Restoring the Huber-Warco 10D Motor Grader with Cummins NHC-4

[MikePhua]

Origins of the Huber-Warco 10D
The Huber-Warco 10D motor grader is a product of two legacy American manufacturers: Huber Manufacturing and Warner & Swasey Company (Warco). Huber, founded in the mid-1800s in Marion, Ohio, was a pioneer in road-building machinery, producing some of the earliest steam-powered graders. By the 1960s, Huber had partnered with Warco to produce the 10D series, a mid-sized grader designed for municipal and private roadwork. These machines were known for their mechanical simplicity, robust steel frames, and compatibility with off-the-shelf diesel engines like the Cummins NHC-4.
Sales of the 10D peaked in the 1970s, with thousands delivered across North America. Though Huber ceased grader production in the 1980s, many units remain in service today, especially in rural areas where mechanical reliability trumps electronic sophistication.
Cummins NHC-4 Engine Characteristics
The Cummins NHC-4 is a naturally aspirated, four-cylinder diesel engine from the NH series, widely used in industrial and off-road applications. “NHC” designates:

• N: Naturally aspirated (no turbocharger)
  
• H: Horizontal inline configuration
  
• C: Compact variant
  

This engine typically produces around 120–140 horsepower at 2100 RPM, with a torque curve optimized for low-speed grading. It uses a PT (Pressure-Time) fuel injection system, which relies on a gear-driven pump and timed fuel delivery rather than electronic control.
Injection Pump Issues and Manual Shutoff Workaround
One of the quirks encountered in aging NHC-4 engines is fuel leakage into the crankcase. This occurs when the front seals of the PT injection pump degrade, allowing diesel to bypass into the engine oil. The result is diluted oil, reduced lubrication, and potential bearing damage.
In some field repairs, operators bypass the original electric shutoff solenoid by installing a manual needle valve on the pump body. This valve, often knurled for grip, is used to cut fuel flow manually. While functional, this workaround is not ideal. It introduces human error risk and does not prevent leakage when the engine is off.
Recommended solutions include:

• Removing and rebuilding the PT pump with new front seals
  
• Replacing the manual valve with a proper solenoid shutoff
  
• Monitoring oil viscosity and fuel contamination weekly
  

According to Cummins service bulletins, seal failure in PT pumps becomes common after 10,000 hours of operation or 15 years of service, whichever comes first.
Transmission Faults and Gear Loss
The 10D’s transmission is typically a manual 5-speed gearbox, often sourced from Clark or Fuller. Loss of second gear may result from:

• Worn synchronizers
  
• Broken gear teeth
  
• Shift fork misalignment
  
• Input shaft bearing failure
  

While second gear is useful for moderate grading slopes, its absence does not cripple the machine. Most operators rely on first and third gears for fine control and torque delivery. However, rebuilding the transmission is advisable if multiple gears begin to fail.
Anecdotally, a grader operator in British Columbia reported similar gear loss in a 10D2 unit. Upon teardown, the second gear cluster had fractured due to years of shock loading on steep terrain. The repair involved sourcing NOS (new old stock) gears from a salvage yard and replacing the input shaft bearings.
Brake System Overhaul
The brake system on the 10D is hydraulic, with drum brakes on each axle. Common issues include:

• Disconnected or corroded brake lines
  
• Seized wheel cylinders
  
• Leaking master cylinder
  
• Worn brake shoes
  

Given the age of most 10D units, a full brake system replacement is often necessary. Estimated parts and labor costs:

• Master cylinder: $150–$300
  
• Wheel cylinders (4): $400–$600
  
• Brake shoes: $200–$400
  
• Lines and fittings: $250
  
• Labor (20–30 hours): $2,000+
  

Total cost ranges from $3,000 to $4,000 depending on region and availability. For safety, especially on 7–10% grades, brakes must be fully functional before operation.
Estimated Weight and Transport Considerations
The Huber-Warco 10D weighs approximately 22,000 to 25,000 pounds (10–11 metric tons), depending on blade size and tire configuration. This places it in the mid-weight grader category, suitable for transport on a standard lowboy trailer. Operators should verify axle weights and secure permits for road transport, especially in jurisdictions with strict bridge laws.
Preservation and Legacy
Despite its age, the 10D remains a symbol of American mechanical engineering. Its simplicity allows for field repairs without specialized tools, and its compatibility with Cummins engines ensures parts availability. In 2021, a restored 10D was featured at the Marion County Historical Machinery Expo, drawing attention from enthusiasts and former Huber employees.
For those considering restoration, the 10D offers a rewarding challenge. With proper attention to the injection system, transmission, and brakes, it can serve reliably for years. Its legacy is not just in the roads it graded, but in the hands of those who keep it alive.