Troubleshooting Brake Failure on VOLVO EC360 Excavator

[MikePhua]

       

Introduction
Brake failure on excavators can be subtle at first but quickly escalate into severe operational risks. One VOLVO EC360 excavator, after reaching 3,000 working hours, began exhibiting insufficient braking on the upper turntable. Initially, the swing would not stop immediately during rotation. After two more hours of operation, the issue worsened significantly. Slow rotation required reversing over 90 degrees to halt, while fast rotation forced the swing to continue a short distance in the same direction before stopping. This case highlights the critical need for systematic diagnosis and maintenance of hydraulic swing motors and brake systems.
Fault Analysis
The primary symptom indicated insufficient braking force. Multiple potential causes were systematically investigated:
1. Brake Pad Wear and Spring Force

• Test: The excavator was parked on a slope, with the upper turntable perpendicular to the incline. Engine was turned off; the swing did not roll downhill due to gravity.
  
• Procedure: Pilot valve was operated while the engine ran; the turntable could not rotate.
  
• Conclusion: Brake pads and springs were intact, ruling out wear or insufficient spring tension.
  

2. Leakage or Pilot Valve Issues

• Possible causes included: pilot valve not returning correctly, directional valve wear allowing hydraulic oil to bypass into the brake circuit, or other leaks in lines such as AM, A1, A13, and Psp.
  
• Test: Pressure measurement at SH(A12) during and after pilot valve operation. Pressure dropped from 3.6 MPa to 0 after releasing the valve.
  
• Conclusion: No abnormal leakage or valve malfunction was detected.
  

3. Throttle Valve or Brake Control Valve Malfunction

• Concern: Blockage in the throttle valve or brake control valve stuck in the engaged position could prevent pressure release, leaving the brake inactive.
  
• Test: Pressure in the brake piston chamber dropped from 3.6 MPa to 0 within approximately 3 seconds after releasing the pilot valve. However, the swing still failed to stop.
  
• Conclusion: Both the throttle and brake control valves were functioning normally.
  

4. Swing Motor Wear

• Observations: Swing motor oil provides hydraulic braking alongside mechanical brake pads. Wear in pistons, slippers, or distribution plates can destroy the oil film necessary for hydraulic braking. Leaks reduce braking efficiency.
  
• Conclusion: The primary focus shifted to the swing motor, as it likely caused delayed stopping during rotation.
  

Fault Resolution
1. Pressure Tests and Initial Diagnosis

• Maximum pressure measured at swing motor start: 16 MPa required to initiate rotation (high resistance).
  
• Maximum pressure under load: 20 MPa, lower than standard 26 MPa.
  
• Indication: Excessive internal resistance and wear.
  

2. Inspection of Swing Motor

• Removing the discharge filter revealed significant metallic debris.
  
• Disassembly showed:
  • Numerous metal shavings inside the motor
    
  • Scratches on distribution plate surfaces
    
  • Extruded seals behind distribution plates
    
  • Visible damage on piston slippers, swash plates, and nine-hole plates
    
  • Lower bearing surface with severe metal loss
    

3. Root Cause

• Measured bearing height: 29.7 mm vs. standard 29.0 mm
  
• Faulty installation: Oversized or incorrect bearings created excessive radial load, leading to abnormal wear.
  
• Metal debris caused additional scoring on mating surfaces, worsening performance.
  

4. Repair Actions

• Replaced bearings with standard, correctly sized units
  
• Manually polished: piston slippers, distribution plates, swash plates, and nine-hole plates
  
• Cleaned hydraulic lines and oil tank
  
• Replaced hydraulic filters and hydraulic oil
  
• After reassembly and test operation, the brake failure was resolved completely
  

Recommendations for Prevention

• Regular inspection of swing motor components every 2,000–2,500 hours, focusing on piston slippers, distribution plates, and seals
  
• Maintain clean hydraulic fluid and replace filters at recommended intervals
  
• Monitor swing motor pressure to detect early resistance increases
  
• Ensure correct bearing selection and installation, avoiding excessive axial or radial loads
  
• Train operators to detect abnormal swing behavior early, such as delayed stopping or unusual resistance
  

Key Terminology

• Pilot Valve: Controls hydraulic flow to the main actuator or brake system
  
• Throttle/Control Valve: Regulates oil flow to maintain proper braking force
  
• Swing Motor: Hydraulic motor driving upper structure rotation, provides both motion and hydraulic braking
  
• Swash Plate: Converts piston reciprocation into rotary motion
  
• Slippers/Pistons: Components within the motor responsible for force transmission via hydraulic pressure
  
• Nine-Hole Plate: Component distributing hydraulic fluid to pistons in the swing motor
  

Case Note
This repair demonstrates how seemingly minor internal wear, such as incorrectly installed bearings, can progressively compromise hydraulic braking. Early detection through pressure monitoring and scheduled maintenance prevents severe downtime and potential safety hazards. Operators often underestimate subtle swing irregularities until failure becomes significant, emphasizing proactive diagnostics.
Would you like me to create a diagram showing the pressure flow and braking circuit for EC360? It would make these steps visually clearer.