Wiring the Destroke Solenoid on a John Deere 310B

[MikePhua]

The John Deere 310B and Its Hydraulic Evolution
The John Deere 310B backhoe loader was introduced in the early 1980s as part of Deere’s expanding utility equipment lineup. Built for versatility in construction, agriculture, and municipal work, the 310B featured a mechanical diesel engine, open-center hydraulics, and a robust frame capable of handling both digging and loading tasks. With an operating weight of around 13,000 pounds and a backhoe dig depth exceeding 14 feet, it became a staple in North American fleets.
John Deere, founded in 1837, had by then established itself as a leader in both agricultural and construction machinery. The 310B was part of the second generation of the 310 series, following the original 310 and preceding the 310C. Thousands of units were sold, and many remain in service today due to their mechanical simplicity and ease of repair.
Understanding the Destroke Solenoid
At the heart of the 310B’s hydraulic system is a front-mounted gear-type hydraulic pump driven directly by the engine crankshaft. To reduce engine load during startup, the pump is equipped with a destroke solenoid—a small electrical device that temporarily reduces hydraulic pressure, allowing the engine to crank more easily.
Key terminology includes:
- Destroke Solenoid: An electrically actuated valve that unloads the hydraulic pump during engine start-up.
- Starter Relay Terminal: A junction point where electrical signals are distributed during the cranking cycle.
- Ground Circuit (06): A designated return path for electrical current, typically bolted to the flywheel housing or frame.
- 20A Wire: A wire connected to the starter relay, energized only during cranking.
The solenoid is energized only when the engine is cranking. Once the engine starts, the solenoid deactivates, allowing full hydraulic pressure to resume.
Wiring the Solenoid Correctly
The solenoid has two wires: one hot and one ground. The hot wire should be connected to the starter relay terminal that receives power from the ignition switch during cranking—commonly labeled as wire 20. This ensures the solenoid is only active during startup. The ground wire should be connected to the machine’s chassis, ideally at the flywheel housing where the 06 ground circuit terminates.
Incorrect wiring can lead to continuous energization of the solenoid, which may cause overheating, reduced hydraulic performance, or premature failure. In one case, a technician discovered the hot wire had been incorrectly connected to the alternator, keeping the solenoid energized at all times. The ground wire was broken and unconnected, rendering the system ineffective.
Testing and Precautions
Before reconnecting the solenoid, it’s essential to test its integrity:

• Use a multimeter to check continuity across the coil
  
• Measure resistance to ensure it matches manufacturer specifications
  
• Apply power briefly and listen for a clicking sound, indicating actuation
  
• Never energize the coil when it’s removed from the pump body, as it may overheat
  

If the solenoid fails to click or shows no continuity, it may be burned out and require replacement. Always verify that the coil is seated properly before applying voltage.
Field Anecdotes and Practical Advice
One operator in North Carolina purchased a used 310B and noticed two loose wires near the hydraulic pump. After tracing the wires and consulting diagrams, he realized they belonged to the destroke solenoid. With help from experienced technicians, he rewired the solenoid to the starter relay and grounded it properly. The machine’s cold-start performance improved immediately.
Another mechanic in Wisconsin noted that some early 310B models used a 6V solenoid, which could be damaged by full 12V power. He recommended checking voltage ratings before wiring and avoiding resistors unless specified by the manufacturer.
Recommendations for Reliable Operation
To ensure proper function of the destroke solenoid:

• Confirm voltage rating before wiring
  
• Connect hot wire to starter relay terminal energized during cranking
  
• Ground securely to flywheel housing or designated chassis point
  
• Test solenoid for continuity and actuation before installation
  
• Avoid energizing coil when detached from pump
  

If the solenoid is damaged or unavailable, some operators temporarily bypass it by manually destroking the pump during cold starts. However, this is not recommended for long-term use, as it increases engine load and wear.
Conclusion
The destroke solenoid on the John Deere 310B is a small but vital component that ensures smooth engine starts by reducing hydraulic resistance. Proper wiring—hot to the starter relay and ground to the chassis—is essential for reliable operation. With careful inspection, correct voltage matching, and routine testing, this system can continue to support the 310B’s hydraulic performance for years to come. In legacy equipment, understanding the interplay between electrical and hydraulic systems is key to keeping machines productive and dependable.