Restoring Hydraulic Performance in the John Deere 310B Backhoe

[MikePhua]

The 310B and Its Hydraulic System Design
The John Deere 310B backhoe loader, introduced in the early 1980s, was part of Deere’s second-generation compact construction lineup. Built for versatility in trenching, loading, and site prep, the 310B featured a mechanical transmission and a gear-driven hydraulic pump supplying fluid to both loader and backhoe circuits. With a hydraulic reservoir capacity of approximately 20 gallons and a system pressure near 2,250 psi, the machine was engineered for responsive control and reliable cycle times.
Its hydraulic system includes a sump screen, spin-on filter, relief valve assembly, and a series of directional control valves. Fluid is drawn from the transmission case, filtered, and pressurized before being distributed to the loader arms, bucket cylinders, outriggers, and boom functions.
Terminology annotation:

• Sump Screen: A mesh filter located in the reservoir that captures large debris before fluid enters the pump.
  
• Relief Valve: A spring-loaded valve that limits system pressure to prevent damage.
  
• Cycle Time: The duration required for a hydraulic function to complete a full movement, such as raising and lowering the boom.
  
• Chatter: A vibration or rattling sound caused by cavitation or inconsistent fluid flow in hydraulic components.
  

Symptoms After Fluid and Filter Service
Following a partial hydraulic fluid change—approximately 8 gallons drained and replaced with John Deere Hy-Gard—the machine exhibited sluggish response and severe chatter across all hydraulic functions. The loader and backhoe controls became erratic, and bubbles were observed on the dipstick, indicating aeration in the fluid. Despite proper fluid level and filter installation, the system failed to regain normal performance.
The operator also replaced a short rubber hose between the transmission case and the filter housing. This hose, submerged during filling, was suspected as a possible source of air ingress.
Root Cause and Valve Assembly Oversight
Upon further inspection, the issue was traced to the hydraulic filter assembly. During servicing, the technician had removed a plug at the bottom of the housing, unaware that it retained a spring-loaded relief valve. The spring had fallen into the drain pan and was retrieved, but the internal valve piston—critical for sealing the relief passage—was missing.
This valve, approximately 3/8" in diameter with a 3/16" stem, is held against its seat by the spring. Without it, the system allowed uncontrolled bypass of fluid, leading to pressure loss, aeration, and erratic behavior. Once the valve was recovered and reinstalled, the machine returned to normal operation with smooth control and full cycle speed.
Recommendations:

• Always identify and retain internal components during filter housing disassembly
  
• Use a magnetic pickup tool to recover dropped parts from drain pans
  
• Inspect relief valve springs for fatigue or deformation during service
  
• Confirm valve seating before startup to avoid cavitation and pump strain
  

Preventative Maintenance and Best Practices
To maintain hydraulic integrity in the 310B:

• Change hydraulic fluid every 1,000 hours or annually, whichever comes first
  
• Replace filters and inspect sump screens during each fluid change
  
• Use OEM-grade seals and gaskets to prevent air leaks at hose connections
  
• Bleed air from cylinders and lines after service by cycling functions slowly
  

Operators should also monitor fluid clarity and temperature during operation. Milky fluid indicates water contamination, while excessive heat may signal pump inefficiency or relief valve malfunction.
Field Anecdotes and Lessons Learned
In one similar case, a contractor servicing a 310C mistakenly installed a filter without its internal bypass valve. The machine exhibited identical symptoms—chatter, slow response, and aerated fluid. After replacing the valve assembly, performance normalized. This highlights the importance of understanding component function, especially in older machines where documentation may be limited.
Another technician shared that worn relief valve springs can mimic pump failure. Replacing a $10 spring restored full hydraulic pressure, saving thousands in unnecessary repairs.
Conclusion
Hydraulic issues in the John Deere 310B often stem from overlooked components during routine service. The relief valve assembly within the filter housing plays a critical role in maintaining system pressure and preventing aeration. By carefully inspecting and reinstalling internal parts, operators can avoid costly downtime and restore full functionality. In legacy equipment, attention to detail and mechanical intuition remain the most valuable tools in the shop.