Diagnosing Steering Issues in the CAT 980G Wheel Loader

[MikePhua]

The 980G and Its Hydraulic Steering System
The Caterpillar 980G wheel loader, introduced in the late 1990s, was a major evolution in CAT’s mid-to-large loader lineup. With an operating weight of approximately 30 metric tons and a bucket capacity ranging from 5.5 to 7.0 cubic yards, the 980G was designed for quarrying, aggregate handling, and high-volume material movement. It featured a load-sensing hydraulic system, electronically controlled transmission, and improved cab ergonomics compared to its predecessor, the 980F.
One of the most critical systems in the 980G is its steering, which relies on hydraulic pressure and electronic feedback to deliver precise control. Unlike older mechanical linkages, the 980G uses a pilot-operated hydraulic steering valve and a priority valve to ensure steering remains responsive even under heavy load.
Terminology and Component Notes
- Pilot Valve: A low-pressure control valve that directs hydraulic flow to the main steering valve based on operator input.
- Priority Valve: A hydraulic component that ensures steering receives pressure before other functions, especially during simultaneous operations.
- Orbitrol: A steering control unit that converts mechanical input from the steering wheel into hydraulic signals.
- Steering Cylinder: A double-acting hydraulic cylinder mounted on the articulation joint, responsible for turning the loader’s frame.
- Feedback Sensor: An electronic device that monitors steering angle and assists in maintaining directional stability.
Symptoms of Steering Malfunction
Operators have reported difficulty steering left or right, with the steering wheel occasionally turning on its own. These symptoms suggest a loss of hydraulic control or erratic feedback from the orbitrol or pilot valve. In some cases, the loader may feel “locked” in one direction or require excessive effort to correct course.
Common indicators include:

• Steering wheel drifting without input
  
• Loader resisting turns or responding slowly
  
• Audible hydraulic whine during steering
  
• Inconsistent articulation speed
  
• Steering wheel returning to center too aggressively or not at all
  

Such behavior can be dangerous, especially in tight loading zones or when operating near haul trucks.
Root Causes and Diagnostic Approach
Several factors can contribute to steering issues in the 980G:

• Contaminated hydraulic fluid affecting valve response
  
• Internal leakage in the pilot valve or orbitrol unit
  
• Faulty priority valve failing to allocate pressure correctly
  
• Air intrusion in the steering circuit causing erratic movement
  
• Worn steering cylinder seals allowing bypass or drift
  

Diagnostic steps include:

• Checking hydraulic fluid level and condition
  
• Inspecting pilot valve for debris or wear
  
• Testing priority valve pressure output under load
  
• Bleeding the steering circuit to remove trapped air
  
• Verifying sensor signals and electronic feedback loops
  

One technician resolved a similar issue by replacing the orbitrol unit, which had developed internal leakage that caused the steering wheel to rotate independently of operator input.
Preventative Maintenance and Long-Term Solutions
To prevent steering failures and maintain system integrity:

• Replace hydraulic filters every 500 hours or as recommended
  
• Use CAT-approved hydraulic fluid with anti-foaming additives
  
• Inspect steering cylinder seals annually
  
• Monitor steering response during cold starts, when fluid viscosity is highest
  
• Keep electronic connectors clean and protected from moisture
  

In high-dust environments like quarries, steering components are especially vulnerable to contamination. Installing auxiliary filtration or relocating breathers can extend component life.
Caterpillar’s Loader Legacy and 980G Market Impact
Caterpillar has produced wheel loaders since the 1950s, with the 980 series becoming one of its most successful platforms. The 980G marked a transition toward electronically enhanced systems and improved operator comfort. Its success paved the way for the 980H and 980K, which introduced Tier 3 and Tier 4 emissions compliance, respectively.
Sales of the 980G were strong across North America, Europe, and the Middle East, particularly in mining and aggregate sectors. Its reputation for durability and performance made it a favorite among fleet managers and owner-operators alike.
Conclusion
Steering problems in the CAT 980G are often rooted in hydraulic or electronic control issues, not mechanical failure. By understanding the role of pilot valves, priority circuits, and orbitrol feedback, operators and technicians can diagnose and resolve steering anomalies effectively. In a machine built for precision and power, steering isn’t just a function—it’s a lifeline. And when the loader turns smoothly once again, it’s a testament to the value of experience, inspection, and informed repair.