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DIY: Replace/Rebuild A Brake Master Cylinder

The brake master cylinder, indeed the whole brake system, is probably the most important part of your vehicle.
» Before You Start
» Brake Master Cylinder
» Removal
» Installation
» Master Cylinder Rebuild
» Bleeding The Brakes

Rebuilding The Master Cylinder

Rebuilding a brake master cylinder is not difficult and doesn't require any special tools. Nine times out of ten a master cylinder goes bad because it has an internally leaking seal or cup. Replacing these seals and cups will bring the master cylinder back to life.

Refer to figures 3 and 4 when performing the following procedures.


  1. Remove the master cylinder from the vehicle as follows:
  2. Disconnect and plug the hydraulic lines.
  3. Remove the two master cylinder-attaching nuts, then the master cylinder.
  4. Remove the reservoir cover and diaphragm. Discard the old brake fluid.
  5. Inspect the cover and diaphragm. Replace if it is cut, cracked or deformed.
  6. Remove the fluid level switch, if equipped.
  7. Depress the primary piston and remove the lock ring.
  8. Plug primary fluid outlet, outlet nearest to the cowl when master cylinder is installed, then apply compressed air into the secondary fluid outlet to remove the primary and secondary pistons.
  9. Remove the spring retainer and seals from the secondary piston.
  10. Clamp the master cylinder in a vise and remove the reservoir using a pry bar. Remove the reservoir grommets.
  11. Inspect the master cylinder bore for corrosion. Do not use abrasive material on master cylinder bore. Replace if the bore is corroded.
Brake Master Cylinder
Fig. 3. Internal Parts Of The Master Cylinder


  1. Clean all parts not included in the repair kit with brake fluid. Do not dry with compressed air. Lubricate all the rubber parts with clean brake fluid prior to installation.
  2. Lubricate the new reservoir grommets with silicone brake lube, then press the grommets into the master cylinder body. Ensure the grommets are properly seated.
  3. Lay the reservoir upside down on a flat, hard surface. Press the master cylinder body onto the reservoir using a rocking motion.
  4. Install new seals on the secondary piston, then the spring retainer.
  5. Install the spring and secondary piston assembly into the cylinder.
  6. Install the primary piston. Depress the primary piston into the cylinder and then install the lock ring.
  7. Install the fluid level switch, if equipped.
  8. Fit the diaphragm into the reservoir cover, and then install the cover onto the reservoir.
  9. Install the master cylinder and bleed the brake system.
Brake Master Cylinder
Fig. 4. Internal Parts Of The Master Cylinder


» Part 1       » Part 2       » Part 3       » Part 4
» Part 5       » Part 6

Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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