TM 5-3825-226-24 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, distillant, 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 (WATER DISTRIBUTOR BRAKES) (Bleed Screws) Let the air out of system for the wheel brakes which is activated by the master cylinder. 1. Check   the   fluid   level   in   the   reservoir.      The primary level must be .5 in.  (12.7 mm) from the top of the reservoir. NOTE To    keep    air    out    of    the    master cylinder,  fluid  must  always  be  seen in the reservoir while air is being let out  of  the  system.    When  filling  an empty   system,   loosen   the   caps   on the master cylinders until fluid comes out, then tighten the caps. 2-141 VALVES THAT LET THE AIR OUT (TRACTOR BRAKES) (Bleed Screws)