The higher pressure of the outside air forces the diaphragm forward to push on the master-cylinder piston, and thereby assists the braking effort.
Pressing the brake pedal closes the valve linking the rear side of the diaphragm to the manifold, and opens a valve that lets in air from outside. When the brakes are off, both sides of the diaphragm are exposed to the vacuum from the manifold. The brake pedal pushes a rod that in turn pushes the master-cylinder piston.īut the brake pedal also works on a set of air valves, and there is a large rubber Such systems apply and release the brakes in rapid succession to stop them locking.Ī direct-acting servo is fitted between the brake pedal and the master cylinder. It closes when heavy braking raises hydraulic pressure to a level that might cause the rear brakes to lock, and prevents any further movement of fluid to them.Īdvanced cars may even have complex anti-lock systems that sense in various ways how the car is decelerating and whether any wheels are locking. Most cars now also have a load-sensitive pressure-limiting Under heavy braking, so much weight may come off the rear wheels that they lock, possibly causing a dangerous skid.įor this reason, the rear brakes are deliberately made less powerful than the front. Sometimes one circuit works the front brakes and one the rear brakes or each circuit works both front brakes and one of the rear brakes or one circuit works all four brakes and the other the front ones only. Most modern cars are fitted with twin hydraulic circuits, with two master cylinders in tandem, in case one should fail. To be exerted by the brakes, in the same way that a long-handledĬan easily lift a heavy object a short distance. The combined surface 'pushing' area of all the slave pistons is much greater than that of the piston in the master cylinder.Ĭonsequently, the master piston has to travel several inches to move the slave pistons the fraction of an inch it takes to apply the brakes. When you push the brake pedal it depresses aĪt each wheel and fills them, forcing pistons out to apply the brakes.ĭistributes itself evenly around the system.
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