Troubleshooting and Rebuilding Drive Motors on the Bobcat 864: Hydraulic Wear and Remanufacturing Realities

[MikePhua]

Introduction
The Bobcat 864 compact track loader is a rugged machine designed for demanding excavation and material handling tasks. Its hydraulic track drive motors are central to mobility and performance, but as these components age, leaks, pressure loss, and internal wear can lead to costly failures. This article explores the technical challenges of diagnosing and rebuilding drive motors on the Bobcat 864, clarifies key terminology, and shares field-tested insights from operators and service technicians.
Understanding the Hydraulic Drive Motor System
Each track on the Bobcat 864 is powered by a hydraulic motor fed by the main pump. These motors convert hydraulic pressure into rotational force, driving the sprockets and tracks. The system includes:

• Hydraulic drive motors (one per track)
  
• Sprocket hub and bearing assembly
  
• Charge pump and filters
  
• Hydraulic cooler
  
• Control valves and pressure relief circuits
  

Terminology Clarified

• Drive Motor: A hydraulic motor that powers the track system by converting fluid pressure into mechanical rotation.
  
• Charge Pressure: The baseline hydraulic pressure used to feed the system and maintain lubrication; low charge pressure can indicate pump or motor wear.
  
• Slippers and Valve Plates: Internal components of hydraulic pumps and motors that regulate fluid flow and pressure; wear on these parts reduces efficiency.
  
• Reman Unit: A remanufactured component rebuilt to factory specifications, often with new seals, bearings, and machined surfaces.
  

Common Symptoms and Diagnostic Path

• Hydraulic Fluid Leaking from Sprocket Hub
  Indicates seal failure or housing damage. If the outer housing is leaking, replacement may be possible without full motor rebuild, but disassembly is required.
  
• Low Charge Pressure and Repeated Failures
  Suggests internal wear in pumps or motors. Slippers and valve plates may be worn beyond service limits, especially in auctioned machines with unknown service history.
  
• Reman Motors and Pumps Failing Prematurely
  Points to poor rebuild quality or contamination. Some reman units may look new but contain reused components with excessive wear.
  

Field Anecdote: Missouri Contractor’s Cost Dilemma
A contractor in Missouri faced a leaking drive motor on his Bobcat 864. The dealer quoted $4,100 for a new unit and claimed reman options were unavailable. Frustrated, he explored third-party suppliers and considered rebuilding the motor himself. He discovered that while the outer housing could be replaced, the process required full disassembly, a seal kit, and possibly a new sprocket due to design changes. The experience highlighted the tension between OEM pricing and independent repair.
Historical Perspective: The Rise and Risk of Remanufacturing
In the early 2000s, remanufactured hydraulic components became popular as cost-saving alternatives. However, inconsistent quality control led to skepticism among dealers and technicians. Machines purchased at auction often came with reman motors and pumps that failed within weeks due to worn internal parts or improper flushing. This led some service managers to recommend full replacement over reman options, despite the higher cost.
Case Study: T300 with Dual Reman Failures
A Bobcat T300 entered a service shop with low charge pressure. It had recently received reman pumps and motors from another dealer. After flushing the system and replacing the charge pump, the issue returned. Upon inspection, the slippers and valve plates showed extreme wear—suggesting the reman units had not been properly rebuilt. The shop replaced all hydraulic components, flushed the system again, and installed new filters and a cooler. The machine returned to service with restored performance.
Best Practices for Drive Motor Repair

• Inspect the outer housing for cracks or seal damage before disassembly
  
• Use OEM or high-quality aftermarket seal kits for rebuilds
  
• Replace the sprocket if design changes affect fitment
  
• Flush the hydraulic system thoroughly before installing new or reman components
  
• Monitor charge pressure after installation to verify system health
  

Recommended Tools and Techniques

• Hydraulic pressure gauge for charge pressure testing
  
• Seal puller and bearing press for motor disassembly
  
• Torque wrench for sprocket and housing bolts
  
• Ultrasonic cleaner for internal motor components
  
• Service manual with exploded diagrams and torque specs
  

Conclusion
Repairing or replacing drive motors on the Bobcat 864 requires a balance of mechanical skill, diagnostic precision, and financial judgment. While remanufactured units offer potential savings, quality varies widely, and poor rebuilds can lead to cascading failures. By understanding the system architecture and applying rigorous inspection and flushing protocols, operators can restore performance and avoid costly downtime. In hydraulic systems, what’s hidden inside matters most—and every seal tells a story.