Rebuilding a John Deere 310A After Hydraulic Pump Catastrophe

[MikePhua]

The John Deere 310A and Its Mechanical Legacy
The John Deere 310A backhoe-loader was introduced in the late 1970s as part of Deere’s expanding line of compact construction equipment. Built for versatility and durability, the 310A featured a mechanical transmission, open-center hydraulic system, and a naturally aspirated diesel engine. It became a staple for municipalities, contractors, and farm operators across North America. With thousands sold during its production run, the 310A earned a reputation for reliability—though like any aging machine, it’s not immune to catastrophic failures.
Terminology annotation:

• Open-center hydraulic system: A type of hydraulic circuit where fluid flows continuously through the system until a valve is actuated.
  
• Harmonic balancer: A component attached to the crankshaft that reduces torsional vibration and protects engine internals.
  
• Keyway: A machined slot in a shaft that accepts a key to lock rotating components together.
  
• Deadheading: A hydraulic condition where fluid is pumped against a closed valve, causing pressure spikes and potential damage.
  

The Incident and Initial Diagnosis
While idling into position for routine cleanup, the operator of a 310A heard a loud squeal followed by a snap. The engine continued running, but smoke began rising from the front. Upon inspection, the fan, balancer, and hydraulic pump were no longer rotating. The machine had lost all hydraulic function—including steering—and had to be muscled back into the shed.
Disassembly revealed a broken harmonic balancer and a severely damaged keyway on the crankshaft. More critically, the hydraulic pump had seized completely. The question arose: did the pump failure cause the balancer to fail, or vice versa?
Pump Disassembly and Internal Damage
Upon opening the pump, the damage was extensive. Broken bearing races, shattered needle bearings, and fractured internal components filled the housing. It looked as though the pump had exploded internally. Surprisingly, there were no signs of heat damage—suggesting mechanical failure rather than thermal seizure.
One theory was that a cracked piston inside the pump had wedged between the cam and housing, locking the shaft. Another possibility was a pressure spike due to deadheading or regulator failure. Regardless, the pump was beyond repair.
Crankshaft and Balancer Repair Strategy
The crankshaft’s keyway was widened by about 50%, but the snout itself remained intact. Rather than replacing the crankshaft—a costly and labor-intensive job—the operator opted to machine a new balancer slot to accept a wider key. This approach preserved the engine and avoided unnecessary teardown.
It’s worth noting that the crank snout on the 310A is straight, not tapered, and the balancer is not press-fit. It slides on and is secured by a bolt, simplifying reinstallation.
Pump Coupling and Drive System Observations
Interestingly, all pump drive components—including the cast iron coupler, aluminum drive plates, and plastic isolator—were in excellent condition. On earlier models, Deere used a split coupling with rubber bushings; later versions employed a rubber damper donut. These systems are designed to fail before damaging the crankshaft, but in this case, the pump seized so violently that the balancer and crankshaft took the brunt.
A similar failure was reported by another operator whose pump drive shaft snapped cleanly without warning. The aluminum coupling and rubber insert remained intact, suggesting fatigue or internal pump failure as the root cause.
System Flush and Contamination Control
After such a catastrophic pump failure, flushing the hydraulic system is essential. Metal fragments can travel downstream into valves, cylinders, and hoses. At least two complete flushes are recommended, using clean fluid and filters each time. Operators should disconnect hoses and blow them out into clean buckets to assess contamination levels.
If metal is found beyond the pump outlet, further disassembly may be required. Fortunately, the 310A’s open-center system is relatively simple, and many components are accessible without full teardown.
Reassembly and Operational Recovery
Following the pump replacement, the operator rebuilt the engine, inspected and resealed the clutch packs, and removed the reverse brake for inspection. After bleeding the fuel system, the machine started and ran smoothly. The rebuilt pump performed flawlessly, and the 310A returned to service.
This recovery underscores the resilience of older Deere machines. With mechanical systems and field-serviceable components, even catastrophic failures can be overcome with patience and ingenuity.
Preventive Measures and Recommendations
To avoid similar failures:

• Monitor hydraulic pressure and temperature regularly
  
• Replace fluid and filters at recommended intervals
  
• Avoid deadheading the pump during operation
  
• Inspect couplings and balancers for wear or misalignment
  
• Keep the front of the engine clean to spot leaks or smoke early
  

For legacy machines like the 310A, sourcing rebuilt pumps from reputable vendors is often more practical than chasing NOS parts. In this case, a rebuilt unit from Kintech proved reliable and cost-effective.
Conclusion
The John Deere 310A may be decades old, but its mechanical simplicity and robust design make it a viable workhorse even today. When a hydraulic pump seizes and damages the crankshaft, the repair may seem daunting—but with careful diagnosis, creative machining, and thorough system flushing, recovery is possible. This story is a testament to the enduring value of classic equipment and the determination of those who keep it running.