John Deere 850B Dozer: Performance, Pitfalls, and Practical Wisdom

[MikePhua]

Overview of the 850B Series
The John Deere 850B crawler dozer, produced from the mid-1980s to mid-1990s, was designed for mid-size earthmoving tasks. It featured a hydrostatic transmission, a turbocharged 6-cylinder diesel engine, and a robust undercarriage suited for both standard and low ground pressure (LGP) configurations. While praised for its pushing power and operator comfort, the 850B also earned a reputation for complex maintenance and transmission quirks.
Terminology Notes

• Hydrostatic Transmission: A drive system using hydraulic fluid to transmit power, allowing smooth variable speed control without gear shifting.
  
• Pedal Steer: Steering via foot pedals rather than hand levers, common in hydrostatic machines.
  
• EROPS: Enclosed Roll-Over Protective Structure, providing operator safety and climate control.
  
• LGP Configuration: Low Ground Pressure setup with wider tracks for better flotation on soft terrain.
  
• Sundstrand Pumps: Hydraulic pumps used in the transmission system, known for precision but costly to replace.
  

Performance Highlights

• Strong pushing capability in soft or marshy conditions
  
• Smooth directional control with hydrostatic drive
  
• Comfortable cab layout with good visibility
  
• Effective in slope work and cell finishing tasks
  
• Nimble handling for mid-size clearing and grading
  

Common Issues and Maintenance Challenges

• Hydrostatic Syncing: Keeping both sides of the drive system balanced can be difficult, especially after repairs.
  
• Pump Replacement Costs: Sundstrand hydraulic pumps are expensive and often unsupported by manufacturers.
  
• Radiator Vulnerability: Poor screen design can allow debris to puncture the radiator.
  
• Reverse Speed Lag: Some units exhibit sluggish reverse movement, with limited dealer support for resolution.
  
• Track Cleaning Difficulty: The undercarriage design traps mud and vegetation, requiring extensive manual cleaning.
  

Field Anecdotes and Operator Insights
One operator recalled working in a cattail marsh where the tracks packed with peat and stems so tightly that the last hour of each day was spent on hands and knees clearing the undercarriage. Another shared a story of losing forward control due to a failing hydraulic pump, forcing them to back the machine home and rebuild the pump themselves—saving over $20,000 compared to a factory replacement.
A mechanic noted that when the hydrostatic system fails, it often contaminates the entire hydraulic circuit. Without thorough purging of lines, filters, and valves, rebuilt components can quickly fail again. In one case, a rebuilt pump lasted only weeks due to residual debris in the system.
Preventive Measures and Best Practices

• Regularly inspect and clean track assemblies, especially in wet environments
  
• Monitor hydraulic fluid quality and change filters frequently
  
• Avoid overloading the transmission in cold weather
  
• Install protective screens to shield the radiator from debris
  
• Document serial numbers and component specs for easier parts sourcing
  

Design Evolution and Historical Context
The 850B followed the original 850 and preceded the 850C, each iteration improving on cab ergonomics, hydraulic efficiency, and serviceability. While the B model introduced hydrostatic drive for smoother control, it also brought complexity that challenged field mechanics. Later models addressed many of these concerns with better diagnostics and modular components.
Conclusion: A Capable Machine with Caveats
The John Deere 850B is a solid performer when properly maintained, especially in soft terrain and precision grading. However, its hydrostatic system demands respect and careful upkeep. For operators willing to invest time in learning its quirks and maintaining its systems, the 850B can be a reliable workhorse. As one veteran put it, “When it’s right, it’s a joy to run. When it’s wrong, it’ll test your patience—and your wallet.”