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TRUCK SERVICE MANUAL TM 5-4210-230-14&P-1 DESCRIPTION These   self-adjusting   type   brakes   have   two   single   end wheel    cylinders,    each    operating    a    forward    acting    shoe providing directional braking response.  The closed end of the wheel  cylinder  has  a  slotted  ramp  which  is  the  self-centering sliding anchor for the opposite shoe.  The two wheel cylinder pistons  apply  equal  amounts  of  hydraulic  force  to  each  shoe toe. Shoes are adjustable manually by means of two hex head friction   spring   locked   studs,   exposed   on   the   backing   plate (Fig.  1).  Each stud rotates an adjuster cam located under a brake   shoe   table.      Shoe   hold-downs   consist   of   two   plain washers, multi-rattle wave washer between and a C-clip fitted over  the  extended  shank  of  the  cam  stud.    Two  retracting springs are hooked between the shoes and have their longer shanks connected to the anchor end of the shoes. The   function   of   the   contact   plug   type   self   adjusting mechanism  is  to  maintain  a  nearly  constant  previously  set running  clearance  between  brake  shoe  and  drum  throughout the life of the brake lining. The self adjusting mechanism is contained entirely in the brake   shoe.      This   mechanism   incorporates   a   contact   plug located   in   the   center   of   the   lining   and   is   the   lining   wear sensing component.  This plug is pinned (lever actuating pin) in a free rotatable manner to the adjusting lever, which in turn makes   contact   with   the   manually   operated   adjusting   cam. This  lever  in  turn  is  pinned  (lever  pivot  pin)  in  a  rotatable manner   through   a   hole   in   the   shoe   web.      As   lining   wear progresses,   the   contact   plug   is   gradually   depressed   upon successive  brake  applications  and  a  spring-actuated  wedge with  serrated  teeth  on  the  angular  surface  advance  between the lever-actuating pin and a stationary but rotatable serrated wedge pin, thereby maintaining the adjustment. Force is exerted by the lever actuating spring on the lever actuating  pin  acting  through  the  wedge  and  wedge  guide  pin so as to maintain firm contact between these parts while the brake is in the released position. Shoe  adjustment  is  accomplished  by  the  adjusting  lever changing position with relation to the shoe web as the contact plug  is  depressed.    The  adjusting  lever  then  comes  to  rest against the adjusting cam, causing the shoe to remain in the advanced or adjusted position. BRAKE SHOE REMOVAL 1 Position  vehicle  on  floor  stands  so  that  the  wheels are free to turn. 2. Remove wheel hub and drum assemblies. 3. Secure    pistons    in    wheel    cylinders    with    cylinder clamps. 4. Remove brake shoe retracting springs. 5. Remove   brake   shoe   guide   "C"  washer,   two   shoe guide  washers  and  wave  washer  from  each  shoe. Refer to Fig.  3 (items 16, 17 and 18). 6. Pull  shoes  free  from  adjuster  cams  and  then  rotate shoe    from    brake    group    freeing    ends    of    wheel cylinders. 7. After  shoes  are  removed  disassemble  self  adjuster mechanism on each shoe: a. Disconnect wedge (coil) spring from finger on wedge and remove spring. b. Unhook    torsion    adjuster    spring    from    shoe web. c. Work  torsion  adjuster  spring  coil  from  lever pivot pin and slide U-hook off plug-lever pin. d. Pull adjuster lever from opposite side of shoe and   contact   plug   out   of   shoe   table,   freeing wedge   retaining   washer,   wedge   and   wedge guide. CLEANING AND INSPECTION Thoroughly clean all parts (except drums) free of dirt and grease with cleaning solvent and wipe dry. Because     studies     have     indicated     that     exposure     to excessive amounts of asbestos dust may be a potential health hazard,  OSHA  has  set  maximum  limits  of  levels  of  airborne asbestos dust to which workers may be exposed.  Since most automotive    friction    materials    normally    contain    a    sizable amount  of  asbestos,  it  is  important  that  people  who  handle brake    linings    be    aware    of    the    problem    and    know    the precautions to be taken. OSHA   standards   should   be   consulted   with   respect   to mandatory requirements as well as for suggested procedures to minimize exposure. DRUMS, SHOES AND LINING For  complete  details  pertaining  to  reconditioning  drums and shoes, refer to CTS-2779. (Cont'd.  on next page) CTS-2491T  Page 3 PRINTED IN UNITED STATES OF AMERIC A

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