TM 5-3825-226-24 AIR CHAMBER AND MASTER CYLINDER 1.  Stroke indicator. 2.  Master cylinder. 1. Start  the  diesel  engine  and  let  the  air  pressure in the reservoir go up to cutout pressure. 2. Push  the  brake  pedal  down  and  keep  it  in  that position. 3. Look at the stroke indicator. a. Slow   movement   of   the   stroke   indicator after it has stopped once, is an indication that   there   is   leakage   in   the   hydraulic section  of  the  brake  system  or  that  the cup is cut. b. Extra  travel  of  the  stroke  indicator  (with brake  linings  in  contact  with  discs)  is  an indication    that    air    is    in    the    hydraulic section of the system. 4. Release the brake pedal. a. If    either    one    or    both    of    the    stroke indicators    do    not    retract,    this    is    an indication that a bypass opening in one of the   master   cylinders   is   closed   by   dirt, corrosion or the primary cup has become too large. NOTE:  A primary cup which has become too large is an indication of wrong or dirty hydraulic fluid in the system. If    hydraulic    fluid    is    dirty,    remove    and    repair    all components   in   the   hydraulic   system   of   the   brakes. Flush the brake lines with clean hydraulic fluid. Check for Leakage 1. Push   brake   pedal   down   and   keep   it   in   that position. 2. Put soap suds on the connections of the air lines at    the    master    cylinders    and    check    for    air leakage. 3. Release the pedal. 4. Put  soap  suds  on  the  exhaust  openings  of  the control valve for the brakes. 5. When  the  pedal  is  pushed  down,  leakage  must not  be  more  than  a  1.00  in.    (25.4  mm)  soap bubble in one minute. 6. Repair any air leaks that are found. HYDRAULIC BRAKE SYSTEM SERVICING Use  heavy  duty  hydraulic  brake  fluids  meeting  SAE J1703C   specifications   only.      Other   fluids   may   cause damage to rubber parts. Do not let dirt or other material get in the brake fluid when the hydraulic brake system is serviced.  Most parts cleaners  may  be  used  to  clean  master  cylinders  and wheel cylinders if the parts are then thoroughly washed with denatured alcohol or brake fluid to remove all of the solvent.    After  removal  of  the  solvent,  dry  parts  and protect from dust until cylinders are reassembled.  Wash the  rubber  parts  in  clean  denatured  alcohol  or  brake fluid. CAUTION:    Do  not  use  mineral  base  cleaning  solvent such as gasoline, kerosene, distillate, carbon tetrachloride,    acetone,    paint    thinner,    etc.        These solvents  will  damage  rubber  parts  and  cause  them  to become soft and of no use. AIR REMOVAL FROM BRAKES (Bleeding the Brakes) VALVES THAT LET THE AIR OUT (Bleed Screws) 5-18