Signs that it may be time for a new master brake cylinder include the activation of the brake light on the dashboard, a brake fluid leak or a soft brake pedal. Brake fluid is clear and shows up either beneath the car or inside the car beneath the brake pedal.
The brake master cylinder holds brake fluid and links to the whole brake system through hoses and pipes. When the driver steps on the brake pedal, fluid runs from the master cylinder to the braking unit near each wheel, causing friction to bring the car to a stop. Seals both inside and outside the cylinder wear out over the lifetime of the car.
When the external seals wear out, brake fluid leaks, draining the system and leading to eventual malfunction. Fluid sometimes leaks into the brake booster, ruining it. The booster is necessary for proper brake function, so if it is ruined, a replacement is necessary. When the internal seals wear out, the brake fluid stays in the cylinder instead of going to the brakes. This makes the brake performance less effective. The pedal feels soft and goes to the floor when the driver pushes it without stopping the car.