    magura use their own fluid called magura blood


    10 years ago on Introduction

    shimano uses mineral; oil,NOT DOT BRAKE FLUID! and hope, hayes,magura, avid all use a variation of DOT Fluid Do you homework you can do major damage if you use the wrong fluid!


    10 years ago on Introduction

    Generally, Shimano brakes use hydraulic oil, and hayes/avid use DOT brake fluid. If you are not sure a quick google solves most problems. Great instructable friendofhumanity!