Adding a Third Hydraulic Valve to the Caterpillar 977L Track Loader

[MikePhua]

The 977L and Its Hydraulic Control Legacy
The Caterpillar 977L track loader was introduced in the mid-1970s as part of Cat’s evolution in crawler loaders, combining the ruggedness of dozers with the versatility of front-end loaders. With an operating weight of approximately 50,000 lbs and powered by the reliable Cat D333 turbocharged diesel engine, the 977L was widely used in quarrying, demolition, and heavy construction. Its hydraulic system was designed around simplicity and durability, typically featuring two control valves—one for lift and one for tilt.
As jobsite demands evolved, many operators sought to expand the machine’s functionality by adding a third hydraulic valve. This modification allows the use of auxiliary attachments such as rippers, clamshell buckets, or custom implements, transforming the 977L into a more adaptable tool carrier.
Terminology Clarification

• Hydraulic control valve: A directional valve that regulates the flow of hydraulic fluid to actuators like cylinders or motors.
  
• Spool: The internal sliding component of a valve that opens and closes fluid paths.
  
• Stacked valve bank: A modular arrangement of multiple valves bolted together, sharing a common pressure and return manifold.
  
• Pilot control: A low-pressure hydraulic signal used to actuate larger valves.
  

Planning the Third Valve Integration
Before adding a third valve, several factors must be considered:

• Compatibility with existing valve bank and hydraulic pump output
  
• Space constraints within the loader’s control compartment
  
• Routing of new hoses and lines to the target attachment
  
• Control lever placement and operator ergonomics
  
• Pressure and flow requirements of the new circuit
  

A technician in Alberta retrofitted a 977L with a third valve to operate a rear-mounted ripper. He sourced a matching valve section from a salvage yard and fabricated custom brackets to mount the new control lever beside the existing lift and tilt handles.
Installation Procedure and Component Selection
To install a third valve:

• Identify the valve model and manufacturer used in the original bank (often Vickers or Caterpillar-branded)
  
• Source a compatible third section with matching spool configuration
  
• Disassemble the valve bank and insert the new section, ensuring proper gasket and seal alignment
  
• Connect pressure, return, and load-sensing lines using high-pressure rated hose
  
• Install a new control lever or pilot joystick in the operator station
  
• Route hydraulic lines to the attachment point, securing with clamps and guards
  

Recommended components:

• SAE-rated hydraulic hose with crimped fittings
  
• Steel mounting brackets for lever support
  
• Inline filters to protect new circuit from contamination
  
• Pressure relief valve if the attachment has lower pressure tolerance
  

A contractor in Georgia added a third valve to his 977L to operate a clamshell bucket. He used a diverter valve to split flow between the tilt and auxiliary functions, allowing control without modifying the original valve bank.
Testing and Calibration
After installation:

• Fill the hydraulic reservoir and bleed air from the new lines
  
• Start the engine and cycle the new valve slowly to check for leaks
  
• Monitor system pressure with a gauge during operation
  
• Adjust relief valve settings to match attachment specifications
  
• Test full range of motion and verify control responsiveness
  

Safety tips:

• Wear eye protection and gloves when working with pressurized fluid
  
• Use torque specs from the valve manufacturer for all fasteners
  
• Avoid routing hoses near hot exhaust components
  
• Label new controls clearly to prevent operator confusion
  

A fleet manager in British Columbia added color-coded decals to his modified 977L controls, reducing training time for new operators and preventing misoperation during multi-function tasks.
Maintenance and Long-Term Reliability
To ensure the third valve performs reliably:

• Inspect hoses and fittings monthly for wear or leaks
  
• Replace hydraulic filters every 500 hours or after major service
  
• Grease control linkages and pivot points quarterly
  
• Monitor fluid temperature during extended use of auxiliary attachments
  
• Keep valve spools clean and free of debris
  

Operator tips:

• Avoid holding the valve in relief position for extended periods
  
• Use float mode when possible to reduce pressure buildup
  
• Report sluggish response or unusual noises immediately
  
• Store attachments with cylinders retracted to protect seals
  

A crew in Texas added a third valve to their 977L fleet and implemented a preventive checklist. Over two years, they saw a 30% increase in attachment utilization and reduced downtime from hydraulic failures.
Conclusion
Adding a third hydraulic valve to the Caterpillar 977L is a practical upgrade that unlocks new capabilities for a proven workhorse. With careful planning, compatible components, and disciplined installation, operators can expand the machine’s versatility without compromising reliability. Whether powering a ripper, grapple, or custom tool, the third valve transforms the 977L from a loader into a multi-role platform ready for modern jobsite demands. In heavy equipment, adaptability is often the key to longevity.