Quantcast Internal  Expanding  Brakes

Figure 3-40.-Internal expanding brake. Figure  3-39.—External  contracting  transmission  parking brake. Figure  3-39  shows  an  external  contracting  brake. The brake band is anchored opposite the point where the pressure  is  applied.  In  addition  to  supporting  the  band, the  anchor  allows  adjustment  of  the  brake  lining clearance. Other adjusting screws and bolts are provided at the ends of the band. Internal  Expanding  Brakes Internal  expanding  brakes  are  used  almost exclusively as wheel brakes, but can be found on some cranes. This type of brake permits a more compact and economical   construction.   The   brake   shoes   and brake-operating  mechanism  are  supported  on  a  backing plate or brake shield attached to the vehicle axle, as shown in figure 3-40. The brake drum, attached to the rotating wheel, acts as a cover for the shoe and operating mechanism and furnishes a frictional surface for the brake shoes. The brake shoe of an internal expanding brake is forced outward against the drum to produce the braking action. One end of the shoe is hinged to the backing plate by an anchor pin, while the other end is unattached and can be moved in its support by the operating mechanism. When force from the operating mechanism is applied to the unattached end of the shoe, the shoe expands and brakes the wheel. A retracting spring returns the shoe to the original position when braking action is no longer required. Disc Brakes The disc brake has a metal disc (rotor) and a pair of flat brake pads instead of a drum and curved brake 3-22 Figure 3-41.-Sectional view of a disc brake. shoes. Figure 3-41 shows a sectional view of a disc brake assembly. The two flat pads are on the two sides of the disc. The assembly in which the flat pads are held is the caliper assembly. In operation, the pads are forced against the two sides of the disc by the movement of the pistons in the caliper assembly. The pistons are actuated by hydraulic pressure from the master cylinder. The effect is to clamp the rotating disc between the stationary pads, as shown in figure 3-41. Mechanical  Parking  Brake In most vehicles, a hand lever or foot pedal engages the  parking  brake.  The  parking  brake  has  its  own system and can be either an external contracting brake bands  on  the  drive  shaft  (fig.  3-42,  view  A)  or  a


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