Komatsu PC35MR-2 Hydraulic Troubleshooting and System Reliability

[MikePhua]

The PC35MR-2’s Role in Compact Excavation
The Komatsu PC35MR-2 is a compact hydraulic excavator designed for tight-access jobsites, utility trenching, and landscaping. Introduced in the early 2000s, it features a zero-tail swing design, allowing full rotation within the track width—ideal for urban and residential projects. With an operating weight around 8,000 pounds and a 28–30 horsepower engine, the PC35MR-2 balances maneuverability with digging power.
Komatsu, founded in 1921 in Japan, has long been a leader in hydraulic excavator technology. The MR series was developed to meet growing demand for compact machines with full-function hydraulic systems. Sales data from 2024 shows that over 60,000 units of the PC35MR series have been sold globally, with strong adoption in North America, Europe, and Southeast Asia.
Understanding the Hydraulic Architecture
The PC35MR-2 uses a load-sensing hydraulic system powered by a gear-type or variable-displacement pump. This system adjusts flow and pressure based on operator input and load demand, improving efficiency and control. Key components include:

• Main Hydraulic Pump: Supplies pressurized fluid to all actuators.
  
• Control Valves: Direct flow to boom, arm, bucket, and travel motors.
  
• Pilot Circuit: Low-pressure system that actuates main valves via joystick input.
  
• Hydraulic Tank and Filters: Store and clean fluid before recirculation.
  
• Travel Motors: Propel the machine via hydraulic drive.
  

Terminology note:

• Spool Valve: A sliding valve that opens or closes fluid paths based on joystick position.
  
• Relief Valve: Prevents overpressure by diverting excess fluid.
  
• Cavitation: Formation of vapor bubbles due to low pressure, which can damage pump components.
  

The system is designed to operate at pressures up to 3,000 psi, with flow rates tailored to each function. Smooth operation depends on clean fluid, accurate valve response, and proper sensor feedback.
Common Hydraulic Problems and Field Symptoms
Operators may encounter several hydraulic issues over time:

• Slow or weak boom and arm movement
  
• Jerky or uneven travel response
  
• Hydraulic fluid overheating during extended use
  
• Audible whining or pump cavitation
  
• Inconsistent joystick response or dead zones
  

In one case, a contractor in Florida noticed that his PC35MR-2 would stall during travel while lifting. The issue was traced to a clogged pilot filter, which restricted signal pressure and caused valve lag. Replacing the filter and flushing the pilot circuit restored full responsiveness.
Another technician in British Columbia found that the travel motors were sluggish. After testing, the main pump was found to be underperforming due to internal wear. Installing a remanufactured pump and recalibrating the relief valves resolved the issue.
Diagnostic Steps and Inspection Tips
To troubleshoot hydraulic problems:

• Check fluid level and condition—look for contamination, foaming, or discoloration
  
• Inspect filters and screens for blockage or metal particles
  
• Test pilot pressure at control valve input ports
  
• Measure main pump output using flow meters and pressure gauges
  
• Inspect hoses and fittings for leaks, abrasion, or collapse
  
• Verify joystick signal continuity and valve spool movement
  

Recommended service intervals:

• Hydraulic fluid change: every 1,000 hours or annually
  
• Filter replacement: every 500 hours or semi-annually
  
• Hose inspection: monthly or every 100 hours
  
• Pilot circuit flush: every 2,000 hours or during major service
  

One fleet manager in Texas added a magnetic drain plug to his PC35MR-2 hydraulic tank, allowing early detection of pump wear through metal particle collection.
Repair Procedures and Component Replacement
When repairing hydraulic faults:

• Always depressurize the system before disassembly
  
• Use OEM or high-quality aftermarket seals and filters
  
• Torque fittings to manufacturer specs to prevent leaks
  
• Replace fluid with compatible ISO VG 46 or VG 68 hydraulic oil
  
• Calibrate relief valves using factory procedures and test equipment
  

If replacing the main pump:

• Match flow rate and pressure specs precisely
  
• Flush all lines and cylinders before installation
  
• Prime the pump with clean oil to prevent dry start
  
• Test system under load and monitor temperature and response
  

Some operators retrofit auxiliary hydraulic kits for thumb or breaker use. These must be plumbed with proper flow restrictors and return lines to avoid overloading the system.
Design Evolution and Manufacturer Insights
Later Komatsu models, such as the PC35MR-5, introduced electronic control modules and improved diagnostics. These systems monitor pump output, valve position, and joystick input in real time, allowing faster troubleshooting and better fuel efficiency.
Komatsu’s KOMTRAX telematics platform provides remote monitoring of hydraulic performance, alerting owners to pressure anomalies, fluid temperature spikes, and service intervals. These features reduce downtime and improve fleet management.
Sales trends show increased demand for compact excavators with advanced hydraulic control, especially in urban infrastructure and utility sectors. The PC35MR-2 remains popular due to its mechanical simplicity and field-repairability.
Conclusion
Hydraulic problems in the Komatsu PC35MR-2 can be frustrating, but with methodical diagnostics and proper maintenance, they are often solvable without major overhaul. From pilot pressure to pump output, each part of the system plays a role in smooth operation. With clean fluid, calibrated valves, and responsive controls, this compact excavator continues to deliver precision and power—digging deep, even in tight spaces.