John Deere 490 Excavator: Diagnosing Starter Engagement Failures and Solenoid Behavior

[MikePhua]

Introduction
The John Deere 490 “straight” excavator, a legacy model from the late 1980s and early 1990s, is known for its mechanical simplicity and rugged build. However, as these machines age, electrical issues—particularly starter engagement failures—can become increasingly common. This article explores a real-world diagnostic journey involving intermittent starter operation, solenoid clicking, and suspected wiring faults. Through detailed analysis, terminology clarification, and field anecdotes, we’ll unpack the challenges and solutions surrounding this issue.
Understanding the Starting Circuit
The starting system in the Deere 490 includes several key components:

• Ignition switch
  
• Starter solenoid
  
• Starter motor
  
• Relay (possibly mounted near the boom or firewall)
  
• Battery and ground cables
  
• Wiring harness and connectors
  

When the ignition key is turned, the solenoid should engage, allowing current to flow to the starter motor and crank the engine.
Terminology Clarified

• Solenoid: An electromechanical switch that connects battery power to the starter motor when energized.
  
• Bendix Drive: A gear mechanism that engages the starter pinion with the engine flywheel.
  
• Clicking: The audible sound of the solenoid engaging but failing to transmit current to the starter motor.
  
• Shorting Terminals: Manually bridging the solenoid terminals with a screwdriver to bypass the ignition circuit.
  
• Intermittent Fault: A sporadic issue that appears inconsistently, complicating diagnosis.
  

Symptoms and Initial Observations
Operators reported the following:

• Solenoid clicks every time the key is turned, but starter does not engage.
  
• Original solenoid occasionally starts the engine after 5–10 clicks.
  
• Jumping the solenoid terminals with the key in the “on” position causes the starter to crank normally.
  
• Two replacement solenoids click but never engage the starter.
  
• Cleaning and shimming terminals inside the solenoid did not resolve the issue.
  

These symptoms suggest that the solenoid is receiving signal but not transmitting sufficient current to the starter motor—possibly due to internal resistance, weak current supply, or mechanical binding.
Field Anecdote: New York Operator’s Troubleshooting Journey
An operator in New York faced persistent starter issues with his Deere 490. After replacing the solenoid twice and cleaning terminals, he found that manually shorting the solenoid terminals allowed the starter to crank reliably. This pointed toward a weak ignition signal or internal solenoid fault. He speculated whether a relay mounted behind the boom might be interfering with current flow.
Case Study: Voltage Drop and Starter Tap Test
A technician in Wisconsin recommended using a multimeter to measure voltage at the starter side of the solenoid while holding the key in the “start” position. If voltage drops significantly or fluctuates, it may indicate poor contact or internal resistance. He also suggested tapping the starter motor with a screwdriver handle while holding the key—an old-school trick to free stuck brushes or a seized Bendix drive.
Possible Causes of Starter Engagement Failure

• Weak Ignition Signal
  A worn ignition switch or corroded wire may deliver insufficient current to energize the solenoid fully.
  
• Internal Solenoid Resistance
  Even new solenoids can have manufacturing defects or poor contact surfaces.
  
• Bendix Binding
  A partially seized Bendix drive may prevent the solenoid from fully engaging the starter gear.
  
• Relay Malfunction
  A secondary relay between the ignition switch and solenoid may be clicking but failing to transmit current.
  
• Ground Faults
  Corroded or loose ground cables can reduce current flow and cause intermittent engagement.
  

Best Practices for Diagnosis

• Use a multimeter to measure voltage at solenoid terminals during key activation
  
• Inspect and clean all ground connections, including battery and chassis grounds
  
• Test ignition switch output for consistent voltage
  
• Manually engage the Bendix drive to check for mechanical binding
  
• Trace wiring from ignition switch to solenoid and relay for breaks or corrosion
  

Anecdote: The Solenoid That Wouldn’t Quit
In Ontario, a mechanic replaced a solenoid three times before discovering that the starter motor itself had worn brushes and a sticky Bendix. The solenoid was clicking properly, but the starter couldn’t engage. After rebuilding the starter, the machine started flawlessly—proving that even persistent clicking doesn’t guarantee solenoid failure.
Conclusion
Starter issues in the John Deere 490 excavator often stem from a combination of electrical and mechanical faults. While solenoid clicking suggests partial engagement, true diagnosis requires voltage testing, mechanical inspection, and a methodical approach. With patience and the right tools, operators can restore reliable starting performance and keep these legacy machines working hard. In the world of heavy iron, even a simple click can tell a complex story.