Hydraulic Troubleshooting and System Behavior on the John Deere 35G

[MikePhua]

The 35G and John Deere’s Compact Excavator Lineage
John Deere’s 35G compact excavator is part of the G-series, designed for versatility in tight spaces while maintaining the hydraulic power needed for trenching, grading, and utility work. Introduced in the mid-2010s, the 35G quickly became a favorite among contractors and municipalities due to its zero-tail swing design, intuitive controls, and compatibility with a wide range of attachments.
John Deere, founded in 1837, has long been a leader in agricultural and construction equipment. By the time the 35G entered production, Deere had already sold hundreds of thousands of compact excavators globally. The 35G was engineered to meet Tier IV Final emissions standards while delivering smooth hydraulic performance in a sub-4-ton package.
Core Specifications and Hydraulic System Overview
The 35G is powered by a Yanmar 3TNV88F diesel engine producing approximately 23.3 horsepower. It features a load-sensing hydraulic system with variable displacement pumps, allowing precise control and efficient flow distribution.
Key specifications:

• Operating weight: ~3,500–3,800 kg
  
• Max digging depth: ~3.1 m
  
• Bucket breakout force: ~3,300 kgf
  
• Hydraulic flow: ~60 L/min
  
• Auxiliary hydraulic circuit: ~38 L/min
  
• Swing speed: ~9 rpm
  

The hydraulic system uses pilot controls to actuate the main control valve, which directs flow to the boom, arm, bucket, and travel motors. The system is designed to prioritize simultaneous functions, such as swinging while lifting, without sacrificing responsiveness.
Symptoms of Hydraulic Malfunction and Field Observations
Operators have reported issues such as:

• Boom or arm movement slowing or stalling under load
  
• Bucket curl functioning normally while other circuits lag
  
• Hydraulic whine or cavitation sounds during operation
  
• Travel motors working but digging functions failing
  
• No visible leaks or fault codes on the monitor
  

In one trenching job in Ontario, a 35G began losing boom lift capacity after warming up. The operator noted that the bucket curled with full force, but the boom would hesitate or stop mid-stroke. After inspection, the issue was traced to a sticking spool valve and a partially collapsed suction hose.
Root Causes and Diagnostic Strategy
Hydraulic faults in the 35G often stem from:

• Contaminated fluid causing valve spool sticking
  
• Air ingress through cracked suction hoses or loose fittings
  
• Internal leakage in cylinders or control valves
  
• Pilot pressure loss due to clogged screens or faulty sensors
  
• Priority valve malfunction affecting flow distribution
  

Recommended diagnostic steps:

• Check hydraulic fluid level and condition (look for cloudiness or metallic sheen)
  
• Inspect suction and return hoses for soft spots or cracks
  
• Test pilot pressure at the control valve (should be ~25–30 bar)
  
• Use infrared thermometer to detect hot spots in valve block
  
• Remove and clean spool valves if sticking is suspected
  
• Verify auxiliary circuit isolation if attachments are connected
  

In one municipal fleet in Georgia, a 35G exhibited intermittent boom failure. The root cause was a loose ground wire affecting the pilot solenoid signal. After securing the connection and flushing the fluid, the machine returned to normal operation.
Terminology Notes

• Pilot Pressure: Low-pressure hydraulic signal used to actuate main control valves.
  
• Spool Valve: A sliding valve that directs hydraulic flow to specific functions.
  
• Cavitation: The formation of vapor bubbles in hydraulic fluid due to low pressure, which can damage pumps.
  
• Priority Valve: A valve that ensures critical functions receive hydraulic flow before secondary circuits.
  
• Suction Hose: A low-pressure hose that feeds fluid from the reservoir to the pump.
  

Preventive Measures and Long-Term Reliability
To maintain hydraulic performance:

• Replace hydraulic fluid every 1,000 hours or annually
  
• Change filters every 500 hours or sooner in dusty environments
  
• Inspect hoses quarterly and replace any showing surface cracks
  
• Clean pilot screens and check solenoid connectors during scheduled service
  
• Use OEM-grade fluid with anti-foaming and anti-wear additives
  

In one landscaping fleet in California, switching to synthetic hydraulic oil and installing magnetic drain plugs reduced valve failures by 40% and extended service intervals by 25%.
Operator Experience and Field Adaptations
Operators appreciate the 35G’s smooth controls and compact footprint. Features include:

• Adjustable wrist rests and ergonomic joystick layout
  
• LCD monitor with maintenance reminders and fault alerts
  
• Auxiliary hydraulic switch on the right joystick
  
• Auto-idle and auto-shutdown for fuel savings
  

Some crews retrofit additional features:

• Hydraulic thumb kits for material handling
  
• Quick couplers for fast attachment changes
  
• LED lighting for night trenching
  
• Telematics systems for fleet tracking and diagnostics
  

In a utility upgrade project in Shanghai, a 35G was used to excavate around live water lines. The operator noted that the machine’s fine control and low noise profile allowed work to proceed without disturbing nearby residents.
Final Thoughts
The John Deere 35G is a compact powerhouse, but its hydraulic system demands clean fluid, solid connections, and consistent maintenance. When boom or arm functions falter while other circuits remain strong, the issue often lies in pilot pressure, spool behavior, or suction integrity. With methodical diagnostics and preventive care, the 35G can deliver precision and reliability across seasons and job sites. In compact excavation, smooth hydraulics are more than convenience—they’re the heartbeat of the machine.