Why Does the John Deere 35G Slow Down While Traveling

[MikePhua]

John Deere 35G Compact Excavator Overview
The John Deere 35G is a 3.5-ton compact excavator introduced as part of Deere’s G-series lineup, designed for urban construction, landscaping, and utility work. With a 23.3 hp Yanmar diesel engine, zero-tail swing, and a maximum digging depth of 10 feet, the 35G balances maneuverability with performance. Deere, founded in 1837, has long been a leader in compact equipment, and the G-series machines have been widely adopted across North America and Asia for their reliability and ease of service. The 35G is particularly popular among rental fleets and owner-operators, with thousands of units sold since its launch.
Symptoms of Travel Speed Drop
Operators have reported a recurring issue where the 35G slows down while walking (traveling), especially on flat ground or slight inclines. The machine starts at normal speed but gradually decelerates. Interestingly, touching the left joystick—even slightly—causes the travel speed to recover temporarily. This cycle repeats, with the machine slowing again after a few seconds or minutes.
Additional symptoms include:

• Travel speed drop not linked to engine RPM
  
• Occasional drift to one side during movement
  
• Travel performance weaker when boom or arm is idle
  
• No fault codes or warning lights on the monitor
  

These behaviors suggest a hydraulic control issue rather than a mechanical failure.
Terminology Clarification

• Travel Flow Combiner Valve: A hydraulic component that merges flow from multiple pumps to maximize travel speed and torque.
  
• Control Valve: A central hydraulic valve block that directs flow to travel motors, boom, arm, and other functions.
  
• Joystick Signal: An electrical or pilot pressure input from the operator controls that triggers hydraulic valve actuation.
  
• Drive Motor: A hydraulic motor mounted on each track that converts fluid pressure into rotational movement.
  

Root Causes and Diagnostic Path
The most likely cause of intermittent travel slowdown is a malfunction or miscommunication within the control valve system. Specifically, the travel flow combiner valve may not be fully engaging unless the joystick is moved, which sends a signal to the valve block to prioritize travel.
Possible contributing factors:

• Weak or sticky spool in the control valve
  
• Electrical signal loss from joystick potentiometer
  
• Internal leakage in the combiner valve
  
• Drive motor wear or imbalance between left and right sides
  
• Software logic that deprioritizes travel when no other functions are active
  

In one case, a technician noted that the machine would drift to the right unless the operator arm was lifted. This indicated a flow imbalance, possibly due to a partially blocked passage or a misbehaving valve spool.
Recommended Troubleshooting Steps
To isolate and resolve the issue:

• Check hydraulic pressures at the travel motor ports during operation
  
• Inspect the travel flow combiner valve for debris or wear
  
• Test joystick signal output and confirm voltage or pilot pressure consistency
  
• Swap left and right drive motor hoses to see if the issue reverses
  
• Use diagnostic software to monitor valve actuation and travel priority logic
  
• Clean or replace control valve spools if sticking is suspected
  

If the issue persists, a dealer may recommend replacing the drive motor, but this should only be done after confirming that the control system is functioning correctly.
Operator Experience and Dealer Insight
A contractor in Quebec reported similar symptoms on a 27ZTS model. After consulting a dealer, he was advised that the machine might need a few hours of troubleshooting and was warned about the possibility of a drive motor replacement. However, the issue was ultimately traced to a faulty combiner valve that wasn’t fully engaging unless another function was activated. Replacing the valve resolved the travel slowdown without needing motor work.
Another operator in Pennsylvania noted that his 35G felt weak going uphill even with only 1,600 hours on the clock. While not dramatic, the performance drop was noticeable. After receiving technical documentation from a mechanic, he learned that the travel system relies heavily on valve coordination and joystick input—even minor signal loss can affect speed.
Preventive Measures and Long-Term Solutions
To maintain optimal travel performance on the 35G:

• Periodically flush the hydraulic system and replace filters
  
• Inspect joystick wiring and connectors for corrosion or wear
  
• Clean valve block surfaces and check for spool movement
  
• Avoid prolonged idling without function input, which may affect valve prioritization
  
• Use high-quality hydraulic oil and monitor for contamination
  

Conclusion
The John Deere 35G’s travel slowdown issue is typically rooted in hydraulic control logic, not mechanical failure. By understanding the role of the travel flow combiner valve and joystick signal coordination, operators and technicians can diagnose and resolve the problem without unnecessary component replacement. As compact excavators become more electronically integrated, subtle control behaviors like this will continue to challenge traditional troubleshooting—but with the right approach, they’re entirely manageable.