Diagnosing Hydraulic Sluggishness in the Bobcat 843 Skid Steer

[MikePhua]

The Bobcat 843 and Its Hydraulic Legacy
The Bobcat 843 skid steer loader was introduced in the late 1980s as part of Bobcat’s push into mid-frame machines with higher horsepower and hydraulic flow. Powered by a 54-hp diesel engine and equipped with a gear pump hydraulic system, the 843 was designed for general construction, grading, and material handling. Though discontinued, it remains in use across farms and job sites due to its mechanical simplicity and robust frame.
Its hydraulic system powers both the drive motors and the lift/tilt functions. Unlike modern machines with pilot controls and load-sensing hydraulics, the 843 uses direct mechanical linkages and open-center hydraulics, which can become sluggish or unresponsive when components wear or fluid conditions degrade.
Terminology Notes

• Open-Center Hydraulic System: A design where fluid flows continuously through the control valves until a function is activated.
  
• Hydraulic Levers: Mechanical linkages that actuate spool valves to direct fluid to cylinders or motors.
  
• Hydraulic Resistance: Increased effort required to move control levers, often caused by internal friction or pressure imbalance.
  
• Bucket Flick: A rapid tilt movement used to dump material quickly; sluggish response here indicates low flow or valve restriction.
  

Reported Symptoms and Initial Observations
Operators have reported heavy resistance on the drive levers and slow lift/tilt response, even with the engine throttled up and fluid levels full. The machine struggles to flick the bucket or perform quick movements, suggesting a systemic hydraulic issue rather than isolated cylinder failure.
This behavior points to one or more of the following:

• Restricted flow through the control valve block
  
• Contaminated or aerated hydraulic fluid
  
• Worn pump or internal leakage
  
• Clogged return or suction filters
  

Diagnostic Path and Common Faults

1. Check Hydraulic Fluid Condition
   Old or contaminated fluid can thicken and reduce flow. Inspect for discoloration, cloudiness, or metal particles. Replace fluid if degraded.
   
2. Inspect Filters and Screens
   The 843 has a suction screen in the reservoir and a return filter. If clogged, these can starve the pump or restrict flow. Clean or replace as needed.
   
3. Test Pump Output
   Use a pressure gauge to measure output at the lift circuit. Normal operating pressure should be around 2,000 psi. If low, the pump may be worn or bypassing internally.
   
4. Examine Control Valve Linkages
   Stiff levers may result from rusted pivot points or bent rods. Lubricate all joints and verify full spool travel.
   
5. Check for Air in the System
   Aeration can cause spongy response and cavitation. Bleed the system and inspect for loose fittings or cracked hoses.
   

Recommendations for Restoration

• Flush and replace hydraulic fluid every 500 hours or annually
  
• Clean suction screen and replace return filter during fluid service
  
• Lubricate all mechanical linkages monthly
  
• Install a pressure gauge port for ongoing diagnostics
  
• Avoid overloading the system with oversized attachments or excessive cycle times
  

Conclusion
Hydraulic sluggishness in the Bobcat 843 is often a result of fluid degradation, filter blockage, or pump wear. By following a structured diagnostic approach and maintaining the system proactively, operators can restore responsiveness and extend the life of this classic skid steer. Though mechanically simple, the 843’s hydraulic system demands attention to detail—especially as it ages in the field.