Brake Master Cylinder

By David Sturtz, April 14, 2008

When the brake pedal is depressed, the brake master cylinder responds by generating the hydraulic pressure necessary to operate the braking system.

Symptoms of a Bad or Failing Brake Master Cylinder

  • A failing brake master cylinder can cause the brake pedal to sink, feel spongy, and be unresponsive when depressed. It may also feel like the brake pedal goes all the way to the floor when braking. This is a very serious condition—the car should not be driven.
  • A defective brake master cylinder can set a diagnostic trouble code and cause a warning light on the dashboard to illuminate

Brake Master Cylinder Related Repair Advice

  • The hydraulic brake system is sealed, so the fluid should not require frequent topping off. If it does, there is probably a leak.
  • Low brake fluid levels in the master cylinder reservoir could indicate worn brake pads. As brake pads wear, it is normal for brake fluid to be displaced to the brake calipers, causing the low levels.
  • The master cylinder may experience external or internal leaking. If your brake pedal sinks to the floor, it's most likely an internal leak.
  • The master cylinder has two hydraulic chambers for safety reasons. If a leak develops in one area of the brake system, the other chamber should remain functional for emergency purposes.
  • Problems elsewhere in the brake system can cause symptoms similar to a defective brake master cylinder, including stuck calipers and ABS valve bodies. Have the shop inspect the entire brake system to verify that the problem is specific to the master cylinder.
  • Flushing brake fluid every two years can extend the life of your brake master cylinders

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