Caterpillar 922A Loader Structural Wear Hydraulic Tube Repair and Axle Trunnion Adjustment

[MikePhua]

The 922A and Caterpillar’s Mid-Size Loader Legacy
The Caterpillar 922A was introduced in the early 1960s as part of CAT’s push to expand its wheel loader lineup for municipal, agricultural, and light construction use. With an operating weight around 17,000 pounds and powered by a naturally aspirated diesel engine, the 922A offered a balance of maneuverability and lifting power. It featured a mechanical transmission, open-center hydraulics, and a rigid frame design with front-wheel drive—typical of loaders from that era.
Caterpillar, founded in 1925, had already established dominance in earthmoving equipment by the time the 922A was released. The model became popular in county road departments and small contractors, known for its simplicity and long service life. Tens of thousands were sold globally, and many remain in use today, especially in rural fleets and restoration circles.
Terminology Annotation:

• Wheel Loader: A machine with a front-mounted bucket used for loading, grading, and material transport.
  
• Open-Center Hydraulics: A system where fluid flows continuously through the valve until a function is activated.
  
• Trunnion: A pivot point or bearing that supports rotational movement, often found in axle assemblies.
  

Wear-Induced Hydraulic Tube Damage
After decades of operation, structural wear can lead to unexpected failures. In one case, the front drive axle of a 922A rubbed against a steel hydraulic tube feeding one of the boom lift cylinders. This type of contact is typically caused by:

• Excessive play in the axle trunnion bushings
  
• Sagging cylinder mounts due to worn anchor points
  
• Frame flex under load causing misalignment
  
• Vibration-induced fatigue in unsupported tubing
  

Symptoms include:

• Hydraulic fluid leaks near the lift cylinder base
  
• Reduced lifting power or slow boom response
  
• Visible scoring or deformation on the tube surface
  
• Oil spray or mist during operation
  

In one grading crew in Nebraska, a 922A began losing lift pressure during cold starts. Inspection revealed a pinhole leak in the steel tube caused by axle contact. The operator patched the tube with a TIG weld and shimmed the trunnion, restoring full function.
Repair Strategy and Welding Considerations
Repairing a steel hydraulic tube in place requires precision and awareness of pressure ratings. TIG welding is preferred for thin-wall steel due to its control and low heat input.
Steps include:

• Drain hydraulic fluid and depressurize the system
  
• Clean the damaged area with solvent and wire brush
  
• Clamp the tube to prevent movement during welding
  
• Use ER70S-2 filler rod for mild steel compatibility
  
• Weld in short passes to avoid overheating adjacent seals
  
• Pressure test the system after repair to confirm integrity
  

Terminology Annotation:

• TIG Welding: Tungsten Inert Gas welding, a process using a non-consumable tungsten electrode for precise welds.
  
• ER70S-2: A filler metal suitable for welding mild steel with good ductility and strength.
  
• Pressure Test: A diagnostic procedure where hydraulic fluid is pressurized to check for leaks or weak welds.
  

In one municipal loader in Michigan, a technician used TIG welding to patch a tube near the steering valve. After testing at 2,500 psi, the repair held without seepage.
Axle Trunnion Shimming and Cylinder Anchor Adjustment
To prevent future contact, the axle trunnion and cylinder anchor points must be realigned. Excessive play in the trunnion allows the axle to shift under load, especially during turns or uneven terrain.
Recommendations:

• Measure trunnion bushing wear with feeler gauges
  
• Install steel or brass shims to restore factory clearance
  
• Inspect anchor bolts and bushings for elongation or cracking
  
• Use torque specs from the original service manual during reassembly
  
• Grease pivot points to reduce vibration and wear
  

Terminology Annotation:

• Feeler Gauge: A tool used to measure gap width between components.
  
• Shim: A thin piece of material used to fill space and restore alignment.
  
• Anchor Point: The fixed mounting location of a hydraulic cylinder or structural member.
  

In one restoration project in Oregon, a 922A’s axle was shimmed with custom-cut stainless steel plates. The loader regained steering precision and eliminated tube contact.
Preventative Measures for Aging Loaders
To extend the life of legacy machines like the 922A:

• Inspect hydraulic lines quarterly for abrasion or flex fatigue
  
• Replace trunnion bushings every 2,000 hours or during overhaul
  
• Use rubber grommets or clamps to isolate tubes from vibration
  
• Monitor lift cylinder alignment during boom cycles
  
• Keep a log of structural inspections and repairs
  

In one forestry loader in British Columbia, implementing a preventative inspection checklist reduced hydraulic failures by 60% and extended cylinder life by over 1,500 hours.
Conclusion
The CAT 922A remains a testament to mechanical simplicity and durability—but age introduces wear that demands attention. When axle movement threatens hydraulic integrity, welding repairs and trunnion adjustments restore function and prevent cascading damage. In vintage iron, longevity is earned through vigilance—and every shim, weld, and inspection keeps the legacy alive.