How the braking system works Modern cars have brakes on all four wheels, operated by a hydraulic system. The brakes may be disc type or drum type. The front brakes play a greater part in stopping the car than the rear ones, because braking throws the car weight forward on to the front wheels. Many cars therefore have disc brakes, which are generally more efficient, at the front and drum brakes at the rear. All-disc braking systems are used on some expensive or high-performance cars, and all-drum systems on some older or smaller cars. Brake hydraulics A hydraulic brake circuit has fluid-filled master and slave cylinders connected by pipes. When you push the brake pedal it depresses a piston in the master cylinder, forcing fluid along the pipe. The fluid travels to slave cylinders at each wheel and fills them, forcing pistons out to apply the brakes. Fluid pressure distributes itself evenly around the system. The combined surface 'pushing' area of all the slave pistons is much ... Read more »