Hitachi 120-3 class Operator's Manual page 310

Problem
Travel is Not Smooth
Swing Does Not Work
Swing is Not Smooth
Engine Stops When Travel or/
and Control Lever Moved
TROUBLESHOOTING
HYDRAULIC SYSTEM
Cause
Rocks or mud "jammed" in track frame
Travel brake not releasing
Swing brake release valve
Swing motor
Pilot valve
Swing gear
Swing bearing
Lack of grease
Combination valve
Failure of connector contact
Failed wiring harness
Failed Main controller
11-12
Solution
Remove and repair.
See your authorized dealer.
See your authorized dealer.
See your authorized dealer.
See your authorized dealer.
See your authorized dealer.
See your authorized dealer.
Apply grease.
See your authorized dealer.
Repair or replace.
See your authorized dealer.
See your authorized dealer.