Your brake system's master cylinder controls the flow and pressure of the brake fluid through your brake lines. When you press the brake pedal, the master cylinder forces the air out of the reservoir and into the brake lines. From there it flows to the calipers to pressurize the piston and compress the brake pad against the rotor. If your master cylinder is failing, it can threaten the integrity of your entire braking system. Any time you're feeling changes in the way your brakes perform, you should consider examining your master cylinder. Here are a few brake symptoms that can indicate a failing master cylinder.
Deflated Brake Pedal
A deflated brake pedal is one that doesn't return to its standard position once you take your foot off it. If you push your brake pedal to the floor and it stays there, it could mean that the master cylinder isn't maintaining pressure in the system properly.
Fading Brake Pedal
If you press the brake pedal down and it sinks further to the floor even after you've stopped pressing, that's a sign that you might have a brake fluid leak. The leak prevents the system from sustaining its pressure. If your master cylinder is leaking, you'll need to have it replaced. To determine if the master cylinder is leaking, look around the seals where it mounts to the engine. If it's visibly damp, that's a good indication of a leak.
Lack of Fluid Flow
If you remove the top from your master cylinder, you should be able to see the brake fluid level fluctuate in the reservoir when you press the brakes. If the level isn't changing when you press the brakes, it means you may have a problem with the master cylinder seal.
Reduced Braking Ability
When your brake fluid isn't pressurized enough, you'll find that you have limited stopping power. This happens because the pressure between the cylinders isn't sufficient enough to press the pad to the rotor properly. If you're having to push the brake pedal further to get the same stopping power from your brakes, it's a sign that you're having pressurization problems in your braking system. This is often caused by problems with the master cylinder.
If you're seeing any of these symptoms, it is important to have your brakes examined by a mechanic right away. Your brake mechanic (such as one from Sterling Service Inc) can assess the condition of the master cylinder and ensure that everything is working as it is intended. If you need to have the master cylinder replaced, he or she can do that and bleed the brake system to restore its function.