TM 5-3825-226-24 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  P1  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 P1 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  P1 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).  P1 pressure also goes through the orifice to  the  right  of  load  piston  (3).    The  Pi  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 P I1 pressure has an increase. As  P1  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  310  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.    PI  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 115 psi (8.08 kg/cm²) (793 kPa), the ratio valve closes and the pressure oil goes to the torque converter. 2-93