mechanical linkage that works the rear wheel brakes(fig. 3-42, view B).HYDRAULIC BRAKE SYSTEMA hydraulic brake system is primarily a liquidconnection or coupling between the brake pedal and theindividual brake shoes and drums, as shown in figure3-43. The system consists of one master cylinderconnected by pipes and flexible tubing to the wheelcylinders. The wheel cylinders control the movement ofthe brake shoes at each wheel. When the brake pedal isdepressed, the hydraulic fluid forces the pistons in thewheel cylinder against the brake shoes, forcing the shoesagainst the brake drum or brake discs stopping thewheels.Hydraulic brakes are self-equalizing brakes. If theactuating pistons were all the same size, each brake inthe hydraulic system would receive an identicalhydraulic force when the brakes were applied, becausea force exerted at any point upon a closed liquid isdistributed equally through the liquid in all directions atthe same time. All brake systems have larger wheelcylinders in the front than in the rear. When you stop avehicle, more weight is automatically shifted forwarddue to inertia, so more front-wheel braking is required.The master cylinder is a reservoir for the brake fluidand contains pistons and valves which changemechanical force to hydraulic pressure when the brakepedal is depressed, as shown in figure 3-43. The pressureon the brake pedal moves the piston within the mastercylinder to force the brake fluid from the master cylinderthrough tubing and flexible hoses to the wheel cylinders.As pressure on the pedal is increased, greater hydraulicpressure is built up within the brake cylinders, and thusgreater force is exerted against the ends of the brakeshoes. When pressure on the pedal is released, theretracting springs on the brake shoes return the wheelcylinder pistons to their released positions. This actionforces the brake fluid back through the flexible hose andtubing to the master cylinder.Figure 3-42.-Parking brake configurations.3-23Figure 3-43.-Hydraulic brake system.
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