* Reduced braking power: The brakes feel spongy, require more pedal travel, or brake less effectively than normal. This is often an early warning sign of a failing master cylinder.
* Complete brake failure: In a more severe failure, you'll have no brakes at all. The brake pedal will go straight to the floor with no resistance.
The consequences of master cylinder failure are extremely dangerous. Without brakes, you risk a serious accident. If you suspect your master cylinder is failing, do not drive the vehicle. Have it towed to a qualified mechanic for repair or replacement.