Swing Brake Failure on Komatsu PC60-6 and Field Repair Strategies

[MikePhua]

The Komatsu PC60-6 and Its Legacy in Compact Excavation
The Komatsu PC60-6 hydraulic excavator was introduced in the late 1980s as part of Komatsu’s push into the compact-to-mid-size excavator segment. With an operating weight of approximately 13,000 pounds and powered by a Komatsu 4D95L diesel engine producing around 55 horsepower, the PC60-6 was designed for utility trenching, small-scale earthmoving, and forestry work. Its popularity surged in Southeast Asia, North America, and island construction projects due to its balance of maneuverability and durability.
Komatsu, founded in 1921 in Japan, had by the 1990s become the world’s second-largest construction equipment manufacturer. The PC60 series sold tens of thousands of units globally, with the -6 variant known for its mechanical simplicity and robust hydraulic system. However, as these machines aged, certain components—especially the swing brake system—began to show vulnerabilities under field conditions.
Swing Brake Symptoms and Island Project Breakdown
One operator reported that after replacing seals in the swing gear assembly, swing motor, and travel planetary system, the machine operated normally for a week. But during excavation on a remote island, the swing brake suddenly engaged mid-swing, locking the upper structure sideways and rendering the machine immobile.
Key symptoms included:

• Rapid clicking from the swing brake solenoid
  
• Twitching of the two small hydraulic hoses connected to the swing motor
  
• Engine bogging under swing input, indicating hydraulic resistance
  
• Bypass switch for the swing brake no longer functioning
  

Terminology:

• Swing Brake: A hydraulic or mechanical system that locks the upper structure of an excavator to prevent rotation when parked or during transport.
  
• Solenoid Valve: An electrically actuated valve that controls hydraulic flow to engage or release the swing brake.
  
• Bypass Switch: A manual override that allows operators to disable the swing brake under certain conditions.
  

The operator suspected that hydraulic pressure normally releases the swing brake, and that a failure in the solenoid or electrical circuit was preventing pressure from reaching the brake actuator.
Starter Failure and Electrical System Vulnerabilities
Compounding the issue, the starter motor began to fail intermittently. The operator had to tap the starter while someone held the key in the “start” position to get the engine running. The dealer quoted $2,200 for a replacement starter and $1,400 for a swing brake solenoid—prices that prompted the operator to seek aftermarket alternatives.
Suggested electrical checks:

• Measure voltage at the solenoid plug (should be 24V)
  
• Test solenoid coil resistance using a multimeter (typical range: 20–40 ohms)
  
• Inspect master relay near the battery for voltage drop
  
• Monitor system voltage during operation to detect fluctuations
  

Terminology:

• Master Relay: A high-current relay that distributes power to critical systems when the ignition is on.
  
• Voltage Drop: A reduction in voltage due to resistance or poor connections, often causing erratic behavior in solenoids and sensors.
  

In Tennessee, a forestry operator noted similar symptoms on a PC200LC-6. Replacing the starter solenoid and cleaning the contact plate restored reliable starting. He emphasized that low voltage can cause solenoids to click rapidly without fully engaging, leading to partial brake release and erratic swing behavior.
Solenoid Removal and Aftermarket Sourcing
Removing the swing brake solenoid involves unscrewing a plastic nut on the rear side of the valve block. The solenoid is seated with an O-ring and may require gentle prying to extract. Once removed, it can be taken to a hydraulic shop for matching or rebuilt if the coil is intact.
Recommended steps:

• Disconnect battery before removal
  
• Label and photograph wiring for reassembly
  
• Inspect solenoid for heat damage or magnet wear
  
• Replace O-ring during reinstallation to prevent leaks
  

Aftermarket sourcing tips:

• Search for “PC60-6 swing brake solenoid” or “magnet solenoid”
  
• Use part numbers from the service manual to cross-reference
  
• Check industrial suppliers and hydraulic component rebuilders
  
• Consider solenoids from PC60-5 models if compatible
  

In Ontario, the operator eventually found a compatible solenoid online for $222, a fraction of the dealer price. He noted that COVID-era supply chain disruptions had made sourcing parts more difficult, with many listings removed from major platforms.
Bypassing the Swing Brake and Safety Considerations
While bypassing the swing brake solenoid is technically possible by applying constant hydraulic pressure to the brake actuator, this approach is not recommended for long-term use. It eliminates the ability to lock the upper structure during transport or maintenance, posing safety risks.
Safer alternatives:

• Install a manual hydraulic valve to control brake pressure
  
• Use a toggle switch with relay to simulate solenoid function
  
• Add a pressure gauge to monitor brake circuit status
  

Terminology:

• Manual Hydraulic Valve: A lever-operated valve that allows direct control of fluid flow without electronics.
  
• Relay-Controlled Switch: An electrical switch that uses a relay to handle high current loads safely.
  

In British Columbia, a contractor retrofitted his PC60-6 with a manual valve for swing brake control after repeated solenoid failures. He trained his crew to engage the brake manually during transport and disable it during operation, restoring functionality without relying on electronics.
Conclusion
The Komatsu PC60-6 remains a reliable excavator, but swing brake failures can immobilize the machine in critical moments—especially on remote projects. Through methodical electrical diagnostics, solenoid testing, and creative retrofitting, operators can restore swing function and avoid costly downtime. Whether stranded on an island or clearing land in the interior, understanding the interplay between hydraulic pressure, solenoid control, and electrical integrity is key to keeping the PC60-6 moving.