H Y D R A U L I C  S Y S T E M TM    5-3805-258-24-1 T E S T I N G  A N D  A D J U S T I N G HYDRAULIC SYSTEM WARNING Hydraulic   oil,   under   pressure   that   can   be higher than 34500 kPa (5000 psi) can remain in the  hydraulic  system  on  this  machine  after  the engine and pump have been stopped. Sudden movement  of  the  machine  or  release  of  oil under pressure can cause injury to persons on or  near  the  machine.  To  prevent  possible  in- jury,  do  the  procedure  that  follows  before  test- ing and adjusting the hydraulic system: 1. 2. 3. 4. 5. 6. 7. 8. 9. Move the machine to a smooth horizontal loca- tion.  Move  away  from  working  machines  and personnel. Permit only one operator on the machine. Keep all   other   personnel   either   away   from   the machine or in view of the operator. Activate the parking brake. With the engine run- ning,  put  the  bucket  flat  on  the  ground.  When the  bucket  is  raised  for  tests  or  adjustments,  be sure that the bucket has correct support and the bucket is in the full dump position. The lift cir- cuit  has  high  oil  pressure  when  the  lift  arms raise  the  front  of  the  machine.  DO  NOT  STOP THE ENGINE with the front of the machine off of the ground. Install the anti-pivot link. Make   sure   all   hydraulic   pressure   is   released before   any   fitting,   hose   or   component   is loosened, tightened, removed or adjusted. Move the lift control lever to FLOAT position. Shut  off  the  engine. Move the lift control lever to the HOLD position. Carefully  loosen  the  filler  cap  on  the  hydraulic tank to release the pressure. 10. Carefully loosen plugs (1) at the rear of the tilt cylinder.  When  the  oil  from  the  loosened  plugs stops, tighten the two plugs. NOTE:  To  release  the  pressure  in  the  attachment cylinders,   carefully   loosen   two   large   plugs   near 11. Tighten the filler cap on the hydraulic tank. 12.  The  pressure  in  the  system  has  now  been released   and   lines   or   components   can   be removed. R E A R     O F     T I L T     C Y L I N D ER 1.    Plugs. During  a  diagnosis  of  the  hydraulic  system,  re- member that correct oil flow and pressure are neces- sary  for  correct  operation.  The  output  of  the  pump (oil flow) increases with an increase in engine speed (rpm)   and   decreases   when   engine   speed   (rpm)   is decreased. Oil pressure is caused by resistance to the flow of oil. Visual  checks  and  measurements  are  the  first  step when  troubleshooting  a  possible  problem.  Then  do the  Operation  Checks  and  last  the  Instrument  Tests. Use  the  5S5123  Hydraulic  Test  Group,  6V4161 Hydraulic  Test  Group,  a  stop  watch,  a  magnet,  a thermometer  and  a  mm  (inch)  ruler  for  basic  tests to  measure: 1. 2. The  pressure  of  the  oil  to  open  the  relief  valves for  the  main  and  pilot  systems  and  the  relief valves for the tilt circuits. Relief valve pressures that are too low will cause a decrease in the lift and the dig characteristics of the machine. Pres- sures  that  are  too  high  will  cause  a  decrease  in the  life  of  hoses  and  components. Drift  rates  in  the  lift  and  tilt  circuits:  Circuit drift is caused by a leakage past cylinder pistons, O-ring seals in the control valves, check valves or make-up valves that do not seat correctly or poor adjustment  or  fit  in  the  control  valves. plugs (1) at the top of the loader frame. When the oil from the loosened plugs stops, tighten the two large plugs. 4-67