Bringing a Neglected John Deere 850B Dozer Back to Life

[MikePhua]

The 850B and Its Mechanical Backbone
The John Deere 850B crawler dozer was introduced in the late 1980s as part of Deere’s mid-size earthmoving lineup. With an operating weight of roughly 42,000 lbs and powered by a turbocharged 6-cylinder diesel engine, the 850B was designed for grading, pushing, and land clearing. Its hydrostatic transmission, robust undercarriage, and modular component layout made it a favorite among contractors and municipalities alike.
Despite its reputation for durability, the 850B—like any machine—can suffer from neglect. When maintenance is deferred for years, systems degrade, seals dry out, and performance drops. Reviving such a unit requires methodical inspection, mechanical empathy, and a willingness to dig deep.
Initial Assessment and Startup Strategy
When approaching a neglected 850B, begin with a non-invasive walkaround:

• Check fluid levels: engine oil, transmission fluid, hydraulic oil, coolant
  
• Inspect hoses and belts for cracking or dry rot
  
• Look for signs of rodent damage in wiring and insulation
  
• Verify battery voltage and cable integrity
  
• Examine track tension and undercarriage wear
  

Before attempting startup:

• Drain and replace all fluids to eliminate water, sludge, or contamination
  
• Install new filters across all systems
  
• Prime the fuel system and bleed air from injectors
  
• Disconnect the alternator and starter to bench test separately
  
• Use a remote starter switch to crank the engine while monitoring oil pressure
  

A contractor in Montana once revived an 850B that had sat for eight years by flushing the fuel tank, replacing the lift pump, and hand-priming the injectors. The engine fired on the third attempt and ran smoothly after a few minutes of warm-up.
Hydraulic System Rehabilitation
The 850B uses an open-center hydraulic system with gear-driven pumps and pilot-operated valves. Neglect can lead to:

• Sluggish blade response
  
• Noisy pump operation
  
• Leaking cylinder seals
  
• Contaminated fluid with metal shavings or water
  

To restore function:

• Flush the reservoir and clean the suction screen
  
• Replace all hydraulic filters and inspect return lines
  
• Test pump output pressure (should exceed 2,500 psi under load)
  
• Rebuild cylinders showing drift or external leakage
  
• Inspect valve spools for sticking or internal bypass
  

Use ISO 46 hydraulic oil or equivalent, and avoid mixing brands or viscosities. A technician in Georgia once traced slow blade lift to a collapsed suction hose hidden behind the frame—replacing it restored full speed.
Transmission and Final Drive Checks
The hydrostatic transmission in the 850B is sensitive to fluid quality and filter condition. Symptoms of neglect include:

• Jerky travel or hesitation
  
• Whining or growling noises
  
• Overheating under load
  
• Weak response in forward or reverse
  

Steps to address:

• Drain and replace transmission fluid with Hy-Gard or equivalent
  
• Replace charge pump and case drain filters
  
• Inspect drive motor couplings and splines
  
• Test charge pressure and loop pressure under load
  
• Check final drive oil levels and inspect for metal debris
  

If the machine creeps or stalls, inspect the swash plate actuator and feedback sensors. A fleet manager in Ontario once resolved a travel issue by replacing a worn servo valve that had stuck in partial displacement.
Cooling System and Engine Health
The 6-cylinder engine in the 850B is robust but vulnerable to overheating if neglected. Key areas to inspect:

• Radiator fins for clogging or bent passages
  
• Water pump for bearing noise or leaks
  
• Thermostat for proper opening temperature
  
• Fan belts and tensioners
  
• Coolant condition and freeze point
  

Flush the cooling system and replace with a 50/50 mix of ethylene glycol and distilled water. Use test strips to verify pH and corrosion inhibitors. If the engine runs hot, consider installing an auxiliary fan or upgrading the radiator core.
Electrical System and Instrumentation
Neglected machines often suffer from electrical gremlins:

• Dead gauges or warning lights
  
• Starter solenoid failure
  
• Alternator not charging
  
• Corroded connectors or broken wires
  

To restore reliability:

• Replace the battery with a high-CCA unit
  
• Clean all ground points and apply dielectric grease
  
• Inspect fuse block and relays for corrosion
  
• Test alternator output and regulator function
  
• Rewire damaged circuits using marine-grade wire and sealed connectors
  

A dozer in Texas had no dash function until the crew discovered a chewed-through ground wire under the cab. Repairing the wire restored all gauges and warning systems.
Undercarriage and Structural Integrity
The undercarriage is the foundation of any crawler. On the 850B, inspect:

• Track tension and alignment
  
• Roller and idler wear
  
• Sprocket teeth for hooking or chipping
  
• Frame welds and blade mounts for cracks
  
• Pivot pins and bushings for play
  

Grease all fittings and replace missing seals. If the tracks are loose, adjust via the grease cylinder behind the idler. A forestry crew in Oregon once rebuilt their 850B’s track adjusters using aftermarket seals and restored proper tension after years of slop.
A Story from the Field
In 2021, a landowner in Pennsylvania acquired a neglected 850B from a county auction. The machine had sat for six years, covered in leaves and rust. Over two months, he replaced fluids, rebuilt the starter, flushed the hydraulics, and rewired the dash. The dozer returned to service clearing trails and grading driveways. Locals dubbed it “The Green Ghost,” and it became a symbol of practical restoration.
Conclusion
Reviving a neglected John Deere 850B is a rewarding challenge that blends mechanical skill with diagnostic patience. By addressing hydraulics, transmission, cooling, and electrical systems methodically, operators can restore full functionality and extend the life of this iconic machine. In the world of legacy iron, the 850B remains a workhorse worth saving—one seal, one wire, one bolt at a time.