How to Rebuild a 1980 Suzuki GS 550 Front Master Cylinder

Written by chris gilliland Google
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The first generation Suzuki's GS550 were built between 1977 and 1980, making the GS550 a classic machine by today's standards. Many on the surviving examples have fared well over time, but all too often require a refreshing of the front-brake master cylinder's internal parts. Problems associated with an old master cylinder range from fluid leaks, sticking brakes or a complete loss of braking ability. While many of the factory parts needed to rebuild the master cylinder are no longer available from Suzuki, purchase aftermarket rebuild kits containing all of the necessary parts from most Suzuki dealers.

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Things you need

  • Plastic drop clothes
  • Syringe
  • 8 and 14mm combination wrenches
  • Shop towels
  • Socket wrench
  • 10 and 14mm sockets
  • Plastic container
  • Phillips screwdriver
  • Pliers
  • Internal snap ring pliers
  • Thin wood dowel
  • Micrometer
  • DOT 3 brake fluid
  • Air compressor
  • Brake piston
  • Check valve
  • Spring
  • Primary cup
  • Reservoir O-ring
  • Rubber dust boot
  • Torque wrench
  • M10-by-1.25 Banjo bolt
  • Two crush washers
  • Two feet, 1/4-inch clear plastic tubing

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  1. 1

    Park the GS550 on a flat, level surface, using its centre stand. Cover the motorcycle's fuel tank with plastic drop clothes to avoid accidental brake fluid spills.

  2. 2

    Unscrew the front brake master cylinder reservoir cover by hand. Pull the rubber diaphragm out of the reservoir. Suck the brake fluid out of the reservoir, using a syringe.

  3. 3

    Loosen the brake-hose banjo bolt from the master cylinder, using a 14mm combination wrench. Wrap a shop towel around the bolt and the brake hose fitting, and then unscrew the bolt by hand. Remove the banjo bolt and both crush washers from the brake hose. Loosely tie the brake hose to the handlebars with a cable tie, keeping it as vertical as possible to prevent brake fluid from leaking from its fitting.

  4. 4

    Pull the cottar pin out of the base of the front brake lever pivot-bolt, using pliers. Unscrew the pivot bolt and nut from the master cylinder, using a socket wrench and a 10mm socket, and then remove the brake lever.

  5. 5

    Unscrew the front brake master cylinder bracket bolts, using a socket wrench and a 10mm socket. Pull the master cylinder away from the handlebar. Drain any brake fluid remaining in the master cylinder into a plastic container.

  6. 6

    Remove both screws from the plate on the bottom of the reservoir, using a Phillips screwdriver. Pull the reservoir off the master cylinder by hand. Remove the reservoir O-ring from the channel cut into the master cylinder body and discard it.

  7. 7

    Pull out the rubber dust boot covering the brake piston behind the brake lever pivot by hand. Remove the retaining snap ring from the master cylinder, using internal snap ring pliers. Pull the brake piston out of the master cylinder's bore. Insert a thin wooden dowel through the opposite end of the master cylinder and push the check valve, spring and primary cup out of the master cylinder's bore.

  8. 8

    Measure the master cylinder bore, using a micrometer. Inspect the master cylinder bore for deep scoring, scratches or pitting. Replace the master cylinder if it is damaged or if the bore is larger than 0.5547-inch.

  9. 9

    Clean the master cylinder in fresh DOT 3 brake fluid from a sealed container. Blow compressed air through the master cylinder bore and the reservoir fluid passages to clear out any obstructions.

  10. 10

    Soak the replacement brake piston, check valve, spring, primary cup and the reservoir O-ring in DOT 3 brake fluid.

  11. 11

    Coat the master cylinder bore with DOT 3 brake fluid, then insert the parts into the master cylinder in the following order: primary cup, spring, check valve and brake piston. Push the brake piston into the bore and install a new retaining snap ring, using internal snap ring pliers. Push a new rubber dust boot over the brake piston.

  12. 12

    Coat the bottom of the fluid reservoir, the reservoir O-ring and the channel cut into the master cylinder body with DOT 3 brake fluid. Push the O-ring into place, followed by the reservoir. Screw the reservoir screws into place with a Phillips screwdriver.

  13. 13

    Mount the master cylinder onto the right handlebar, placing it 2mm away from the right switch pod. Tighten the master cylinder bracket bolts to 6 foot-pounds, using a torque wrench and a 10mm socket.

  14. 14

    Mount the brake hose onto the master cylinder, using a new banjo bolt and crush washers. Tighten the banjo bolt to 13 foot-pounds, using a torque wrench and a 14mm socket.

  15. 15

    Fill the reservoir with DOT 3 brake fluid.

  16. 16

    Bleed the front brake system to remove trapped air from the master cylinder and brake hose. Place a two-foot length of 1/4-inch clear plastic tubing over the front-brake caliper bleed nozzle. Place the opposite end of the tubing into a plastic container. Turn the bleed nozzle a quarter-turn counterclockwise with an 8mm combination wrench, then pull in the front brake lever to push a small amount of brake fluid and air bubble into the tubing. Turn the bleed nozzle a quarter-turn clockwise and slowly release the brake lever. Refill the reservoir with brake fluid. Repeat until the tubing fills with bubble-free brake fluid.

  17. 17

    Refill the reservoir, and then reinsert the rubber diaphragm. Screw the reservoir cover on to the reservoir by hand.

Tips and warnings

  • Brake fluid is a solvent that will damage painted surfaces on contact. Wipe away spilt brake fluid and rinse with water immediately to reduce the risk of permanent damage.

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