Maintaining Fluids and Filters on the Caterpillar 955L Track Loader

[MikePhua]

The 955L and Its Mechanical Legacy
The Caterpillar 955L track loader is a mid-size crawler machine designed for excavation, loading, and site preparation. Introduced in the 1970s as part of Caterpillar’s evolution from cable-operated loaders to fully hydraulic systems, the 955L became a staple in construction and quarry operations. With an operating weight of approximately 15 metric tons and a bucket capacity of 2.5 cubic yards, the 955L offered a balance of power and maneuverability that made it popular across North America, Europe, and Asia.
Caterpillar, founded in 1925, has produced millions of machines globally. The 955L was powered by the Cat 3304 diesel engine, a four-cylinder workhorse known for its durability and ease of service. Though no longer in production, thousands of units remain in operation, especially in owner-operator fleets and rural job sites.
Fluid Systems and Their Importance
The 955L relies on multiple fluid systems to operate efficiently:

• Engine oil for lubrication and cooling
  
• Hydraulic fluid for bucket, lift, and tilt functions
  
• Transmission fluid for power transfer and gear shifting
  
• Final drive oil for track propulsion
  
• Coolant for engine temperature regulation
  

Each system has its own filter and service interval. Neglecting fluid maintenance can lead to overheating, sluggish response, or catastrophic failure. For example, contaminated hydraulic fluid can damage pump seals and valve spools, while old transmission oil can cause gear slippage and clutch wear.
Terminology Notes

• Final Drive: The gear assembly that transfers power from the transmission to the tracks
  
• Hydraulic Reservoir: The tank that stores hydraulic fluid for the system
  
• Spin-On Filter: A replaceable filter cartridge that screws directly onto a housing
  
• Bypass Valve: A safety feature that allows fluid to bypass a clogged filter
  
• Viscosity Index: A measure of how fluid thickness changes with temperature
  

Recommended Fluids and Capacities
While exact specifications vary slightly by serial number, typical fluid recommendations for the 955L include:

• Engine oil: SAE 15W-40, capacity ~4 gallons
  
• Hydraulic fluid: ISO 68 or Caterpillar HYDO Advanced 10, capacity ~30 gallons
  
• Transmission oil: SAE 30 or TO-4 fluid, capacity ~5 gallons
  
• Final drive oil: SAE 90 gear oil, ~1 gallon per side
  
• Coolant: 50/50 ethylene glycol mix, capacity ~6 gallons
  

Always consult the machine’s service manual or a dealer database to confirm fluid types and quantities. Using incorrect viscosity or additive packages can reduce component life.
Filter Types and Service Intervals
The 955L uses several filters:

• Engine oil filter: spin-on type, replace every 250 hours
  
• Hydraulic filter: cartridge or spin-on, replace every 500 hours
  
• Transmission filter: internal screen and external filter, inspect every 500 hours
  
• Fuel filter: primary and secondary, replace every 250 hours
  
• Air filter: dry element, inspect weekly and replace as needed
  

A contractor in Texas shared that after switching to high-efficiency hydraulic filters and synthetic fluid, his 955L ran 1,200 hours without a single valve issue, even in dusty conditions.
Common Issues and Field Solutions
Operators often encounter:

• Hydraulic hesitation due to clogged filters or low fluid
  
• Transmission slipping from degraded oil or worn clutch packs
  
• Engine overheating from low coolant or dirty radiator fins
  
• Fuel starvation from clogged filters or air in the lines
  

To resolve these:

• Bleed hydraulic lines after filter changes
  
• Use infrared thermometers to monitor fluid temperatures
  
• Install magnetic drain plugs to catch metal particles
  
• Replace fuel filters in pairs to maintain flow balance
  
• Flush coolant system every 1,000 hours to remove scale
  

One technician in Alberta discovered that his loader’s sluggish lift was caused by a collapsed hydraulic filter element. Replacing it restored full function instantly.
Preventive Maintenance Recommendations
To extend machine life:

• Keep a fluid change log with hours and types used
  
• Store fluids in sealed containers away from moisture
  
• Use OEM or high-quality aftermarket filters with verified micron ratings
  
• Inspect hoses and fittings monthly for leaks or abrasion
  
• Sample hydraulic and transmission oil annually for contamination
  

For machines operating in cold climates, consider using multi-grade oils and installing block heaters to reduce startup wear.
Conclusion
The Caterpillar 955L remains a reliable workhorse when properly maintained. Fluids and filters are the lifeblood of its systems, and neglecting them can lead to costly repairs. By following structured service intervals, using correct specifications, and applying field-tested solutions, operators can keep their 955L running strong across decades of demanding work.