Signs of a bad master cylinder are having to push down the brake pedal much farther and harder than usual to slow down and stop. The master brake cylinder's job is to help provide stopping power.
The master cylinder equalizes pressure through the brake lines as the brake pedal is depressed, and distributes that pressure among the front and rear tires. Liquid in two chambers of the cylinder is pressurized and balanced according to how quickly and how hard the brakes are applied.
A bad master brake cylinder is usually leaking some of the fluid in one of the two chambers. This means that, although the rest of the braking system will work to move fluid through the brake lines, when it reaches the master cylinder, some of the fluid will leak out, causing the brakes to feel soft. If the failure is in one of the lines or in the linkage between the chambers of the master cylinder, the problem can be easy to fix. If damage has been caused to the cylinder itself, it may need replacing, which can result in expensive repair work. Any problem with a car's brake system should be addressed immediately, especially when a car's braking power has been reduced due to a failure in the master brake cylinder.