Figure 3-40.-Internal expanding brake.Figure 3-39.—External contracting transmission parkingbrake.Figure 3-39 shows an external contracting brake.The brake band is anchored opposite the point where thepressure is applied. In addition to supporting the band,the anchor allows adjustment of the brake liningclearance. Other adjusting screws and bolts are providedat the ends of the band.Internal Expanding BrakesInternal expanding brakes are used almostexclusively as wheel brakes, but can be found on somecranes. This type of brake permits a more compact andeconomical construction. The brake shoes andbrake-operating mechanism are supported on a backingplate or brake shield attached to the vehicle axle, asshown in figure 3-40. The brake drum, attached to therotating wheel, acts as a cover for the shoe and operatingmechanism and furnishes a frictional surface for thebrake shoes.The brake shoe of an internal expanding brake isforced outward against the drum to produce the brakingaction. One end of the shoe is hinged to the backing plateby an anchor pin, while the other end is unattached andcan be moved in its support by the operating mechanism.When force from the operating mechanism is applied tothe unattached end of the shoe, the shoe expands andbrakes the wheel. A retracting spring returns the shoe tothe original position when braking action is no longerrequired.Disc BrakesThe disc brake has a metal disc (rotor) and a pair offlat brake pads instead of a drum and curved brake3-22Figure 3-41.-Sectional view of a disc brake.shoes. Figure 3-41 shows a sectional view of a discbrake assembly. The two flat pads are on the two sidesof the disc. The assembly in which the flat pads are heldis the caliper assembly. In operation, the pads are forcedagainst the two sides of the disc by the movement of thepistons in the caliper assembly. The pistons are actuatedby hydraulic pressure from the master cylinder. Theeffect is to clamp the rotating disc between the stationarypads, as shown in figure 3-41.Mechanical Parking BrakeIn most vehicles, a hand lever or foot pedal engagesthe parking brake. The parking brake has its ownsystem and can be either an external contracting brakebands on the drive shaft (fig. 3-42, view A) or a
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business