Brake master cylinders convert the pressure exerted from a driver's foot into hydraulic pressure, which moves other devices in the braking system to slow the car. Master cylinders can fail for many reasons, which can negatively affect braking performance.
Signs of master cylinder failure include a brake warning light. Wet spots appearing beneath the car and braking problems may also indicate master cylinder failure.
Mastercylinder failure symptoms include a brake pedal that slowly depresses when pressure is applied. Other signs include a lack of any braking action until the pedal is pressed against the floor.
Over time, the piston used to power the hydraulics in the braking system's master cylinder circuits can wear down, or the piston seal between the cylinder wall and piston can fail. Piston wear or seal failure can lead to brake cylinder failure. A brake line or hose leak can lead to wet spots beneath the car, along with a low fluid reservoir in the master cylinder and the activation of the brake warning light. A kinked brake line or debris in the brake fluid can prevent hydraulic pressure from releasing back to the master cylinder, which can cause brake pressure to drag.