TRUCK SERVICE MANUAl   TM5-4210-230-14&P-1 STEERING DESCRIPTION The   housing   and   internal   parts   of   the  pump   are inside the reservoir so that the pump parts operate submerged in  oil.    The  reservoir  is  sealed  against  the  pump  housing, leaving  the  housing  face  and  the  shaft  hub  exposed.    The reservoir has a filler neck fitted with a cap.  On the 125 series pump, a shaft bushing and seal are pressed into the housing from  the  front.    The  drive  shaft  is  inserted  through  this  seal and bushing.  On the 235 series pump, the shaft is supported in the front with a ball bearing and in the back with a needle bearing.  The drive shaft seal is pressed into the housing and located behind the ball bearing.  A large hole in the rear of the housing   contains   the   functional   parts;   namely   ring,   rotor, vanes  and  plates.    A  smaller  hole  contains  the  control  valve assembly and spring. The thrust plate (Figs.  1 & 2) is located on the inner face  of  the  housing  by  two  dowel  pins.  This  plate  has  four central  blind  cavities  for  undervane  oil  pressure.    The  two outer blind cavities direct discharge oil through the two cross- over  holes  in  the  pump  ring  (Fig.    3),  through  the  pressure place and into cavity 1 (Fig.  4).  The two outside indentations in the thrust plate are for intake of the oil from the suction part of the pump. The pump ring (Fig.  3) is a plate having the mating surfaces  ground  flat  and  parallel.    The  center  hole  is  a  two- lobed cam in which the rotor and vanes operate.  The ring is placed  next  to  the  thrust  plate  and  located  with  the  same dowel pins. Fig.  3 Pump Ring and Rotor The   pressure   plate   is   fitted   against   the   ring   and located   with   the   same   two   dowel   pins.   This   plate   has   six through  ports.    The  four  central  through  ports  connect  from cavity  1  (Fig.    4)  to  supply  undervane  oil  pressure.    The  two outer ports pass oil under discharge pressure to cavity 1.  The two indentations are for oil intake from the suction part of the pump, cavity 6 (Fig.  5) into the rotor. The   reservoir   is   for   oil   storage.      It   receives   and directs  the  return  oil  back  to  the  make-up  passage  of  the pump. The   drive   shaft   is   fitted   with   a   pulley   and   is   belt driven from the crankshaft.  The rotor is loosely splined to the drive  shaft  and  secured  with  a  retaining  ring.    It  is  located centrally within the ring and between the thrust and pressure plates. The ten vanes are mounted in radial slots in the rotor (Fig.  3). OPERATION The mode of operation of the power steering pump is based  upon  the  demand  of  the  power  steering  system.    The various    major    modes    of    operation    are:    slow    cornering, moderate to high speed straight ahead driving, and cornering against  the  wheel  stop.    The  pump  is  designed  to  recognize these  conditions  as  required  by  the  steering  gear  valve  and compensate for them internally. As the drive shaft turns the rotor, the vane tips follow the inner cam surface of the pump ring, moving outward and inward    twice    during    each    revolution.        This    results    in    a complete  pumping  cycle  every  180  degrees  of  rotation  (Fig. 3).  Oil  is  moved  in  the  spaces  between  the  vanes.    As  the vane   tips   move   outward,   oil   is   sucked   into   the   inter-vane spaces  through  four  suction  ports  in  the  pressure  and  thrust plates.      The   pressure   of   the   oil   is   raised,   and   the   oil   is discharged from the pump ring, as the vane tips move inward. High  pressure  oil  discharges  into  cavity  1,  (Fig.    4),  through two  open  ports  in  the  pressure  plate,  and  through  two  blind ports  in  the  thrust  plate,  which  are  connected  to  cavity  1  by the   cross-over   holes   in   the   ring.      A   portion   of   this   oil   is circulated   through   the   central   port   system   in   the   pressure plate, forcing the vanes to follow the cam surface of the ring. The  ring-rotor  leakage  oil  12  (Fig.    4)  is  used  for  bushing lubrication and then bled to the reservoir. SLOW CORNERING (FIG.  4) During  slow  cornering  maneuvers,  the  oil  pressure required  will  usually  not  exceed  2760  kilopascals  (400  PSI) RPM   of   the   pump   is   not   high   enough   to   require   internal bypassing   of   oil;   therefore,   the   pump   bypass   port   to   (5) remains closed. CTS-2296R  Chapter 1, Page 3 PRINTED IN UNITED STATES OF AMERICA