Hitachi ZAXIS 120-6 class Operator's Manual page 473

Swing Function
Problem
Upperstructure does not swing.
Swing is not smooth.
Just after the control valve, swing motor relief valve and/or the swing motor is replaced, a noise may be emitted and/or
operation may not be performed smoothly due to air trapped in the hydraulic line.
Slowly continue to operate the machine for approx. 10 minutes to bleed air.
After repair work is complete, be sure to check the oil level in the hydraulic oil tank. Refill hydraulic oil as needed.
TROUBLESHOOTING
Cause
Faulty swing parking brake
Faulty swing parking brake release valve
Broken swing motor
Faulty pilot valve
Faulty pilot circuit line
Worn swing gear
Damaged swing bearing and bearing balls.
Lack of grease
Inversion protective valve
11-7
* Repair or replace
* Repair or replace
* Repair or replace
* Replace
* Repair or replace
* Repair or replace
* Repair or replace
Refill
* Repair or replace
Items with * mark: Consult your authorized dealer.
Solution