Troubleshooting Brake Lockup in the Case 850G Dozer

[MikePhua]

The Case 850G and Its Role in Mid-Size Earthmoving
The Case 850G crawler dozer was introduced in the late 1990s as part of Case Construction Equipment’s G-series lineup, designed to serve mid-range grading, site preparation, and light clearing tasks. With an operating weight of approximately 17,000 lbs and powered by a 6-cylinder diesel engine producing around 90 horsepower, the 850G offered a balance of maneuverability and pushing power. Its hydrostatic transmission and differential steering system allowed for precise control in confined spaces, making it a popular choice among contractors and landowners.
Case, a brand under CNH Industrial, has a long legacy dating back to 1842. The 850 series has seen multiple iterations, with the G model representing a refinement in hydraulic control, operator comfort, and serviceability. Thousands of units were sold across North America, and many remain in active use today, especially in rural and owner-operated fleets.
Symptoms of Brake Lockup After Extended Downtime
One common issue reported with the 850G is brake lockup after the machine has been idle for an extended period. In a documented case, the dozer had performed reliably until it sat unused for several months. Upon restarting, one of the brakes failed to release, rendering the machine immobile.
Initial symptoms included:

• One track failing to engage while the other operated normally
  
• Brake pedal resistance or sticking
  
• No fault codes or dashboard alerts
  
• Audible clicking from solenoids but no hydraulic response
  

This behavior pointed toward a failure in the parking brake release system, which is hydraulically actuated via solenoid valves and controlled through a relay circuit.
Mechanical Linkage and Pedal Binding
Before diving into electrical diagnostics, it’s essential to inspect the mechanical linkage. The brake pedals on the 850G are mounted to the firewall and connected via rods and pivot points to the transmission control. These linkages include grease fittings, which, if neglected, can seize due to corrosion or dust accumulation.
Recommended steps:

• Apply penetrating oil to all pivot points and linkage arms
  
• Disconnect linkage from the firewall and verify free movement
  
• Grease fittings thoroughly and cycle pedals manually
  
• Inspect for bent rods or misaligned bushings
  

In many cases, pedal binding alone can prevent the brake from releasing, especially if the machine has been stored in humid or dusty conditions.
Hydraulic and Electrical Brake Release System
The 850G uses a hydraulic parking brake system controlled by a solenoid valve. When the operator disengages the brake, the solenoid energizes, allowing hydraulic fluid to flow and release the brake pack inside the transmission.
Key components include:

• Parking brake solenoid valve
  
• Relay switch and junction block
  
• Hydraulic lines and fittings
  
• Safety interlock lever
  

If the solenoid fails to energize, the brake remains engaged. In the documented case, a jumper wire was used to bypass the relay and directly power the solenoid from the battery. This successfully released the brake, confirming that the solenoid itself was functional.
Further inspection revealed that a wire had been inadvertently disconnected from the relay junction block during previous electrical repairs. Once the wire was reconnected and continuity verified, the brake system resumed normal operation.
Condensation and Corrosion in Brake Housing
Another contributing factor to brake lockup is internal corrosion within the brake housing. Over time, condensation can accumulate inside the sealed brake chamber, especially in machines stored outdoors or in unventilated sheds. This moisture leads to rust buildup, which can seize the brake discs or clog weep holes designed to drain excess fluid.
Preventive measures include:

• Drilling and cleaning weep holes if blocked
  
• Flushing brake housing with light hydraulic oil
  
• Installing desiccant breathers or moisture traps
  
• Operating the machine periodically to circulate fluid
  

In older Case machines like the 580 backhoe and 450 crawler, similar issues have been observed, reinforcing the need for regular brake housing inspection.
Steering and Brake Interaction
It’s important to note that the 850G does not use pedal steering. Instead, it relies on track speed levers to control direction. The brake pedals are primarily used for parking and emergency stops. If one brake engages unintentionally, it can cause the affected track to enter neutral, resulting in asymmetric movement or complete immobilization.
Operators should verify:

• Track speed lever function
  
• Brake adjustment settings (typically not required unless over 8,000 hours)
  
• Safety lever engagement and transmission interlock
  

In the case discussed, the machine had nearly 7,000 hours and had never required brake adjustment, suggesting that wear was not the primary issue.
Anecdote from Central Texas
A retired operator in Texas shared his experience with an 850G that had sat idle for a season. Upon startup, the left track refused to engage. After ruling out electrical faults, he discovered that a family of mice had nested inside the relay box, chewing through several wires. After cleaning the junction block and replacing damaged wires, the machine returned to full function. He now stores the dozer with mothballs and a tarp to deter rodents and moisture.
Recommendations for Long-Term Reliability
To maintain brake system integrity on the Case 850G:

• Cycle the machine monthly if stored long-term
  
• Lubricate pedal linkages and inspect for binding
  
• Test solenoid and relay circuits annually
  
• Keep electrical junction blocks clean and sealed
  
• Monitor hydraulic fluid condition and replace every 1,000 hours
  

For machines used seasonally, consider installing a battery disconnect switch and moisture-absorbing pads in the cab and relay compartments.
Conclusion
Brake lockup in the Case 850G dozer is often caused by a combination of mechanical binding, electrical disconnection, and hydraulic flow interruption. While the symptoms may seem severe, most issues can be resolved with basic diagnostics and preventive care. By understanding the interplay between pedal linkage, solenoid control, and moisture management, operators can keep their machines running smoothly—even after long periods of inactivity. The 850G remains a reliable workhorse, and with proper attention, it can continue serving for decades.