How to Perform a Drive Pressure Check on a Caterpillar 943 Track Loader

[MikePhua]

The Caterpillar 943 and Its Hydrostatic Drive System
The Caterpillar 943 track loader, introduced in the 1980s, was part of Caterpillar’s mid-size hydrostatic loader lineup. It featured a hydrostatic transmission system, which uses hydraulic pressure to drive the machine rather than a mechanical gearbox. This system provides smooth, variable-speed control and excellent torque at low speeds, making it ideal for grading, loading, and site preparation. The hydrostatic drive relies on a closed-loop hydraulic circuit, where pressure and flow are precisely managed to control the travel motors on each track.
Why Drive Pressure Checks Matter
Over time, performance issues such as sluggish movement, uneven track response, or loss of power can arise. These symptoms often point to problems within the hydrostatic system—such as worn pumps, leaking hoses, or faulty control valves. A drive pressure check is a diagnostic procedure that helps isolate the root cause by measuring hydraulic pressure at key test ports.
Required Tools and Components
To perform a proper drive pressure check on the 943, you’ll need:

• A low-pressure hydraulic gauge (Caterpillar part number 8T0853, 0–60 psi range)
  
• High-pressure gauges (typically 0–6000 psi) for main loop pressure readings
  
• Hydraulic test hoses with quick-connect fittings compatible with the machine’s test ports
  
• A service manual or test and adjust guide (e.g., SENR3193) for port locations and pressure specs
  

Note that part number 8T0853 refers only to the gauge itself. It does not include hoses or fittings. Caterpillar does not offer a complete kit under a single part number; instead, technicians must assemble the necessary components individually.
Test Procedure Overview

1. Warm up the machine to operating temperature to ensure accurate readings.
   
2. Locate the drive pressure test ports—typically found near the hydrostatic pumps or on the travel motor lines.
   
3. Connect the appropriate gauge and hose to the port.
   
4. With the engine running at rated RPM, engage the travel lever in forward or reverse.
   
5. Record pressure readings under no-load and loaded conditions.
   
6. Compare readings to factory specifications.
   

Normal loop pressure for the 943 under load can exceed 5000 psi, while charge pressure (low-pressure side) should remain within 250–350 psi. A drop in charge pressure or excessive loop pressure fluctuation may indicate internal leakage or pump wear.
Common Findings and Interpretations

• Low charge pressure: May signal a clogged suction screen, weak charge pump, or internal leakage
  
• High loop pressure with poor travel: Could indicate a stuck swashplate or worn motor
  
• Uneven pressure between left and right circuits: Suggests imbalance in motor or pump performance
  

Additional Tips and Considerations

• Always bleed air from the system after connecting gauges to avoid false readings
  
• Use caution when working around high-pressure hydraulics—leaks can cause injection injuries
  
• If pressure readings are erratic, inspect the electrical control system for sensor or solenoid faults
  
• Keep a log of pressure readings over time to track wear trends and schedule preventive maintenance
  

Conclusion
Performing a drive pressure check on a Caterpillar 943 is a critical step in diagnosing hydrostatic drive issues. While the process requires specific tools and familiarity with the machine’s hydraulic layout, it can reveal valuable insights into system health. By interpreting pressure data accurately and comparing it to OEM specifications, technicians can pinpoint faults, reduce downtime, and extend the life of this dependable track loader. In the world of heavy equipment, pressure tells a story—and knowing how to read it is key to keeping machines moving.