When brakes are not as responsive as what they should be, or if the brake pedal “sinks” down to the floor, this is a possible indication of a braking system leak. It could be a brake fluid leak, or a brake hose air leak. One obvious sign that there is a brake fluid leak is a small puddle of fluid that is present underneath when the car is parked. Brake fluid is similar in appearance to motor oil, but with a texture that is less “slimy”.
The master cylinder is another possible problem. The cup seals or the cylinder bore may be worn. Any time that the brake pedal of a vehicle is fading towards the floor, internal leaking or cup seals being bypassed must be considered. A fading pedal that has no external leak is one of the most common master cylinder symptoms caused by the cup seals. It results in a loss of hydraulic pressure. It is likely that the vehicle will inch ahead at stop lights, as brake pedal fading occurs.