It is the pressure generated by the Mazda brake master cylinder that makes it possible for the brake system on your vehicle to operate properly. This braking component is located on the opposite side of the fire wall from the brake pedal. There are two chambers in the brake master cylinder your Mazda uses. The rear chamber is allocated for use by the front braking system while the front chamber is for the rear brakes. This braking component has a piston in the bottom of it that is connected to both chambers and is what creates the pressure so the hydraulic system can be utilized. It is the seals on the piston in the brake master cylinder that will fail over time. This is a polymer component that will split or crack and be in need of replacing. On a Mazda, the leaking of the piston in a brake master cylinder will only have one symptom. This is the inability of pressure to be built up in the brake lines because of the fluid leaking past the blown seal. There is no outward leak that can be observed. If the brake pedal is soft and will not be able to stabilize the pressure as it continues to move towards the floor, then this brake master cylinder should be suspected of failing. While this symptom is similar to a leaking brake line or hose, a failed master cylinder will not leave a puddle of brake fluid under your wheels... a leaking hose will. The replacement of the Mazda brake master cylinder is a simple easy procedure. Once the brake lines are disconnected, the two hold down nuts are removed and the new one put into place. With everything reconnected, the brake lines on your Mazda then have to be bled of air before it is ready for the road.