Disc Brake Assembly

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Disc Brake Assembly Disc  brakes  are  basically  like  the  brakes  on  a ten-speed  bicycle.  The  friction  elements  are  shaped like pads and are squeezed inwards to clamp a rotating disc  or  wheel.  A  disc  brake  assembly  consists  of  a caliper, brake pads, rotor, and related hardware (bolts, clips, and springs), as shown in figure 7-16. BRAKE   CALIPER.—The caliper is the nonrotating unit in the system and it may be mounted to the  spindle  or  splash  shield  to  provide  support.  The brake  caliper  assembly  includes  the  caliper  housing, the  piston(s),  the  piston  seal(s),  the  dust  boot(s),  the brake pads or shoes, and the bleeder screw. The caliper is fitted with one or more pistons that are  hydraulically  actuated  by  the  fluid  pressure developed  in  the  system.  When  the  brake  pedal  is applied, brake fluid flows into the caliper cylinder. The piston is then forced outward by fluid pressure to apply the brake pads to the rotor. The  piston  seal  in  the  caliper  cylinder  prevents pressure leakage between the piston and cylinder. The piston  seal  also  helps  pull  the  piston  back  into  the cylinder  when  the  brakes  are  released.  The  elastic action of the seal acts as a spring to retract the piston and maintain a clearance of approximately 0.005 inch when the brakes are released. The piston boot keeps road dirt and water off the caliper  piston  and  wall  of  the  cylinder.  The  boot  and seal  fit  into  grooves  cut  in  the  caliper  cylinder  and p i s t o n . A bleeder screw allows air to be removed from the hydraulic system. It is threaded into the top or side of Figure 7-16.—Disc brake assembly. the caliper housing. When loosened, system pressure is used to force fluid and air out of the bleeder screw. DISC BRAKE PADS.—Disc  brake  pads  consist of steel shoes to which the lining is riveted or bonded. Brake pad linings are made of either asbestos (asbestos fiber  filled)  or  semimetallic  (metal  particle  filled) friction material. Many new vehicles, especially those with   front-wheel   drive,   use   semimetallic   linings. Semimetallic  linings  withstand  higher  operating temperatures without losing their frictional properties. Antirattle  clips  are  frequently  used  to  keep  the brake pads from vibrating and rattling. The clip snaps onto the brake pad to produce a force fit in the caliper. In some cases, an antirattle spring is used instead of a clip. A  pad  wear  indicator  (a  metal  tab)  informs  the operator of worn brake pad linings. The wear indicator produces an audible high-pitch squeak or squeal, as it scrapes  against  the  brake  disc.  This  harsh  noise  is  a result  of  the  linings  wearing  to  a  point,  allowing  the indicator  to  rub  against  the  brake  disc,  as  the  wheel turns. BRAKE  DISC.—Also    called    brake    rotor,    the brake disc uses friction from the brake pads to slow or stop the vehicle. Made of cast iron, the rotor may be an integral  part  of  the  wheel  hub.  However,  on  many front-wheel  drive  vehicles,  the  disc  and  hub  are separate units. The  brake  disc  may  be  a  ventilated  rib  or  solid type.  The  ventilated  rib  disc  is  hollow  that  allows cooling air to circulate inside the disc. Disc Brake Types Disc  brakes  can  be  classified  as  floating,  sliding, and  fixed  caliper  types.  Floating  and  sliding  are  the most  common  types.  The  fixed  caliper  may  be  found on older vehicles. FLOATING CALIPER.—The     floating     caliper type disc brake (fig. 7-17) is designed to move laterally on  its  mount.  This  movement  allows  the  caliper  to maintain a centered position with respect to the rotor. This design also permits the braking force to be applied equally to both sides of the rotor. The floating caliper usually  is  a  one-piece  solid  construction  and  uses  a single piston to develop the braking force. Operation of a floating caliper is as follows: Fluid  under  pressure  enters  the  piston  cavity  and forces the piston outward. As this happens the brake pad contacts the rotor. 7-15

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