TM 5-3895-383-24 Illustration 76 Location of Pressure Taps and Plugs (1) Pressure tap.  (2) Pressure tap.  (3) Two plugs (X1 and X2). (4) Balance lines. 1. Remove plugs (3) and connect a jumper hose between the X1 and X2 ports.  This makes equal oil pressure on each side of the servo piston. 2. Disconnect one end of each balance line (4).  Plug the balance lines and cap the fittings for the balance lines. 3. Connect two 60000 kPa (8700 psi) pressure gauges to pressure taps (1) and (2). 4. With  the  speed  range  switch  in  LOW  SPEED  range, start and run the engine at 1200 rpm. 5. Look at the pressure gauges.  The pressures on the two gauges should be equal. Illustration 77 Servo Valve (Piston Pump) (5) Locknut. 6. If   is   necessary   to   adjust   the   neutral   position   of   the piston, loosen locknut (5).  Use an allen wrench to turn the  servo  valve  neutral  adjustment  screw.    Turn  the screw  clockwise  or  counterclockwise  in  order  to  adjust the  mechanical  center  of  the  servo.    The  pressure  on the  gauges  should  change.    Adjust  the  screw  until  the two pressures are equal. 7. Stop the engine.  Remove the two 60000 kPa (8700 psi) gauges.    Replace  the  gauges  with  two  4000  kPa  (580 psi) gauges. 8. Repeat Steps 4 through 6. 9. Tighten locknut (5).  Remove all of the test equipment. Install plugs (3). 10. Remove   the   caps   and   the   plugs.      Reconnect   the balance lines (4). NOTE: Perform  this  procedure  on  the  axle  propel  pump in   the   same   manner.      Remove   the   plugs   and install the jumper hose on the servo from the axle propel  pump.    Read  the  measurements  from  the pressure taps that are on the axle propel pump. TrueTrac Differential - Test SMCS Code:  3263-081; 3265-081 1. Check   that   the   wheels   on   the   axle   of   the   TrueTrac differential  are  driving.    Make  this  test  under  load,  so that engine torque is applied through the differential with the wheels on the ground.  One way to achieve this load is to drive up to a solid, stationary object on a dirt or on a  gravel  surface.    When  the  machine  is  against  the stationary     object,     the     load     can     be     achieved     by attempting   to   spin   the   wheels.      Perform   this   test   in forward and reverse. NOTICE Do not operate the machine if both wheels of the TrueTrac differential equipped axle are not driving. 2. Drive the machine in a tight circle.  Make sure that the machine is on a flat surface with good traction.  Perform this turn in forward and reverse in order to be sure that the outside wheel does not scuff the ground. NOTE: The TrueTrac differential should not be disassembled.  If the differential is disassembled, the proper concentricity and the proper tolerances may not be retained. 3. The  TrueTrac  differential  must  be  replaced  if  either  of the wheels do not operate freely. 10-71