Although Honda’s line of motorcycles have a reputation for the use of high-quality components, parts such as the front brake master cylinder will need to be rebuilt eventually. Brake fluid leaks from the brake lever, fluid reservoir or brake fittings are the first signs of a compromised master cylinder and are often caused by wear or debris buildup. This can have a detrimental effect of the performance of the hand-operated brake, a dangerous situation that could lead to a crash. In most cases, the master cylinder can be rebuilt at a cost substantially less than replacing the entire assembly.
1) Unscrew the cover from the front brake master cylinder’s fluid reservoir and pull out the rubber diaphragm. Locate the drain valve on the brake caliper and attach a length of clear plastic tubing onto the valve’s nozzle. Place the opposite end of the tubing into a container. Open the valve with a wrench, turning the valve a quarter of a turn counterclockwise. Pump the brake lever repeatedly until the brake fluid has been drained completely from the front brake circuit and into your container.
2) Unplug the wiring from the front brake switch under the brake lever. Unscrew the oil bolt from the front brake master cylinder with a wrench. Pull the bolt, brake line and copper crush washers away from the master cylinder and allow any remaining brake fluid to drain into a container. Remove the master cylinder from the handlebar, using a socket wrench to unscrew the pair of bolts on the master cylinder’s perch.
3) Pull the dust cap off from the base of the fluid reservoir’s hose and remove the snap ring with a pair of snap ring pliers. Using a wrench, loosen the reservoir bracket’s bolt and remove the reservoir and hose from the master cylinder. Replace the O-ring on the base of the hose.
4) Unscrew the nut from the bottom of the brake lever’s pivot bolt with a wrench. Unscrew the pivot bolt from the master cylinder with flat screwdriver and remove the brake lever. Remove the brake switch from the master cylinder, using a Phillips screwdriver to unscrew its bolts.
5) Pull out the rubber dust from the master cylinder’s piston. Remove the piston’s snap ring with snap ring pliers and pull the piston and spring out of the master cylinder. Flush the master cylinder and reservoir out with clean DOT 4 brake fluid. Dry immediately with a clean shop towel.
6) Coat the new piston and spring with fresh brake fluid. Insert the piston and spring into the master cylinder. Install a new snap ring with a pair of snap ring pliers and place a new rubber dust boot over the end of the piston.
7) Insert the base of the fluid reservoir’s hose into the master cylinder. Use a pair of snap ring pliers to insert a new snap ring over the base of the hose. Slide a new dust cap over the base of the hose. Use a wrench to insert and tighten the reservoir bracket’s bolt.
8) Reinstall the brake lever, inserting the pivot bolt into the master cylinder and tightening it with a flat screwdriver. Use a socket wrench to screw the pivot bolt’s nut into place.
9) Reinstall the master cylinder onto the motorcycle in the reverse order of removal. Fill the master cylinder with fresh brake fluid. Bleed any trapped air out of the front brake circuit.
* Cover all painted and plastic surfaces with a towel or drop cloth to prevent spilled brake fluid from damaging their finish.
* Brake fluid is caustic and may cause skin and eye irritations. Wear gloves and eye protection at all times when working with your motorcycle’s brakes.
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