Diagnosing Slow Track Movement in the Caterpillar 973: Causes, Symptoms, and Solutions

[MikePhua]

Understanding the Caterpillar 973 Track-Type Loader
The Caterpillar 973 is a mid-to-large track-type loader known for its heavy-duty capabilities in material handling, grading, and land clearing. With a hydrostatic drive system and robust undercarriage, it’s built to move large volumes efficiently. However, when the track movement begins to slow or becomes unresponsive, the machine's productivity and reliability can be significantly compromised.
A common complaint among 973 operators is sluggish track performance, especially under load or during directional changes. This issue often points to a combination of hydraulic, mechanical, or electrical faults—each requiring careful diagnosis.
Key Symptoms of Slow Track Movement
Operators typically report the following behaviors:

• One track moving slower than the other or hesitating.
  
• Both tracks slowing down under load, especially uphill.
  
• Machine stalling during turns.
  
• Transmission becoming hot after short periods of operation.
  
• Lag between joystick input and track response.
  
• Audible whining or chatter from the hydraulic system.
  

These symptoms may occur intermittently or progressively worsen, often masked at first by operator compensation through throttle and steering adjustments.
Potential Root Causes
Slow track movement in a 973 can arise from various system-level issues. These include:

• Hydrostatic Transmission Faults
  The 973 uses a hydrostatic drive, where each track is driven by a variable-displacement pump and motor system. If there’s a loss of pressure, internal leakage, or a malfunctioning swash plate actuator, power delivery to the track will degrade.
  
• Drive Motor Wear
  The final drive motor for each track can develop internal bypassing or bearing wear, reducing torque output.
  
• Case Drain Overflow
  Case drain filters may be clogged, or internal motor leakage may cause excessive case pressure. This restricts fluid return and limits performance.
  
• Contaminated Hydraulic Fluid
  Water or debris in the hydraulic system can cause cavitation and erratic behavior. In some cases, moisture leads to corrosion inside control valves or pump chambers.
  
• Electronic Control Module (ECM) Faults
  If the control system is not receiving or sending proper signals to the drive pump solenoids or pressure sensors, power distribution between tracks may become uneven or restricted.
  
• Sticking Proportional Control Valves
  Dirt or varnish buildup in the hydrostatic drive control valves can cause delayed or incomplete actuation.
  
• Track or Undercarriage Resistance
  Seized track rollers, misaligned idlers, or tight tensioners can add mechanical drag, creating an imbalance between power demand and available torque.
  

Diagnostic Procedures
To troubleshoot slow track issues, technicians typically follow this sequence:

• Visual Inspection
  Check for fluid leaks, loose hoses, and damaged electrical connectors near the hydrostatic pumps, control valves, and motor assemblies.
  
• Hydraulic Pressure Testing
  Install gauges at test ports on the drive pump and motors. Compare pressures against CAT specifications under various operating conditions.
  
• Case Drain Flow Measurement
  Measure return flow volume to detect internal leakage in the track motors. Excessive flow indicates worn internal components.
  
• ECM Diagnostics
  Use Caterpillar’s ET (Electronic Technician) tool to scan for fault codes related to propulsion, joystick calibration, and sensor feedback.
  
• Undercarriage Inspection
  Manually rotate each track and look for abnormal resistance. Check sprockets, track tensioners, rollers, and idlers.
  
• Temperature Scanning
  Use a thermal camera or infrared gun to compare heat buildup in the pumps and motors. Uneven heat distribution may point to internal friction or hydraulic dead-heading.
  

Real-World Example: The Muddy Solution
A contractor operating a 973 in South Carolina noticed that the left track was lagging significantly during turns. Initial suspicion fell on the hydraulic pump, but deeper investigation revealed a seized bottom roller packed with mud and debris. The increased drag on the left side misled the hydrostatic control system, causing a false torque load and reducing the response rate. After cleaning and replacing the roller bearing, normal operation resumed—saving the owner thousands in unnecessary pump replacement.
Case Study: Electrical Glitch Triggers Power Loss
In another case, a 973 was reported to “crawl” in both forward and reverse despite normal engine performance. Technicians found that a faulty ground wire near the hydrostatic pump control solenoid was intermittently cutting signal to the drive ECM. A simple electrical continuity test uncovered the issue. Once repaired, the machine returned to full function. This highlights the importance of verifying wiring integrity alongside mechanical inspections.
Preventive Measures and Maintenance Tips
To avoid recurring slow track issues, consistent preventive maintenance is essential:

• Hydraulic System Care
  • Replace hydraulic fluid and filters at manufacturer-specified intervals.
    
  • Test fluid samples for contamination or breakdown.
    
  • Regularly inspect and clean case drain filters.
    
• Electrical System Monitoring
  • Secure and insulate wiring harnesses near moving components.
    
  • Periodically scan ECMs for dormant or intermittent fault codes.
    
• Undercarriage Service
  • Grease rollers and idlers regularly.
    
  • Maintain correct track tension, especially in muddy or cold climates.
    
  • Remove accumulated debris from undercarriage compartments.
    
• Operator Best Practices
  • Avoid aggressive directional changes at high RPMs.
    
  • Let the machine warm up before engaging the tracks under load.
    
  • Report unusual sounds or behavior early for prompt inspection.
    

Conclusion
Slow track movement in the Caterpillar 973 can stem from a wide spectrum of mechanical, hydraulic, or electronic issues. Accurate diagnosis depends on a structured inspection process and an understanding of how hydrostatic systems integrate with electronic controls and mechanical resistance. In many cases, what appears to be a major system failure can be traced back to something as simple as a clogged filter or electrical short.
By investing in regular maintenance and responding quickly to early warning signs, operators and fleet managers can extend the life of these high-value machines and prevent costly downtime. In heavy equipment, as in medicine, early intervention makes all the difference.