Replacing the Air Compressor on a Caterpillar 950B Loader

[MikePhua]

The 950B and Its Engine Air System
The Caterpillar 950B wheel loader, introduced in the early 1980s, was built for mid-range earthmoving, aggregate handling, and industrial loading. Powered by the CAT 3304 engine, this model became a staple in quarries and construction sites across North America and Europe. With an operating weight of approximately 35,000 pounds and a bucket capacity of 3.5 to 4.0 cubic yards, the 950B offered a balance of power and maneuverability.
One often-overlooked component in its operation is the engine-mounted air compressor. This unit supplies pressurized air for braking systems, pneumatic controls, and auxiliary functions. Over time, the compressor can degrade, leading to reduced pressure output and oil contamination in the air lines—symptoms that signal the need for replacement or rebuild.
Terminology and Component Notes
- Air Compressor: A mechanically driven pump that supplies pressurized air to the vehicle’s pneumatic systems.
- Governor: A pressure-sensitive valve that controls compressor cut-in and cut-out points, typically set around 60 psi on and 120 psi off.
- Oil Carryover: A condition where engine oil leaks into the air system, often due to worn piston rings or seals in the compressor.
- Remanufactured Unit: A used component rebuilt to OEM specifications, often with warranty coverage.
- Cross-Reference Part Number: An alternative part number used to identify compatible components across different manufacturers.
Symptoms of Compressor Failure and Initial Inspection
In one case, a 1983 CAT 950B began struggling to build rated air pressure, and excessive oil was found in the air system. The compressor lacked an identification tag, but the crankcase was stamped “Made in England” and “Clayton, Demandre,” with casting number 5F 22A75. This suggested an older single-cylinder design, possibly shared with over-the-road trucks using similar engines.
Common failure indicators include:

• Slow air pressure buildup
  
• Oil mist or pooling in air tanks and valves
  
• Increased compressor noise or vibration
  
• Inconsistent governor cycling
  
• Difficulty maintaining brake pressure under load
  

These symptoms typically point to worn internal seals, piston ring degradation, or valve plate damage.
Replacement Options and Cross-Referencing
Caterpillar no longer offers remanufactured compressors for this model, but parts for rebuilds remain available. However, many operators opt for aftermarket replacements due to cost and convenience. By cross-referencing the suspected CAT part numbers—1W6753 or 1W6755—technicians identified compatible Bendix units commonly used in highway trucks with CAT 3304 or 3306 engines.
Replacement strategies include:

• Contacting truck parts suppliers for Bendix or Bepco equivalents
  
• Using casting numbers and governor specs to match compressor types
  
• Swapping fittings and adjusting governor settings during installation
  
• Verifying mounting flange and pulley alignment before final torque
  

One operator sourced a compressor from CTP through Amazon, noting that the unit arrived on time, fit perfectly, and performed smoothly. The casting quality was solid, and no core return was required—allowing the original unit to be rebuilt later.
Installation Tips and Governor Adjustment
When installing a new compressor:

• Transfer all air and oil fittings from the old unit
  
• Clean mating surfaces and use new gaskets or O-rings
  
• Torque mounting bolts to spec to prevent vibration
  
• Adjust the governor to standard settings: 60 psi cut-in, 120 psi cut-out
  
• Test the system for leaks and monitor pressure buildup
  

If the governor is reused, inspect its diaphragm and spring for wear. A faulty governor can cause premature cycling or pressure loss, even with a new compressor.
Rebuild Considerations and Cost Analysis
Rebuilding the original compressor is viable if parts are available and the housing is intact. CAT lists most internal components, though the catalog can be confusing. Rebuild kits typically include:

• Piston rings
  
• Valve plates
  
• Gaskets and seals
  
• Bearings
  
• Governor diaphragm
  

However, with aftermarket compressors priced around $350 delivered, rebuilding may not be cost-effective unless downtime is critical or the original unit has unique mounting features.
Caterpillar’s Loader Legacy and 950B Market Impact
Caterpillar’s 950 series has been in production since the 1960s, with the 950B marking a shift toward improved cab ergonomics and hydraulic refinement. The 950B was assembled in Belgium for certain markets, and its components—especially air systems—often reflected European sourcing.
Sales of the 950B were strong throughout the 1980s, with many units still operating in quarries and municipal fleets. Its durability and parts availability have kept it viable, though some components like air compressors now require aftermarket solutions.
Conclusion
Replacing the air compressor on a CAT 950B is a straightforward task when armed with the right part numbers and sourcing strategy. Whether choosing a Bendix cross-reference, a Bepco unit, or a CTP aftermarket option, the key is ensuring compatibility and proper governor adjustment. In the world of legacy loaders, air pressure isn’t just about brakes—it’s about keeping the machine responsive, safe, and ready to work. And when the compressor finally breathes new life into the system, it’s a quiet victory that keeps the iron moving.