TRUCK SERVICE MANUAL TM 5-4210-230-14&P-1 DESCRIPTION The   hydraulic   system   used   to   actuate   the   brake mechanism consists of a compensating type master cylinder, in which the hydraulic pressure is originated; individual wheel cylinders,  in  which  the  hydraulic  pressure  is  applied,  which serve  to  actuate  the  brake  shoes  against  the  brake  drum  of each  wheel;  and  the  "line"  consisting  of  steel  tubing,  flexible hose,    brackets    and    unions,    interconnecting    the    master cylinder and wheel cylinders.  The master cylinder and wheel cylinders are fitted with pistons, all of which are provided with cup  packings,  which  act  as  a  seal  to  maintain  pressure  and prevent loss of brake fluid. Depressing  the  brake  pedal  moves  the  piston  within the  master  cylinder,  thus  displacing  the  brake  fluid  from  the master  cylinder  through  its  outlet  orifices,  tubing  and  flexible hose  connection  into  the  wheel  cylinders.    The  brake  fluid, being  non-compressible,  enters  each  of  the  wheel  cylinders, causing the cylinder pistons to move outward and actuate the brake shoes.  As pressure on the pedal is increased, greater hydraulic  pressure  is  built  up  within  the  wheel  cylinders  and, consequently, greater force is exerted against the shoes. When   the   pressure   on   the   pedal   is   released,   the brake  shoe  retracting  springs  return  the  brake  shoes  to  their normal  or  released  position.    The  return  movement  of  the brake shoes, in turn, causes movement of the wheel cylinder pistons  toward  their  released  position,  thus  forcing  the  fluid back through the tubing into the master cylinder. MAINTENANCE CHECKS The brake system should be checked periodically for evidence of needed repairs. It   is   difficult   to   determine   an   exact   maintenance interval  (time  or  mileage)  since  vehicles  will  be  used  in  wide varieties of operational applications and conditions. Brake adjustment should be checked every 3,000 km (2,000 miles).  Brake lining should be inspected every 19,000 km (12,000 miles) or every 12 months which ever occurs first. Before  starting  to  check  out  the  brake  system  itself, the  following  related  components  on  the  vehicle  should  be examined and serviced if found defective. 1. Tires. 2. Shock absorbers. 3. Wheel bearings. 4. Suspension. 5. Wheel alignment. The    following    procedure    is    given    as    an    aid    in checking out the brake system. BRAKE PEDAL 1. Pedal  return  should  be  unrestricted  when  pedal  is fully  released  (see  BRAKE  PEDAL  ADJUSTMENTS in Chapter III). 2. Excessive   side   movement   indicates   worn   pedal mounting. 3. Interference should not occur when pedal is depressed. 4. There should be ample clearance between pedal and toe   board   when   pedal   is   fully   depressed   (brakes applied). 5. Pedal    height    should    be    corrected    (see    BRAKE PEDAL ADJUSTMENTS in Chapter III). POWER CYLINDER To  check  power  cylinder  for  correct  operation,  refer to   the   respective   "Power   Cylinder"   section   of   this   Service Manual. MASTER CYLINDER 1. Fluid  level  should  be  6.4  to  12.7  mm  (1/4  to  1/2") from top of reservoir. 2. Master cylinder vent must be clear and unrestricted. 3. Check for external leaks at hydraulic line connections or at push rod end. CTS-2055S  Chapter 1  Page 3 PRINTED IN UNITED STATES OF AMERICA