Diagnosing Drive Motor Failure on the Bobcat 553 Skid Steer

[MikePhua]

The Bobcat 553 and Its Compact Drive System
The Bobcat 553 skid steer loader was introduced in the late 1990s as part of Bobcat’s compact utility lineup. With a rated operating capacity of 950 lbs and powered by a 22-horsepower Kubota diesel engine, the 553 was designed for tight-space maneuvering, light material handling, and residential landscaping. Its hydrostatic drive system uses two independent hydraulic motors—one for each side—to control travel and steering through variable displacement.
Unlike newer electronically modulated machines, the 553 relies on mechanical linkages and pilot valves to regulate hydraulic flow. The drive motors are axial piston units mounted directly to the chain case, receiving pressurized fluid from the main pump. When one motor fails, the machine may pull to one side, lose travel power, or become completely immobile.
Symptoms of Drive Motor Problems
Operators may encounter:

• One side of the machine fails to move or moves slowly
  
• Loud whining or grinding noise from the chain case
  
• Hydraulic fluid overheating during travel
  
• Jerky or hesitant movement under load
  
• No response to steering input on one side
  
• Visible leakage near the motor housing
  

These symptoms suggest internal wear, seal failure, or contamination in the drive motor. In some cases, the issue may originate upstream in the pump or control valve, but motor failure is common in older units with high hours.
Root Causes of Motor Failure
Several factors contribute to drive motor breakdown:

• Contaminated hydraulic fluid
  Dirt, metal shavings, or water in the fluid can score motor pistons and valve plates.
  
• Seal degradation
  Age and heat cause internal seals to harden or crack, leading to pressure loss and leakage.
  
• Bearing failure
  Worn bearings allow shaft misalignment, increasing friction and reducing torque output.
  
• Overloading or aggressive operation
  Repeated high-load travel or abrupt directional changes stress the motor beyond design limits.
  
• Improper fluid viscosity
  Using incorrect hydraulic oil can reduce lubrication and accelerate wear.
  

A technician in Iowa once diagnosed a Bobcat 553 that veered left during travel. The right-side motor had a cracked valve plate and scored pistons due to water contamination. After replacing the motor and flushing the system, the machine returned to full function.
Inspection and Repair Strategy
To confirm motor failure:

• Lift the machine and test wheel rotation manually
  
• Check hydraulic pressure at the motor inlet and outlet
  
• Inspect the motor housing for cracks, leaks, or discoloration
  
• Drain and examine hydraulic fluid for debris or emulsification
  
• Remove the motor and inspect internal components for scoring or wear
  

If the motor is confirmed faulty:

• Replace with a remanufactured or new unit matched to the serial number
  
• Flush the entire hydraulic system, including filters and reservoir
  
• Inspect the opposite motor for signs of wear—failure often occurs in pairs
  
• Replace fluid with manufacturer-recommended viscosity and additive package
  
• Test system pressure and flow after installation
  

Preventive Measures and Long-Term Reliability
To extend motor life:

• Change hydraulic fluid and filters every 250 hours
  
• Use ISO 46 hydraulic oil unless operating in extreme temperatures
  
• Avoid abrupt directional changes at full throttle
  
• Keep the chain case clean and sealed
  
• Monitor fluid temperature during long travel sessions
  

Some owners install inline magnetic filters to capture metal particles before they reach the motors. Others retrofit temperature sensors to alert operators when fluid exceeds safe thresholds.
A Story from the Field
In 2023, a landscaping crew in Oregon noticed their Bobcat 553 would stall when turning right uphill. After checking the pump and control valves, they discovered the right drive motor had seized due to bearing collapse. The motor was replaced with a remanufactured unit, and the crew added a fluid sampling port to monitor contamination. The machine ran another 400 hours without issue.
Conclusion
Drive motor failure in the Bobcat 553 is a common issue as these machines age, especially when fluid maintenance is neglected. With careful diagnosis, proper replacement, and system flushing, the 553 can be restored to reliable service. In compact loaders, movement is everything. When the motors spin true and the fluid flows clean, the job moves forward with confidence.