How to Rebuild an MGB Slave Cylinder

Updated July 19, 2017

The slave cylinder on an MGB is the component of the sports car's hydraulic system that does the actual work of disengaging the clutch. The system incorporates a hydraulic master cylinder, a fluid reservoir, hydraulic lines and the slave cylinder, which is a small unit with an extendable rod at the end of a pressure-operated piston. Depressing the clutch pedal forces fluid from the clutch master cylinder to the slave cylinder. The fluid under pressure forces the slave cylinder piston forward. This causes a powerful extension of the rod, which in turn pushes the clutch throwout bearing release arm, which releases the clutch.

Raise the driver's side of the car with the floor jack. Place the jack stand under the frame for support and lower the car onto the jack stand. Remove the hydraulic line from the back of the slave cylinder with a wrench. Remove the two bolts that secure the cylinder to the side of the transmission with the appropriate socket.

Remove the rubber dust boot and extension rod by pulling it off. Unlock the snap ring that secures the cylinder piston in the front of the cylinder where the rod and boot were located with the snap ring pliers. Pull the piston and spring out of the cylinder.

Spray some brake cleaner into the cylinder bore to clean out the corrosion. Pour a small amount of brake fluid into the cylinder to coat the walls.

Install the honing tool in the drill and insert the cylinder hone in the slave cylinder bore. Spin the hone slowly and move it in and out several times, withdraw it and inspect the inner walls of the bore for remaining abrasions. Repeat the honing process until the bore is clean and smooth. Apply brake cleaner to the bore.

Clean the piston with brake cleaner and remove the rubber cups. Install the new cups (seals for the piston). Insert the piston into the cylinder bore and push in hard enough to allow room for the installation of the snap ring. A groove can be seen near the top of the cylinder bore into which the snap ring must rest. The piston must be below this groove so the snap ring will seat properly. Install the snap ring and push it down into the bore by hand until it snaps into place.

Install the rubber dust boot and rod. Place the rod in the pocket on the end of the throwout bearing release arm and swing the cylinder over to the transmission. Align the two holes, install the bolts and tighten with the socket. Install the hydraulic line and tighten with a wrench.

Open the slave cylinder bleeder valve on the side of the cylinder with a wrench. Refill the clutch master cylinder reservoir on the firewall with brake fluid. Close the bleeder screw with a wrench as soon as a steady drip of fluid is observed from the bleeder. Raise the car with the floor jack and remove the jack stand. Lower the car to the ground.

Things You'll Need

  • Floor jack
  • Jack stands
  • Set of sockets
  • Set of wrenches
  • Drill
  • Cylinder hone
  • Brake fluid
  • Clean rags
  • Can of brake cleaner
  • Slave cylinder rebuilding kit
  • Snap-ring pliers
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About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).