BRAKE SYSTEMS Good brakes are a critical element for ensuring the safe operation of equipment. The brake system applies to all vehicles or equipment, such as pickup trucks, jeeps,  tractor-trailers,  and  construction  equipment. Braking systems must not only stop the unit but also must stop it in a smooth, uniform motion. Friction is the resistance in relative motion between two  surfaces  in  contact  with  each  other.  When  a stationary surface is forced into contact with a moving surface, the rubbing action between the two surfaces slows down the moving surface. In nearly all brake systems, the brake drums provide the moving surface, and the brake shoes provide the stationary surface. The friction  between  the  brake  drum  and  the  brake  shoes slows the drum and wheel; and the friction between the tire and the road surface slows and stops the vehicle. Part of your prestart and operator maintenance responsibilities  consist  of  the  following: l l l l l l l Using  the  proper  brake  fluid Checking the brake fluid level Inflating  tires  properly Checking  for  loose  connections  or  parts Checking for leaks in the system Draining  air  reservoirs  daily Checking   the   self-contained   lubricating   oil system of air compressors daily Brake troubles in vehicle operations that you may encounter and must document are as follows: l l l l l l l l l l The  brake  pedal  goes  to  the  floorboard  with no  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  fail to release. Leaky  brake  cylinders. Grabbing  braking  action. The  brake  pedal  can  be  depressed  without slowing the vehicle. INDIVIDUAL BRAKES On  modern  equipment,  individual  service  brakes are provided for each wheel and are operated by a foot pedal. The equipment also has an emergency or parking brake. The parking brake is operated by a separate pedal or a hand lever. Individual brakes are classified as the external contracting brake, the internal expanding brake, the disc brake, and the mechanical parking brake. External  Contracting  Brakes External contracting brakes are sometimes used for parking  brakes  on  motor  vehicles,  for  cranes,  and  for controlling  the  speed  of  auxiliary  equipment  drive shafts. In operation, the brake band (or shoe) of an external contracting brake is tightened around the rotating drum by moving the brake lever. The brake band is made of comparatively 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  high pressure required to produce the friction needed to stop a heavily loaded or fast-moving vehicle, but it works well as a parking brake or hold brake. Figure 3-38.-External contracting brake. 3-21