Clark TMG 20 Power Steering Motor Failure and Diagnostic Strategy

[MikePhua]

Clark Forklifts and the TMG 20 Legacy
Clark Material Handling Company, founded in 1917 in Buchanan, Michigan, is credited with inventing the first industrial truck. Over the decades, Clark became a global leader in forklift manufacturing, with millions of units sold across more than 100 countries. The TMG 20 is part of Clark’s mid-range electric forklift series, designed for warehouse operations, light industrial use, and logistics centers. With a lifting capacity of approximately 2,000 kg and a compact chassis, the TMG 20 is favored for its maneuverability and low operating noise.
The TMG series integrates electric drive motors, regenerative braking, and hydraulic steering systems. Its power steering system, while efficient, depends on a dedicated electric motor and pump assembly to deliver hydraulic pressure to the steering cylinder. When this motor fails, steering becomes stiff or entirely unresponsive, compromising safety and productivity.
Understanding the Power Steering System
The Clark TMG 20 uses an electrically driven hydraulic power steering system. This setup includes:

• Electric Steering Pump Motor: Converts electrical energy into mechanical rotation to drive the hydraulic pump.
  
• Hydraulic Pump: Pressurizes fluid for steering actuation.
  
• Steering Cylinder: Converts hydraulic pressure into linear motion to turn the wheels.
  
• Pressure Relief Valve: Prevents over-pressurization of the system.
  
• Steering Control Valve: Directs fluid flow based on operator input.
  

Terminology annotation:

• Hydraulic Assist: A system where fluid pressure reduces the effort needed to steer.
  
• Electric Motor Drive: A motor powered by battery voltage, typically 24V or 36V in electric forklifts.
  
• Regenerative Braking: A system that recovers energy during deceleration and feeds it back into the battery.
  

Symptoms of Motor Failure
When the power steering pump motor fails, the most common symptoms include:

• No response from the steering wheel
  
• Audible clicking or humming from the motor housing
  
• Blown fuse or tripped circuit breaker
  
• Error codes on the forklift’s display panel (if equipped)
  
• Increased steering effort, especially under load
  

In one documented case, a Clark TMG 20 in Virginia exhibited complete steering loss during a pallet transfer. The operator noticed that the motor was silent and the hydraulic reservoir showed no fluid movement. After inspection, a corroded ground wire was found to be the root cause.
Diagnostic Procedure and Field Solutions
To diagnose a non-operating steering pump motor, follow these steps:

• Check battery voltage and confirm sufficient charge
  
• Inspect fuse panel for blown fuses related to steering motor
  
• Test continuity of motor wiring harness, especially ground and positive leads
  
• Apply direct voltage to the motor terminals to verify operation
  
• Inspect hydraulic fluid level and condition
  
• Examine motor brushes and commutator for wear or carbon buildup
  

If the motor fails to respond to direct voltage, it may require replacement. However, if wiring is the issue, repairs can be made using:

• Crimped terminals with heat shrink tubing
  
• Dielectric grease to prevent future corrosion
  
• Replacement of damaged wires with high-strand-count copper conductors
  

In a warehouse in Singapore, a technician resolved a similar issue by replacing a faulty relay that controlled the motor circuit. The relay had failed due to heat cycling and vibration, a common issue in high-usage environments.
Preventative Maintenance and Recommendations
To avoid steering motor failure, implement the following:

• Inspect electrical connections monthly
  
• Clean motor housing and ventilation ports to prevent overheating
  
• Replace hydraulic fluid every 1,000 operating hours
  
• Use OEM-grade relays and fuses for replacements
  
• Monitor motor amperage draw during operation to detect early signs of wear
  

For fleets operating in humid climates, additional sealing of connectors and periodic dielectric testing can prevent moisture-related failures.
Broader Context and Industry Trends
Electric forklifts like the TMG 20 are increasingly favored due to their low emissions and quiet operation. However, reliance on electric motors for auxiliary systems introduces new failure modes. Manufacturers are now integrating CAN-bus diagnostics and predictive maintenance algorithms to alert operators before critical failures occur.
In 2023, a logistics hub in Rotterdam reported a 12% reduction in downtime after implementing sensor-based monitoring on their electric forklifts’ steering systems. This data-driven approach is becoming standard in high-throughput facilities.
Conclusion
The Clark TMG 20’s power steering pump motor is a vital component that ensures safe and efficient operation. When it fails, the issue is often electrical in nature—wiring, fuses, or relays. With a structured diagnostic approach and preventative maintenance, operators can restore functionality and extend the life of the system. The TMG 20 remains a reliable partner in material handling, provided its systems are understood and cared for with diligence.