Modern motorcycles use hydraulic brake and clutch systems to provide maximum stopping power or to compensate for the stiffer clutch springs used in high-powered engines. During normal usage, the brake fluid used by both systems will absorb condensation in the form of water. Brake fluid is thick by nature, allowing it to generate enough pressure to operate the brake calipers and clutch slave cylinder. But, the addition of water into the fluid creates a cushion-like effect that reduces hydraulic pressure. In order to remove the condensation, the brake fluid must be bled -- or drained -- out of the system and replaced with fresh fluid.
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Things you need
- Phillips screwdriver
- DOT 3 or 4 brake fluid
- Allen wrench set
- 8mm box-end wrench
- Three-feet, clear plastic tubing
- Plastic container
- Shop towels
Locate the master cylinder fluid reservoir. The front brake master cylinder is located on the right handlebar, while the clutch master cylinder is located on the left handlebar. The rear brake master cylinder is typically mounted near the right foot peg.
Remove the master cylinder fluid reservoir lid, either by hand or with a Phillips screwdriver. Pull the inner diaphragm out of the fluid reservoir, then suck the remaining fluid out with a siphon. Refill the fluid reservoir with fresh DOT 3 or 4 brake fluid.
Remove the side fairing panels from your motorcycle, using an Allen wrench, to provide access to the clutch slave cylinder on the left side of the engine. Skip this step if you are only working on the motorcycle's hydraulic brakes, or if your motorcycle is not equipped with fairings.
Pull the rubber dust cap off the bleed valve, located on the top or the sides of the brake caliper or clutch slave cylinder. Place an 8mm box-end wrench over the bleed valve.
Push a three-foot length of clear plastic tubing over the bleed valve nozzle, then place the opposite end of the tubing into a plastic container.
Turn the bleed valve counterclockwise a quarter-turn with the 8mm box-end wrench to open the valve. Pull the brake or clutch lever in completely, or push down on the rear brake pedal and hold it in place. Turn the bleed valve clockwise a quarter-turn to close the valve. Slowly release the lever or pedal to complete the bleed cycle.
Refill the master cylinder fluid reservoir with fresh DOT 3 or 4 brake fluid.
Look at the brake fluid that was forced into plastic tubing during the bleed cycle. Ideally, the fluid will have a light, amber colour and will be free of air bubbles or debris. Continue bleeding the hydraulic circuit, as described above, if the brake fluid appears dirty, dark in colour or contains air bubbles.
Tighten the bleed valve, using an 8mm box-end wrench, once the brake fluid in the plastic tubing resembles the fresh brake fluid contained in the master cylinder fluid reservoir. Pull the plastic tubing off the bleed valve, using a shop towel, then wipe away any spilt fluid. Push the rubber dust cap over the bleed valve nozzle.
Repeat the bleeding procedure for the second brake caliper, if your motorcycle is equipped with a dual-caliper front brake system.
Reinstall the side fairing panels onto your motorcycle, using an Allen wrench. Skip this step if you are only working on the motorcycle's hydraulic brakes or if your motorcycle is not equipped with fairings.
Refill the master cylinder fluid reservoir with fresh DOT 3 or 4 brake fluid until it is centred within the reservoir's sight level gauge. Push the inner diaphragm into the reservoir, then reinstall the fluid reservoir lid by hand or with a Phillips screwdriver.
Pump the clutch lever, brake lever or the rear brake pedal until you feel resistance, signifying that the hydraulic system has been pressurised.
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