How to Replace a Brake Master Cylinder

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Here's how to replace or rebuild your brake master cylinder on a Toyota or Lexus vehicle.

Some times older vehicles may have a brake master cylinder that has worn out and needs to be replaced or rebuilt. The symptoms of a bad master cylinder include a soft, mushy or unresponsive brake pedal or leaking brake fluid.

The master cylinder consists of two pistons in series within one cylinder. They work together to depress the brake fluid, with each piston sending fluid to two diagonally opposing wheels as a safety precaution.

Sometimes the rubber seals wear out and fluid is no longer compressed properly, compromising braking. Furthermore, fluid might be leaking past the rear piston and into the brake booster, absorbing moisture, causing rust.

The correct this, the seals should be replaced and the braking system should be properly bleed of air.

After removing the strut bar and air intake box, the master cylinder can be removed by two 12mm nuts holding it to the brake booster, as well as the two brake lines. Suck as much fluid out of the reservoir before disconnecting the lines to minimize spillage.

With the master cylinder removed, you can opt to rebuild it. The reservoir is held in by a phillips screw, and its low brake fluid sensor can simply be popped out with a screw driver. Its a reed switch with a magnetic float.

Changing the piston seals is as easy as compressing the piston with a screw driver, and with the reservoir removed, turned upsided down for the holding pins to fall out. The two pistons and springs can then be removed and swapped for new ones.

If the piston is really worn out inside, it should be re-bored or replaced.

Bench bleeding is recommended before reconnecting the master cylinder to the brake lines. That way, the air in the cylinder won't have to be bled through the entire system. To bench bleed, connect two brake fittings and their hoses to the two ports on the master cylinder. Fill the reservoir and route the two lines back into the reservoir. Cycle the piston with a screw driver a few times, this will drive out the air and the fluid will go back into the reservoir.

The video demonstrates a more crude way to bench bleed the master cylinder without using a kit, as the repair manual states. Simply use your fingers to block the ports when releasing the brake pedal, so it sucks fluid back into the piston instead of air, then reconnect the lines.

Care must be taken when spilling brake fluid on painted surfaces, as it will damage it and it should be cleaned immediately. Keep the containers closed as brake fluid is hydroscopic and will absorb moisture causing rusty brake lines and components. Use DOT 3 brake fluid in Toyota vehicles.

Finally bleed the brakes as per this video:


If the pedal is still too mushy, drive the car on a dirt or snowy road, slam on the brakes to engage the ABS. This will cycle the pump (and any air within the ABS system), which can then be rebled a second time to rid the system of air.

Hybrid vehicles require the use of Toyota Techstream to cycle the ABS pump for bleeding.

The procedure is the same across most Toyota, Scion and Lexus non-hybrid vehicles, such as the Camry, Corolla, Sienna, Highlander, Solara, Yaris as well as the Lexus ES300, ES330, ES350, RX300, RX330 and RX350.

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