Caterpillar 963 Track Loader Drive Motor Failure and System Contamination Risks

[MikePhua]

Quick answer
A failed left-side drive motor on a Caterpillar 963 track loader may cost over $8,000 USD to rebuild, but the greater risk lies in system-wide contamination. If metal debris from the motor enters the hydraulic loop, the final cost could double due to pump damage and flushing requirements.
Caterpillar 963 background and hydrostatic drive system
The Caterpillar 963 track loader was introduced in the 1980s as a mid-sized crawler loader designed for grading, excavation, and material handling. It features:

• A hydrostatic transmission with dual drive motors
  
• Closed-loop hydraulic system with high-pressure charge unit (HPCU)
  
• Swash plate-controlled variable displacement motors
  
• Case drain filtration and loop flushing circuits
  

The hydrostatic system allows precise control of each track independently, enabling smooth turns and responsive operation. Drive motors are critical components, converting hydraulic energy into mechanical torque.
Failure symptoms and diagnostic clues
In one case, the left drive motor failed during routine operation. The machine had approximately 2,400–3,000 hours and had recently been used for leveling dirt piles. Initial signs included:

• Loss of left turn capability under load
  
• Motor bypassing fluid into the oil tank during pressure tests
  
• Filter inspection revealed minor metal particles
  
• Oil tank appeared clean, suggesting localized failure
  

The technician noted that the motor worked intermittently before failing completely. At idle, it could still turn slightly, but required external assistance to load onto a trailer.
Understanding motor failure and contamination pathways
Drive motor failure can occur in several ways:

• Swash plate and slipper wear: Causes internal leakage and loss of displacement control
  
• Barrel face and port plate damage: Indicates metal has entered the hydraulic loop
  
• Shaft fracture: Clean breaks may limit debris spread but still risk contamination
  

If the failure is limited to the slipper end, flushing the sump and cleaning case drain screens may suffice. However, damage to the barrel or port plate means metal has likely reached the pump, requiring full system overhaul.
Rebuild cost and sourcing advice
CAT dealers quoted $8,000 USD for motor rebuild alone. Additional costs include:

• HPCU inspection and possible rebuild
  
• Loop flushing and oil replacement
  
• Filter replacement and screen cleaning
  
• Labor for disassembly and reinstallation
  

Alternative sourcing options:

• Aftermarket rebuilders: May offer lower prices but require caution—some vendors have poor reputations
  
• Salvage yards: Used motors may be available but carry unknown wear
  
• OEM remanufactured units: Offer warranty but at premium cost
  

One technician warned against using Hydrostatic Transmission Service of Tupelo, MS due to past issues. Always verify vendor reputation before committing.
Recommended repair strategy

• Remove failed motor and inspect shaft, barrel, and port plate
  
• Flush hydraulic loop using CAT-approved filtration system
  
• Replace oil and filters, then run briefly and recheck
  
• Cut open filter to inspect for residual metal
  
• Monitor case drain flow and pressure after reinstallation
  

If the shaft broke cleanly and no debris entered the loop, a rebuild may be sufficient. However, any sign of contamination warrants full system inspection.
Conclusion
A failed drive motor on a Caterpillar 963 is more than a $8,000 repair—it’s a potential system-wide hazard. Metal contamination can damage pumps, valves, and other motors. With careful inspection, flushing, and sourcing, the loader can be restored without risking repeat failure. Proceed with caution, and prioritize system integrity over short-term savings.