CAT 953 LGP Loss of Drive Diagnosing Hydrostatic and Mechanical Failures

[MikePhua]

The CAT 953 LGP and Its Hydrostatic System
The Caterpillar 953 LGP (Low Ground Pressure) track loader was designed for soft terrain, landfill work, and grading applications where flotation and traction are critical. Introduced in the 1980s and refined through the 1990s, the 953 series became one of CAT’s most successful crawler loaders, with thousands sold globally. The LGP variant features wider tracks and a longer undercarriage to reduce ground pressure, making it ideal for swampy or unstable surfaces.
The 953 is powered by a CAT 3204 or 3114 diesel engine, depending on the year, and uses a hydrostatic transmission system. This system allows infinite speed control and smooth directional changes without shifting gears. Drive power is transmitted through hydraulic pumps and motors rather than mechanical gearboxes, offering excellent control but requiring precise fluid management and component integrity.
Terminology Annotation:

• Hydrostatic Transmission: A drive system using hydraulic fluid to transfer power from engine to final drives via pumps and motors.
  
• Final Drive: The gear reduction assembly at each track that converts hydraulic motor output into torque.
  
• Charge Pressure: The baseline hydraulic pressure that feeds the main pumps and prevents cavitation.
  

Symptoms of Drive Loss
When a CAT 953 LGP loses drive, the symptoms may include:

• No response when engaging forward or reverse
  
• Engine revs normally but machine does not move
  
• Jerky or intermittent movement before complete failure
  
• Audible whining or cavitation noise from pump area
  
• Hydraulic fluid overheating or foaming
  

In one documented case, a 953 LGP stopped moving after a brief period of sluggish response. The engine ran smoothly, but the tracks remained stationary. The operator suspected a transmission failure, but further inspection revealed a failed charge pump seal and low fluid level.
Hydraulic System Diagnosis
To diagnose drive loss:

• Check hydraulic fluid level and condition—milky fluid indicates water contamination
  
• Inspect charge pressure at test ports—should read 300–500 PSI at idle
  
• Monitor main pump output—should exceed 5,000 PSI under load
  
• Test travel motors for internal leakage using case drain flow meters
  
• Inspect filters and screens for debris or metal particles
  

If charge pressure is low, the hydrostatic pumps may cavitate, causing loss of drive. A failed charge pump, clogged suction screen, or leaking seal can all contribute. In some cases, the pilot control system may fail to send signals to the pumps, especially if solenoids or wiring are damaged.
Mechanical and Electrical Considerations
Beyond hydraulics, mechanical failures can also cause drive loss:

• Broken drive shaft between engine and pump
  
• Stripped splines on couplings or hubs
  
• Failed planetary gears in final drives
  
• Electrical faults in travel control switches or sensors
  

Recommendations:

• Inspect drive couplings for wear or misalignment
  
• Use a stethoscope to listen for internal gear noise
  
• Test electrical continuity at travel control harness
  
• Check for fault codes if equipped with diagnostic interface
  

In one repair case from Oregon, a 953 lost drive due to a sheared key on the pump input shaft. The failure was misdiagnosed as a hydraulic issue until teardown revealed the mechanical break.
Preventative Maintenance and Fluid Strategy
To prevent drive loss:

• Change hydraulic fluid every 1,000 hours or annually
  
• Replace filters every 500 hours or sooner if contaminated
  
• Use CAT HYDO Advanced 10 or equivalent ISO 46 fluid
  
• Inspect suction screens and clean every 250 hours
  
• Monitor charge pressure monthly and log trends
  

Installing a charge pressure gauge in the cab can help detect early signs of pump wear or fluid starvation. In high-duty cycles, consider upgrading to synthetic hydraulic fluid for better thermal stability.
Parts Sourcing and Rebuild Options
Parts for the 953 LGP are widely available through:

• CAT dealers with legacy support
  
• Aftermarket suppliers specializing in hydrostatic systems
  
• Rebuild shops offering remanufactured pumps and motors
  
• Salvage yards with older CAT inventory
  

Common replacement components:

• Charge pump and seal kit
  
• Travel motor rebuild kit
  
• Hydraulic filter and screen set
  
• Drive couplings and splines
  
• Electronic travel control switches
  

In one rebuild case, a contractor replaced both travel motors and the charge pump on a 953 for under $6,000 using remanufactured parts. The machine returned to full operation and logged over 2,000 hours post-repair.
Conclusion
Loss of drive in a CAT 953 LGP is often a complex interplay of hydraulic, mechanical, and electrical factors. With methodical diagnostics, proper fluid management, and timely component replacement, the issue can be resolved without full transmission replacement. The hydrostatic system offers precision and power—but demands vigilance. In the world of tracked loaders, movement is everything—and when it stops, knowing where to look makes all the difference.