FIRST SPEED FORWARD When  the  console  selector  lever  is  moved  from  the NEUTRAL   position   to   the   FIRST   SPEED   FORWARD position, spool (14) for direction selection is moved to the FORWARD    position.        With    spool    (14)    for    direction selection  in  the  FORWARD  position,  the  passages  for No.  1 and No.  2 clutches are open to the reservoir.  The pressure oil for these clutches goes to the reservoir and neither is engaged. Also,   with   spool   (14)   for   direction   selection   in   the FORWARD position, the passages for the No.    6  clutch is  open  to  the  flow  of  oil.    As  the  No.    6  clutch  fills,  the pressure of the oil in the system has a decrease. When  the  oil  pressure  has  a  decrease,  the  spring force on modulation relief valve (2) moves the modulation relief valve to the left against its slug.  When the modulation relief valve moves to the left, it stops the flow of oil from the passages for oil going to torque converter (4). An orifice in the passage to the left end of differential and safety valve (6) controls  the  flow  of  oil  from  the  left end  of  the  combination  valve.    This  orifice  keeps  the combination  valve  from  being  moved  completely  to  the left  by  the  spring  force  during  a  normal  shift  sequence. This keeps the differential and safety valve from working as a safety valve between shifts. When the No.  6 clutch is filled, the oil pump causes an increase in the pressure of the oil.  Pressure oil goes through a passage and a drilled hole in modulation relief valve  (2)  to  the  left  end  of  differential  and  safety  valve (6).    The  pressure  oil  in  the  drilled  hole  in  modulation relief  valve  (2)  also  opens  its  poppet  valve  and  works between the slug and the modulation relief valve. As  PI  pressure  oil  has  an  increase,  differential  and safety  valve  (6)  is  moved  to  the  right.    The  passage  to the     reservoir     that     stopped     the     movement     of     the differential  and  safety  valve  in  NEUTRAL  now  has  PI pressure   oil.      This   valve   moves   to   the   right   until   the orifices in the valve are open to the P I1 pressure oil from selector valve (19).  The orifices control the flow of oil to the No.  3 clutch.  When the No.  3 clutch is filled, the P2 pressure  oil  plus  the  spring  force  move  differential  and safety valve (6) to the left to stop the flow of oil through the orifices.  Now PI pressure has an increase. As   the   P1   pressure   oil   has   an   increase,   the   PI pressure  between  the  slug  and  modulation  relief  valve (2) moves the modulation relief valve to the right.  When the modulation relief valve moves to the right, it connects the  passages  to  let  pressure  oil  go  to  torque  converter (4).  PI pressure also goes through the orifice to the right of  load  piston  (3).    The  P1  pressure  on  the  load  piston, plus  the  spring  force,  makes  modulation  relief  valve  (2) move   to   the   left.      When   the   modulation   relief   valve moves to the left, it stops the flow of oil to the passages to torque converter (4) and PI pressure has an increase. As PI pressure becomes higher, the modulation relief valve moves to the right again and opens the  passages to  the  torque  converter.    This  higher  P1  pressure  also goes  through  the  orifice  to  the  right  of  load  piston  (3). The   higher   PI   pressure   on   the   load   piston,   plus   the spring force, makes the modulation relief  valve  move  to the  right  again  and  again  until  the  PI  pressure  is  at  a maximum.      The   modulation   relief   valve   controls   the maximum  pressure  by  letting  the  extra  pressure  go  to the   passage   for   the   torque   converter.      This   gradual increase   in   pressure   is   modulation.      The   modulation relief   valve   (2)   gives   modulation   for   all   the   clutches (speed and direction). The    differential    and    safety    valve    (6)    causes    a constant pressure difference of 50 psi (3.5 kg/cm2) (344 kPa)  less  than  the  PI  pressure  to  the  speed  clutches. This pressure difference lets the speed clutches become engaged    first,    and    then    the    direction    clutches    are engaged last.  When the PI pressure is at a maximum of approximately  3  10  psi  (21.80  kg/cm2)  (2137  kPa),  the P2 pressure is at approximately 160 psi ( 11.25 kg/cm2) (1103 kPa).  The shift is now complete. The   inlet   ratio   valve   (5)   controls   the   maximum   oil pressure to the torque converter.   P1  pressure  between the ratio valve and its slug keeps the valve closed.  The pressure of the oil that goes through the passage to the torque   converter   is   felt   by   the   end   of   the   ratio   valve opposite  the  slug.    When  the  pressure  of  the  oil  to  the torque converter is less than 1 15 psi (8.08 kg/cm2) (793 kPa), the ratio valve closes and the pressure oil goes to the torque converter. 2-95