Bobcat 773 Weak Lift Performance: Diagnosing Hydraulic Power Loss

[MikePhua]

Introduction: When Strength Fades in a Trusted Skid Steer
The Bobcat 773 skid steer loader is known for its compact power and versatility across construction, landscaping, and agricultural tasks. But when its lift and tilt functions become sluggish or weak—especially under load—it signals a deeper issue within the hydraulic system. This article explores the mechanical, hydraulic, and operational factors that contribute to weak lift performance, offering a structured diagnostic approach enriched with field anecdotes and historical context.
Key Terminology

• Hydraulic Gear Pump: A pump that generates flow and pressure for hydraulic functions like lift and tilt.
  
• Relief Valve: A safety valve that limits maximum hydraulic pressure to prevent system damage.
  
• Case Drain Filter: A filter that captures return flow from hydraulic components, protecting the reservoir from contamination.
  
• Auxiliary Hydraulics: Additional hydraulic circuits used to power attachments like grapples or augers.
  
• Drive Belt: A belt that transfers power from the engine to the hydraulic pump.
  

Initial Symptoms and Operator Observations
Operators often report that the Bobcat 773 drives well, climbs hills with ease, and responds quickly when empty. However, when pushing into a pile or lifting a loaded bucket, the hydraulics slow dramatically or stall. In some cases, lift and tilt functions work better when used individually, but still lack expected force. These symptoms suggest a pressure-related issue rather than a flow deficiency.
Common Causes of Weak Lift Performance

1. Worn Hydraulic Pump
   • A gear pump with worn internal surfaces may produce adequate flow but insufficient pressure under load.
     
   • Symptoms include slow lift speed, inability to hold a load, and reduced responsiveness.
     
2. Relief Valve Malfunction
   • A stuck or misadjusted relief valve may prematurely divert pressure back to the tank.
     
   • If the red relief valve near the operator seat shows no response, it may be seized or bypassing pressure.
     
3. Drive Belt Wear
   • A worn or loose belt may reduce pump RPM, especially under load.
     
   • Even without squealing, belt slippage can cause intermittent power loss.
     
4. Hydraulic Fluid and Filter Issues
   • Old or contaminated fluid reduces system efficiency.
     
   • A clogged hydro filter or neglected case drain filter can restrict flow and cause cavitation.
     
5. Air Entrapment or Cavitation
   • Air bubbles in the hydraulic fluid reduce pressure and damage pump components.
     
   • May occur after fluid changes or hose replacements without proper bleeding.
     
6. Internal Cylinder Leakage
   

• Lift cylinders with worn seals may bypass fluid internally, reducing lifting force.
  
• A cylinder leak-by test can confirm this condition.
  

Field Anecdote: The Minnesota Loader That Wouldn’t Lift
A 2003 Bobcat 773 in Minnesota showed strong drive power but weak lift and tilt. After a full fluid and filter change, the issue persisted. The operator noticed no reaction from the relief valve and suspected a pressure problem. Without a pressure gauge, diagnostics stalled. Eventually, a technician discovered the drive belt was worn and slipping under load—despite no audible squeal. Replacing the belt restored full hydraulic strength.
Historical Perspective: Evolution of Skid Steer Hydraulics
The Bobcat 773 emerged during a transition period in skid steer design, where hydraulic systems became more complex to support advanced attachments. Earlier models relied on simple open-center systems, while newer units introduced load-sensing hydraulics and electronic controls. The 773 retained mechanical simplicity but required precise maintenance to perform reliably under load.
Case Study: Pressure Testing Without a Diagnostic Port
In one case, a technician lacked access to a dedicated pressure port. Instead, they removed an auxiliary hydraulic line and installed a pressure gauge. At idle, the system barely reached 1,500 PSI—far below the expected 2,800–3,500 PSI. This confirmed a pump or relief valve issue. Replacing the pump restored full function, validating the test method.
Best Practices for Diagnosis and Maintenance

• Install a Pressure Gauge: Use auxiliary couplings or control valve ports to measure system pressure.
  
• Inspect Belt Tension and Condition: Replace worn belts even if they appear intact.
  
• Replace Filters Regularly: Include case drain filters in scheduled maintenance.
  
• Bleed Air After Fluid Changes: Run the machine through full hydraulic cycles to purge trapped air.
  
• Test Cylinders for Internal Leaks: Use a lift cylinder bypass test to isolate mechanical faults.
  

Industry Insight: The Cost of Overlooking Pressure
Hydraulic pressure is the lifeblood of skid steer performance. While flow determines speed, pressure delivers power. Many operators focus on fluid levels and filter changes but overlook pressure diagnostics. Investing in a pressure gauge and understanding relief valve behavior can prevent costly downtime and misdiagnosis.
Final Thoughts
The Bobcat 773 remains a dependable machine when its hydraulic system is properly maintained. Weak lift performance is often a symptom of pressure loss—whether from a worn pump, faulty relief valve, or overlooked belt wear. By combining structured diagnostics with field wisdom, operators can restore full lifting power and extend the life of their machine.
As one veteran mechanic put it: “Hydraulics don’t lie—they just whisper until you learn to listen.”