Troubleshooting and Rebuilding Drive Motors on the Bobcat 753

[MikePhua]

Understanding the Bobcat 753 Drive System
The Bobcat 753 skid steer loader, popular for its durability and ease of service, uses a hydrostatic drive system composed of two variable-displacement hydraulic pumps (one for each side) that power fixed-displacement drive motors. These motors are directly connected to planetary final drives which transfer torque to the wheels. The hydrostatic system allows for smooth, infinitely variable speed control and counter-rotation steering, making it highly maneuverable in tight spaces.
Drive motors on this machine are piston-type hydraulic motors, designed to operate under high pressure. Over time, these components can fail due to contamination, bearing wear, cavitation, heat damage, or misalignment. Understanding the symptoms and failure points is key to cost-effective repair and long-term reliability.
Common Symptoms of Drive Motor Issues

• Loss of power on one side
  
• Sluggish movement when the loader is cold or under load
  
• Unusual whining or growling noises from the drive motor area
  
• Hydraulic fluid foaming or overheating
  
• Machine veering to one side during operation
  
• Complete failure to move despite engine running normally
  

A sudden or gradual failure in one motor can mimic steering or control problems. It's critical to isolate the fault before assuming pump failure.
Diagnosing the Problem: Process of Elimination
Before removing a motor, it's important to perform a series of systematic checks:

• Check hydraulic fluid level and condition: Low or contaminated fluid can mimic motor failure
  
• Swap hydraulic hoses between motors: If the problem switches sides, it’s pump-related
  
• Check case drain flow: Excessive case drain can indicate internal leakage in the motor
  
• Listen for noise changes under load: A grinding or knocking sound is often a bearing or shaft issue
  
• Examine wheel hub rotation: Binding could indicate brake or final drive problems, not motor failure
  

Case Drain Testing: The Key to Confirmation
A common diagnostic technique involves measuring case drain flow—the amount of oil leaking past internal motor components. Excessive flow indicates wear or internal bypassing.
Normal case drain flow for a healthy motor is minimal. If a drive motor flows more than 2 gallons per minute from the case drain line, it is likely suffering from:

• Worn piston shoes
  
• Cracked valve plate
  
• Damaged cylinder block
  
• Leaking shaft seal or bearings
  

One technician reported seeing a steady stream from the case drain of the right motor while the left remained almost dry—an unmistakable sign of failure on the right side.
Disassembling the Drive Motor: Tips and Warnings
Drive motor removal on the 753 involves more than just disconnecting hoses. Safety and cleanliness are crucial.
Steps for removal:

• Park the loader on a clean, level surface and lower the arms
  
• Disconnect battery to prevent unintended hydraulic actuation
  
• Remove wheel and access the motor through the side panels
  
• Cap all hydraulic lines to prevent contamination
  
• Drain hydraulic fluid from the reservoir
  
• Use lifting equipment if needed—the motor is heavy and awkward
  
• Mark hoses for correct reinstallation
  

Important caution: Always wear eye protection when working with pressurized hydraulic lines. Residual pressure can cause oil jets that result in injury.
Inside the Drive Motor: Key Components and Wear Points
A typical Bobcat 753 drive motor includes:

• Cylinder block with piston bores
  
• Swashplate which varies the stroke of pistons
  
• Valve plate with pressure ports
  
• Shaft with splines that connect to final drive
  
• Thrust and radial bearings
  
• Case housing that holds it all together
  

The most common failure modes include:

• Scoring or pitting on the valve plate
  
• Worn or cracked piston shoes
  
• Galling on the cylinder block face
  
• Bearing collapse leading to shaft misalignment
  
• Shaft seal leaks causing external oil loss
  

Repair vs Replacement: Making the Right Call
Once disassembled, the next step is to evaluate whether the motor can be rebuilt or must be replaced.
When to rebuild:

• Cylinder block and valve plate are still usable
  
• No cracking or warping on housing
  
• Bearings can be replaced with OEM-equivalent parts
  
• No shaft scoring that exceeds spec
  

When to replace:

• Housing is cracked
  
• Piston bores are egg-shaped
  
• Parts availability is limited or cost-prohibitive
  
• Excessive heat damage has altered metal hardness
  

Some users have successfully rebuilt their motors for under $700 in parts, while replacement motors can cost upwards of $2,500. Labor time varies but typically takes 4 to 8 hours for a full teardown and rebuild, assuming all parts are on hand.
Real-World Story: A Bobcat That Pulled Left
A farm operator in Minnesota noticed his Bobcat 753 consistently pulled left during forward movement. Thinking it was a tire pressure issue, he first swapped wheels—but the problem persisted. Case drain testing revealed that the right-side motor was leaking significantly. After sourcing a rebuild kit and enlisting a mobile mechanic, the motor was rebuilt on-site. Total cost: under $900. The loader now tracks straight and responds better to joystick input.
Reassembly and Precautionary Measures
Before reassembly:

• Clean all parts in solvent
  
• Replace all seals, O-rings, and gaskets
  
• Check swashplate surface finish
  
• Use assembly lube or clean hydraulic oil for piston and shoe installation
  
• Torque all fasteners to spec
  
• Prime the system with clean hydraulic fluid before startup
  

Post-repair checks:

• Bleed air from lines
  
• Monitor case drain during break-in
  
• Listen for abnormal noises
  
• Check for leaks at hose fittings and shaft seals
  
• Retorque bolts after 10 hours of operation
  

Preventive Maintenance to Extend Drive Motor Life

• Change hydraulic filters every 250 hours
  
• Use only clean, manufacturer-approved hydraulic fluid
  
• Keep case drain lines free of restriction
  
• Inspect for water ingress or foaming in oil
  
• Don’t idle the machine with drive pressure for long periods
  
• Grease wheel hubs and check for abnormal resistance
  

Conclusion: Repairable and Reliable With the Right Know-How
The Bobcat 753 remains one of the most reliable skid steers of its era, and its hydrostatic drive system—while complex—is fully serviceable with the right tools and understanding. Whether you're a seasoned technician or a dedicated owner-operator, recognizing the symptoms of drive motor issues early can save thousands in repairs and prevent catastrophic damage to the hydraulic system.
Armed with a pressure gauge, clean workspace, and patience, you can turn a non-functioning drive motor into a fully restored component—keeping your loader digging, lifting, and earning.