Diagnosing Auxiliary Hydraulic Issues on the Bobcat 853

[MikePhua]

The Bobcat 853 and Its Role in Compact Equipment History
The Bobcat 853 skid steer loader was introduced in the early 1990s as part of Bobcat’s push to expand its mid-size loader offerings. Manufactured by Melroe Company, which later became part of Doosan Infracore, the 853 featured a 58-horsepower Kubota V2203 diesel engine, a rated operating capacity of 1,700 pounds, and a vertical lift path ideal for loading trucks and handling palletized materials. Its auxiliary hydraulic system allowed operators to power attachments like augers, trenchers, and hydraulic breakers, making it a versatile tool across construction, landscaping, and agricultural sectors.
By the late 1990s, Bobcat had sold tens of thousands of 853 units globally. Many remain in service today, especially in rental fleets and owner-operated businesses. However, as these machines age, auxiliary hydraulic issues become increasingly common.
Terminology Clarification

• Auxiliary Hydraulics: A secondary hydraulic circuit used to power external attachments beyond the loader arms and bucket.
  
• Solenoid Valve: An electrically actuated valve that controls fluid flow in hydraulic systems.
  
• Coupler: A quick-connect fitting that allows hydraulic hoses to be attached or detached from the machine.
  
• Flow Control Switch: A toggle or button inside the cab that activates the auxiliary hydraulic circuit.
  

Common Symptoms of Auxiliary Hydraulic Failure
Operators often report that attachments do not respond when the auxiliary hydraulics are engaged. In some cases, the couplers hiss or leak, while in others, the solenoid clicks but no fluid flows. These symptoms point to a range of potential issues:

• No hydraulic pressure at the couplers
  
• Solenoid valve not activating
  
• Electrical switch failure
  
• Blocked or damaged hydraulic lines
  
• Internal valve sticking due to contamination
  

In one case, a contractor in Oregon attempted to run a trencher attachment but found no response. The couplers were clean, and the switch clicked audibly, but the attachment remained idle. After testing voltage at the solenoid and inspecting the valve body, the issue was traced to a stuck spool inside the auxiliary valve block.
Diagnostic Steps and Solutions
To resolve auxiliary hydraulic issues on the Bobcat 853:

1. Check Hydraulic Fluid Level: Low fluid can starve the auxiliary circuit. Use the sight gauge and top off with ISO 46 hydraulic oil if needed.
   
2. Inspect Couplers: Clean both male and female couplers. Replace O-rings if leaking. Ensure full engagement—partial connection can block flow.
   
3. Test Solenoid Function: Use a multimeter to verify voltage at the solenoid when the switch is activated. If voltage is present but no movement, the solenoid may be seized or the spool stuck.
   
4. Clean Valve Block: Remove the auxiliary valve and inspect for debris. Flush with clean hydraulic fluid and reinstall.
   
5. Check Electrical Switch: The toggle or button inside the cab may wear out. Replace if intermittent or unresponsive.
   
6. Inspect Hoses and Lines: Look for kinks, cracks, or internal collapse. Replace damaged sections and bleed the system to remove air.
   

Preventive Maintenance and Best Practices
To keep auxiliary hydraulics functioning reliably:

• Replace hydraulic filters every 500 hours
  
• Use clean, compatible fluid and avoid mixing brands
  
• Grease couplers monthly and store with dust caps
  
• Cycle auxiliary hydraulics weekly to prevent sticking
  
• Train operators to avoid deadheading attachments (holding flow open with no movement)
  

In 2016, a landscaping crew in Minnesota experienced repeated coupler failures during winter. The issue was traced to moisture ingress and freezing. After switching to stainless steel couplers and adding rubber caps, the problem disappeared.
Upgrades and Retrofit Options
For older Bobcat 853 units, consider:

• Installing a new auxiliary valve block with improved flow control
  
• Upgrading to electric-over-hydraulic switches for better responsiveness
  
• Adding a pressure gauge to monitor auxiliary output
  
• Retrofitting high-flow kits if using demanding attachments like cold planers
  

Conclusion
Auxiliary hydraulics are the lifeline of attachment versatility on the Bobcat 853. When they fail, productivity suffers. By understanding the system’s components—solenoids, couplers, valves, and switches—operators and technicians can diagnose issues efficiently and restore full functionality. With proper maintenance and occasional upgrades, even a decades-old 853 can continue powering attachments with precision and reliability.