Case 855D Loader Hydraulic Control Valve Challenges and Solutions

[MikePhua]

The Case 855D and Its Role in Mid-Size Earthmoving
Case Construction Equipment, a division of CNH Industrial, has been producing wheel loaders since the 1950s. The 855D, introduced in the late 1980s, was part of Case’s D-series lineup, designed to offer high breakout force, reliable hydraulics, and simplified serviceability for contractors and municipalities. With an operating weight around 28,000 lbs and a bucket capacity of 3.5 cubic yards, the 855D was widely used for roadwork, aggregate handling, and site preparation.
Its hydraulic system was built around a gear-type pump and a multi-section control valve assembly, responsible for directing fluid to the lift, tilt, and auxiliary circuits. While robust in design, the control valve has become a focal point for maintenance and troubleshooting as these machines age.
Terminology Notes

• Control valve: A hydraulic component that regulates flow direction and volume to actuators like lift cylinders and tilt rams.
  
• Spool valve: A sliding cylindrical element inside the control valve that opens and closes fluid passages.
  
• Load check valve: Prevents hydraulic fluid from reversing direction under load, maintaining cylinder position.
  
• Float function: Allows the bucket to follow ground contours without hydraulic resistance, useful in grading.
  

Common Symptoms of Valve Malfunction
Operators of aging 855D loaders often report issues such as:

• Bucket or lift arms drifting down when parked
  
• Jerky or delayed response during lift or tilt
  
• Inability to hold load position under pressure
  
• Hydraulic fluid bypassing internally, causing overheating
  
• Float function failing to engage or disengage properly
  

These symptoms typically point to internal leakage, worn spool lands, damaged seals, or contamination within the valve body.
Root Causes and Diagnostic Strategies
The control valve on the 855D is a multi-section assembly, with each section dedicated to a specific function. Over time, the following issues may arise:

• Spool wear due to lack of lubrication or contaminated fluid
  
• O-ring and seal degradation from heat and age
  
• Scoring inside the valve bore from metal particles
  
• Weak load check springs or stuck poppets
  
• Misadjusted linkage or detent mechanisms
  

To diagnose valve issues:

• Perform a pressure test at each circuit port under load
  
• Check for external leakage around valve body and fittings
  
• Inspect spool movement for binding or excessive play
  
• Use infrared thermography to detect hotspots from internal bypass
  
• Disassemble and inspect valve sections for scoring and seal condition
  

A Story from the Midwest
In 2010, a county road crew in Iowa noticed their Case 855D loader was struggling to hold the bucket in position during snow loading. The arms would slowly drop even with the engine off. After ruling out cylinder seal failure, they pulled the control valve and found the lift spool had worn lands and a cracked load check seat. A rebuilt valve section and fresh seals restored full function. The crew noted that “the loader felt like it gained ten years of life overnight.”
Repair and Replacement Options
Depending on the severity of wear, operators have several options:

• Rebuild individual valve sections using OEM or aftermarket kits
  
• Replace entire valve assembly with remanufactured unit
  
• Upgrade to newer-style valves with improved sealing and float control
  
• Retrofit auxiliary hydraulic lines with external flow control valves
  

When rebuilding:

• Use Viton or polyurethane seals for better heat resistance
  
• Hone valve bores to remove scoring before reassembly
  
• Replace detent balls and springs to restore float and hold functions
  
• Flush hydraulic system thoroughly to prevent recontamination
  

Preventive Maintenance Recommendations
To extend the life of the control valve:

• Change hydraulic fluid every 1,000 hours or annually
  
• Replace filters every 250–500 hours depending on duty cycle
  
• Inspect linkage and spool movement monthly
  
• Grease control linkages and pivot points regularly
  
• Monitor system pressure and temperature during operation
  

Adding magnetic suction strainers and bypass filtration can reduce particulate load and extend valve life.
Parts Availability and Restoration Tips
While Case no longer produces the 855D, parts remain available through CNH dealers and aftermarket suppliers. Key components like spools, seals, springs, and valve bodies can be sourced or rebuilt.
Restoration tips:

• Label hydraulic lines before disassembly to avoid cross-connection
  
• Use torque specs from factory service manuals during reassembly
  
• Pressure test rebuilt valve before installation
  
• Upgrade to modern quick-connect fittings for easier service
  

Some owners have retrofitted newer control valves from Case 721 or 821 models, though this requires custom brackets and hose routing.
Final Thoughts
The hydraulic control valve on the Case 855D is a critical component that directly affects loader performance, safety, and operator confidence. While wear is inevitable, proper diagnosis and thoughtful repair can restore full functionality and extend the machine’s working life. In a loader built for hard work, the control valve is the brain behind the muscle—and keeping it healthy ensures the rest of the system follows suit.