Why Does the JD 655C Series II Occasionally Drift Left

[MikePhua]

Overview of the JD 655C Series II Crawler Loader
The John Deere 655C Series II is a mid-sized crawler loader introduced in the early 2000s, designed for earthmoving, demolition, and utility work. With an operating weight of approximately 38,000 lbs and powered by a John Deere 6068T turbocharged diesel engine producing around 145 horsepower, the 655C combines robust traction with responsive hydrostatic drive. Its Series II upgrade included improved operator controls, enhanced diagnostics, and refined hydraulic modulation.
The machine uses a dual-path hydrostatic transmission, meaning each track is independently powered by its own hydraulic circuit. This design allows for precise steering and variable speed control but also introduces complexity in diagnosing tracking issues.
Symptoms of Intermittent Left Drift
Operators have reported that the 655C occasionally pulls to the left while traveling forward or reverse, even when not under load. The drift typically lasts a few minutes before self-correcting. There is no loss of pushing power, and the issue does not appear to be terrain-related.
This behavior suggests a temporary imbalance in hydraulic output between the left and right drive motors. Because the machine uses electronic sensors and control valves to regulate flow, even minor inconsistencies can cause directional drift.
Possible Causes and Diagnostic Path
Several factors may contribute to intermittent tracking drift:

• Sensor calibration drift: The hydrostatic system relies on position sensors and pressure transducers. If a sensor begins to misreport values due to age or electrical interference, the control module may reduce flow to one side.
  
• Electrical grounding issues: Poor grounding or corroded connectors can cause erratic signals to the transmission controller. This is especially common in older machines exposed to moisture or vibration.
  
• Valve spool sticking: Hydraulic control valves may stick intermittently due to contamination or wear, causing uneven flow distribution.
  
• Software calibration: The Series II models include onboard diagnostics and calibration routines. If the system has not been recalibrated after component replacement or service, drift may occur.
  

A technician in Georgia once encountered a similar issue with a 655C that pulled left during cold starts. After checking the electrical harness and cleaning the ground terminals, the problem disappeared—suggesting that electrical noise was interfering with sensor readings.
Recommended Troubleshooting Steps
To isolate and resolve the issue:

• Run system diagnostics using the onboard monitor or external service tool. Look for sensor faults or calibration errors.
  
• Inspect wiring harnesses, especially near the transmission controller and drive motors. Clean and tighten all ground points.
  
• Check hydraulic fluid condition. Contaminated or aerated fluid can affect valve response.
  
• Perform a calibration cycle. Follow the manufacturer’s procedure to reset sensor baselines and valve timing.
  
• Test drive motors independently. Use flow meters to compare output under load and at idle.
  

If the issue persists, consider replacing the affected sensor or valve block. In rare cases, the transmission controller may require reprogramming or replacement.
Preventive Maintenance and Long-Term Solutions
To prevent future tracking issues:

• Flush hydraulic system every 1,000 hours, replacing filters and inspecting for metal particles.
  
• Protect electrical connectors with dielectric grease and weatherproof boots.
  
• Update software if newer calibration profiles are available from John Deere.
  
• Avoid prolonged idling, which can cause uneven thermal expansion in hydraulic components.
  

Conclusion
Intermittent left drift in the JD 655C Series II is typically caused by sensor miscalibration, electrical interference, or minor hydraulic imbalance. While the machine’s dual-path hydrostatic system offers excellent control, it also demands precise input and clean signals. With proper diagnostics and preventive care, the 655C can continue delivering reliable performance across a wide range of job sites.