BRAKE SYSTEMSGood brakes are a critical element for ensuring thesafe operation of equipment. The brake system appliesto all vehicles or equipment, such as pickup trucks,jeeps, tractor-trailers, and construction equipment.Braking systems must not only stop the unit but alsomust stop it in a smooth, uniform motion.Friction is the resistance in relative motion betweentwo surfaces in contact with each other. When astationary surface is forced into contact with a movingsurface, the rubbing action between the two surfacesslows down the moving surface. In nearly all brakesystems, the brake drums provide the moving surface,and the brake shoes provide the stationary surface. Thefriction between the brake drum and the brake shoesslows the drum and wheel; and the friction between thetire and the road surface slows and stops the vehicle.Part of your prestart and operator maintenanceresponsibilities consist of the following:lllllllUsing the proper brake fluidChecking the brake fluid levelInflating tires properlyChecking for loose connections or partsChecking for leaks in the systemDraining air reservoirs dailyChecking the self-contained lubricating oilsystem of air compressors dailyBrake troubles in vehicle operations that you mayencounter and must document are as follows:llllllllllThe brake pedal goes to the floorboard withno resistance.One brake drags.All brakes drag.The vehicle pulls to one side when braking.Soft or spongy pedal.Excessive pedal effort required.Noisy brakes.Air in the system.Loss of brake fluid.The brakes heat up during driving and failto release.Leaky brake cylinders.Grabbing braking action.The brake pedal can be depressed withoutslowing the vehicle.INDIVIDUAL BRAKESOn modern equipment, individual service brakesare provided for each wheel and are operated by a footpedal. The equipment also has an emergency or parkingbrake. The parking brake is operated by a separate pedalor a hand lever.Individual brakes are classified as the externalcontracting brake, the internal expanding brake, the discbrake, and the mechanical parking brake.External Contracting BrakesExternal contracting brakes are sometimes used forparking brakes on motor vehicles, for cranes, and forcontrolling the speed of auxiliary equipment driveshafts.In operation, the brake band (or shoe) of an externalcontracting brake is tightened around the rotating drumby moving the brake lever. The brake band is made ofcomparatively thin, flexible steel, shaped to fit the drum,with a frictional lining riveted to the inner surface (fig.3-38). his flexible band cannot withstand the highpressure required to produce the friction needed to stopa heavily loaded or fast-moving vehicle, but it workswell as a parking brake or hold brake.Figure 3-38.-External contracting brake.3-21
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