Brake/Clutch Bleeding 101
By Mark Shively
Bleeding the system:
Use high quality DOT 4 brake fluid (or preferred type) from a sealed container. Remove the old fluid from the master cylinder reservoir. Use a cooking type squeeze bulb baster to remove the bulk of the fluid from the reservoir. Use a clean paper towel to remove any remaining fluid. Top off the empty reservoir. Top it off periodically during this procedure. Avoid spillingbrake fluid on painted surfaces because it may damage the finish. The clutch/brake master cylinder reservoirsmay squirt brake fluid out the top if left uncapped during this procedure. Protect the area with towels, blankets, etc…
Fabricate a catch container easily from household items. Find a plastic container with a screw-on lid. Find a length of rubber hose with an inside diameter to fit the bleed valves. Put a hole in the lid just large enough to get the hose through. Connect one end of the hose on the clutch/brake caliper bleed valve. Put the drain container on the floor near the bleed valve. Insert the other end of the hose into the catch container’s lid to catch the runoff. Move the catch container to each bleed valve as you work, or fabricate more than one container.
Use a wrench to open the bleed valve while simultaneously squeezing the lever (or pedal). About 2/3 of a turn on the wrench will do. Fluid should pump through the hose at this time. Squeeze the lever to within 3/4 of a full lever pull and close the bleed valve. It’s important that you close the valve before hitting full travel on the lever. Release the lever and repeat the process (squeeze lever, open valve, close valve, release lever) until the lever is firm (pumps up).
If the lever fails to pump up, one or more of the following conditions may exist:
- -The brake fluid may contain air
- -Master cylinder contains air
- -Master cylinder gummed or defective
- -Caliper seals leaking, gummed, or defective
- -Banjo bolts & gaskets leaking or defective
- -Worn or defective hoses
The remedy may require bleeding the master cylinder before bleeding the system.
Methods of bleeding the master cylinder:
Method one: With master cylinder reservoir cap removed, monitor fluid and fluid transfer ports in reservoir while making slow, minute lever pulls. Fluid transfer ports are located in the base of the reservoir. Pulling the lever this way moves the master cylinder plunger equally slowly while just barely exposing fluid transfer ports. Such movement allows air in the master cylinder to escape that would not escape with normal lever pulls.
Method two: With master cylinder reservoir cap removed and fluid topped off, pull the lever a full-pull. With the lever against the handle bar, quickly release the lever. Let the lever slip away from your fingers. It should snap back. Monitor the reservoir fluid for evidence of bubbles or air in the system.
Continue these methods until the system builds pressure. Try alternating between the two methods. If the problem persists, install reservoir caps and let the motorcycle sit overnight or longer. Time allows air trapped in the system to travel to the highest point, usually the master cylinder. Bleed the system in the usual manner to complete the task. When bleeding multiple caliper systems, start at the point furthest away from the master cylinder and work towards the master cylinder.
If all fails, the master cylinder may be worn or defective and may need a rebuild kit or total replacement. Visit the following website to view microfiche parts: the site opens, select “OEM Parts” and then the “Year, Make, and Model” from the menus that follow. Purchase repair manuals from
Flushing the system:
Set up the catch container as if bleeding the system. Pump the lever a couple of times and open the bleed valve. With fluid flowing through the bleedvalve you can just keep pumping the lever until fresh, clean brake fluid runs through the system. Ensure the reservoir stays topped off. Once you’re satisfied the system is flushed, pull and hold the lever and close the bleed valve. If you bleed it dry, you'll have to start all over again. The end result is a flushed and bled system.