Troubleshooting Tracking Failure on a Case 850K Dozer

[MikePhua]

The Case 850K and Its Evolution
The Case 850K crawler dozer was introduced in the early 2000s as part of Case Construction Equipment’s K-series lineup, designed to offer improved hydrostatic drive control, enhanced operator ergonomics, and simplified diagnostics. Case, founded in 1842, had already built a reputation for durable earthmoving machines, and the 850K continued that legacy with a mid-size platform ideal for grading, site prep, and forestry work.
Equipped with a 6.7-liter turbocharged diesel engine and dual-path hydrostatic transmission, the 850K offered precise maneuverability and variable speed control. Its electronic control system allowed operators to adjust tracking sensitivity and response through onboard settings, making it a favorite among contractors working in variable terrain.
Symptoms of Tracking Loss
A common issue reported on the 850K involves the machine initially moving normally when the joystick is engaged, but gradually slowing down until it stops completely. This behavior occurs even when the tracking percentage is set to 100%, suggesting that the issue is not due to operator settings but rather a deeper mechanical or electrical fault.
Typical symptoms include:

• Normal movement for the first few seconds after joystick engagement
  
• Progressive loss of speed despite throttle input
  
• Complete halt with joystick still in forward position
  
• No fault codes displayed on the monitor
  
• History of electrical issues in unrelated systems
  

This pattern points toward a failure in the hydrostatic control loop, possibly involving sensor feedback, solenoid response, or hydraulic pressure regulation.
Hydrostatic Drive and Electronic Control Interface
The 850K uses a dual-path hydrostatic transmission, meaning each track is powered by its own hydraulic circuit. The joystick sends electronic signals to proportional control valves, which modulate pump displacement and motor speed. The system relies on feedback from speed sensors, pressure transducers, and joystick potentiometers to maintain consistent movement.
Key components include:

• Joystick controller with integrated potentiometer
  
• Electronic Control Module (ECM) governing drive logic
  
• Proportional solenoids controlling hydraulic flow
  
• Speed sensors on each final drive
  
• Pressure sensors on pump output lines
  

If any of these components fail or provide erratic data, the ECM may reduce drive output as a protective measure, resulting in the observed slowdown and eventual halt.
Diagnostic Path and Electrical Inspection
To isolate the issue, technicians should begin with a full scan of the ECM using Case’s diagnostic software. If no fault codes are present, manual inspection is required:

• Check voltage output from joystick potentiometer during movement
  
• Inspect wiring harness for chafing, corrosion, or loose connectors
  
• Test solenoid resistance and actuation response
  
• Verify hydraulic pressure at each pump outlet using a calibrated gauge
  
• Confirm sensor feedback matches expected values under load
  

In one documented case, a technician found that a corroded ground wire near the battery box was causing intermittent voltage drops to the ECM. Once cleaned and re-secured, the machine resumed normal tracking behavior.
Mechanical Possibilities and Hydraulic Contamination
If electrical systems check out, mechanical issues may be at play. Potential causes include:

• Internal leakage in hydrostatic pumps or motors
  
• Contaminated hydraulic fluid causing valve sticking
  
• Worn pump swash plates reducing displacement
  
• Air ingress into the hydraulic circuit
  

Hydraulic fluid analysis can reveal contamination levels, including water, metal particles, and varnish. If contamination is found, a full system flush and filter replacement is recommended. Case specifies hydraulic fluid change intervals of 1,000 hours, but machines operating in dusty or wet environments may require more frequent service.
Preventative Measures and Software Calibration
To prevent future tracking issues:

• Perform ECM software updates as released by Case
  
• Calibrate joystick response annually using diagnostic tools
  
• Replace hydraulic filters every 500 hours
  
• Inspect wiring harnesses quarterly for wear
  
• Maintain fluid cleanliness with magnetic drain plugs and sampling
  

Operators should also avoid abrupt joystick movements, which can stress the hydrostatic system and trigger protective slowdowns. Smooth input allows the ECM to modulate flow more effectively and maintain consistent tracking.
A Field Story from Georgia
A grading contractor in Macon, Georgia experienced similar tracking loss on his 850K while working on a clay slope. The machine would move for five seconds and then stop, requiring a restart. After ruling out electrical faults, he discovered that the hydraulic fluid had absorbed moisture during winter storage, causing valve stiction. A full fluid replacement and solenoid cleaning restored performance, and he now stores the machine with desiccant breathers on the reservoir.
Conclusion
Tracking failure on the Case 850K dozer is often a complex interplay between electronic control and hydraulic response. While the symptoms may suggest mechanical failure, electrical faults and fluid contamination are frequently the root cause. With methodical diagnostics, proper calibration, and preventative maintenance, operators can restore full functionality and keep the 850K moving confidently across any terrain.