1985 RZ350

RZ350 - Front Master Cylinder

The master cylinder is mounted to the right hand side of the handle bars. It is basically a small reservoir for hydraulic fluid, and a small piston pump to move the fuid mdown the hydraulic line and activate the caliper. It is rare that you'd need to overhaul the assembly, but mine had been sitting for years and I figured I'd rather be safe than sorry.

To remove the master cyclinder from the bike, you will need to disconnect the brake switch electrical connection inside the headlight, and remove the hydraulic line from the master cylinder body. In the shot above my hydraulic line was still connected to the master. The master cylinder comes off the bars by removing the two small bolts on the handlebar clamp.

To remove the lever, use two wrenches on either side of the pivot bolt and loosen them.

Then the pivot bolt can be removed and the lever will be free to pull from the cast aluminum bracket casting.

Be sure not to loose the small spring once the lever is removed.

I plan on refinishing the master cylinder housing so I also removed the brake switch. It can be removed by flipping the master cylinder over, and pushing in a small clip from the underside. Then it can be pulled clear.

Before the master cylinder piston is replaced, all the hydraulic fluid should be drained from the reservoir. Remove the two small screws that hold the top in place.

Remove the top and pour out the extra hydraulic fluid.

The master cylinder piston is located beyond the lever mount. Remove the small rubber dust cap and you'll see the end of the piston and the circlip that retains it. I found that getting the circlip out with circlip pliers was almost impossible becuase the end holes were partially hidden in the groove. I knew I had a second (new) circlip in the rebuild kit so I managed to hook one end of the existing one and just pulled...

..and it finally came out but was not able to be reused. At this point the internal spring in the piston will push the pison parts out of the casting.

Remove them from the casting but keep good notes on the order in which they need to be reassembled. First is the spring, then a rubber cap, then the metal piston casting with a rubber seal around it.

The rebuild kit from Yamaha contains all new rubber parts, a new metal piston casting, a spring, and a new circlip.

The new seal needs to be installed over the metal piston casting in the direction shown. I found the easiest way to do this was to slide it over the small end (to the right above) and then stretch it over the first ridge.

Build the parts up in the same way that the old ones were removed. Use a little clean hydraulic fluid to lubricate the seals.

Insert the entire assembly into the master cylinder housing. I sanded down the casting with steel wool and refinished the metal with special casing paint. If you do the same, be sure to tape off all holes and openings to keep paint out of the working areas.

Push the piston assembly in and refit the new circlip. This is easy to do with circlip pliers because you can get access to the clip ends but these become partially hidden when installed. Finally fit the new dust seal and refit the single small lever spring.

Refit the lever with some grease around the pivot point and the point where the lever makes contact with the end of the master cylinder piston. Tighten the pinch bolt and refit the brake switch if it was removed during the rebuild.

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