TM 10-3930-653-14&P The   braking   operation   in   forward   travel   is   as   follows: (See  Fig.4-445)  The  primary  and  secondary  shoes  are forced   by   an   equal   force   by   operation   of   the   wheel cylinder  to  bring  the  lining  in  contact    with    the  brake drum.  The primary shoe forces the adjuster with the aid of  lining-to-drum  friction  force.  Due  to  this,  the  adjuster pushes  the  adjuster  end  of  the  secondary  shoe  by   a larger   force   than   that   offered   by   the   wheel   cylinder operation.    The  secondary  shoe  anchor  end  is  forced strongly  against  the  anchor  pin,  providing  large  braking force.      On   the   other   hand,   the   braking   operation   in reverse  travel  is  performed  in  the  reverse  direction,  but the   braking   force   is   the   same   as   in   the   case   of   the forward travel. Fig.  4-445.  Braking Operation in Fwd Travel Fig.  4-446.  Braking Operation in Rev. Travel AUTOMATIC CLEARANCE ADJUSTER The  automatic  clearance  adjuster  keeps  a  lining-to-brake  drum  clearance  of  0.38-0.58  mm  (0.015-0.023  in) automatically.  This adjuster, however, actuates only when the truck is braked in reverse travel.  When the brake pedal is pressed in reverse travel, the brake shoes are expanded.  As a result of this, the secondary and primary shoes come into contact with the brake drum and rotate together until the upper end of the primary shoe comes into contact with the anchor pin.  On  the  other  hand,  as  the  secondary  shoe  leaves  the  anchor  pin,  the  section  (A)  of  the  adjuster  lever  is  relatively pulled.    Therefore,  the  adjuster  lever  turns  around  the  section  (B)  so  that  the  section  (C)  of  the  adjuster  lever  shifts upwards, causing the section (D) of the adjuster to turn to the right.  As the brake pedal is further pressed, compression force   applied   on   the   adjuster   thread   becomes   larger.      This   causes   the   overtravel   spring   to   actuate   to   prevent overadjustment of the clearance, thus offering a smooth, fixed pedal feeling to the operator. 4-225