Diagnosing Steering Shake in the CAT 980B Wheel Loader

[MikePhua]

The Legacy of the CAT 980B
The Caterpillar 980B wheel loader, introduced in the early 1970s, was a cornerstone of heavy material handling for over a decade. Built with a focus on mechanical simplicity and brute strength, it featured a 3408 V8 diesel engine, planetary powershift transmission, and robust Z-bar linkage. Thousands of units were sold globally, and many remain in service today, particularly in quarries, snow removal fleets, and bulk material yards. However, as these machines age, certain mechanical symptoms—like steering shake—become more common and require nuanced diagnosis.
Understanding Steering Shake and Its Root Causes
Steering shake refers to a rhythmic or erratic vibration in the steering wheel or front frame during turning, often more pronounced in one direction. In the 980B, this issue is typically more noticeable during left turns and may be accompanied by audible clunks or resistance in the steering effort.
Key components involved in the steering system include:

• Follow-up linkage: A mechanical feedback system that ensures the steering valve returns to neutral after input.
  
• Steering valve: A hydraulic directional control valve that regulates flow to the steering cylinders.
  
• Center pins: Pivot points in the articulation joint that bear the load and guide movement.
  
• Centering spring: A spring-loaded mechanism inside the follow-up linkage that helps re-center the steering.
  
• Deck mounts: Structural supports that, if loose, can amplify vibration.
  

Common Failure Points and Symptoms

• Worn follow-up linkage: Causes delayed or erratic valve response, leading to overcorrection and oscillation.
  
• Sticky centering spring: If rusted or seized, it prevents smooth return to center, especially in cold or wet environments.
  
• Loose or corroded washers: Found at the ends of the centering spring, these can bind and restrict movement.
  
• Improper linkage adjustment: Incorrect length or anchor position can cause the steering arc to overshoot or undershoot.
  
• Loose deck or articulation bolts: Can introduce frame flex, making steering feel unstable.
  

In one snow removal fleet in Ontario, a 980B exhibited severe shake during left turns. After replacing the upper center pin with minimal improvement, technicians discovered the follow-up linkage spring was rusted solid. Once cleaned and re-lubricated, steering response improved dramatically.
Adjustment and Repair Procedures

1. Inspect the follow-up linkage
   • Remove the floor panel to access the linkage.
     
   • Check for free movement and spring tension.
     
   • Clean and lubricate all pivot points.
     
2. Replace or rebuild the steering valve
   • If internal wear is suspected, install a remanufactured valve.
     
   • Ensure all hydraulic lines are flushed to prevent contamination.
     
3. Adjust linkage geometry
   • Move the anchor ball away from the center pin to reduce steering arc.
     
   • Adjust the follow-up length to center the arc and prevent hitting stops.
     
   • Fine-tune the box-to-valve link to balance steering effort in both directions.
     
4. Check articulation and deck mounts
   

• Torque all bolts to spec.
  
• Inspect for frame cracks or bushing wear.
  

Safety Precautions

• Never run the engine with the follow-up or valve linkage disconnected.
  
• If the valve is actuated without feedback, the steering box can be damaged.
  
• Always depressurize the hydraulic system before disassembly.
  

Final Thoughts
Steering shake in the CAT 980B is often a cumulative result of wear, corrosion, and misadjustment. While replacing center pins may offer partial relief, the root cause frequently lies in the follow-up linkage and steering valve. With careful inspection, proper lubrication, and precise adjustment, even a decades-old 980B can regain smooth, predictable steering. For operators and mechanics alike, understanding the mechanical feedback loop in this classic loader is key to keeping it productive and safe.