Switching Tracks on a CAT 977L Loader Undercarriage Wear Removal Techniques and Alignment Strategy

[MikePhua]

The 977L and Caterpillar’s Track Loader Legacy
The Caterpillar 977L crawler loader was introduced in the 1970s as part of CAT’s evolution in track-type loaders, designed to bridge the gap between dozers and excavators. With an operating weight exceeding 50,000 pounds and powered by a turbocharged six-cylinder diesel engine, the 977L delivered exceptional breakout force and stability for loading, ripping, and land clearing. Its hydrostatic drive and robust undercarriage made it a favorite in logging, demolition, and quarry operations.
Caterpillar, founded in 1925, had already established dominance in earthmoving equipment by the time the 977L was released. The L-series loaders featured improved hydraulic response, reinforced track frames, and better operator visibility compared to earlier models. Though production ceased decades ago, many 977Ls remain in service, especially in rural fleets and restoration projects.
Terminology Annotation:

• Crawler Loader: A tracked machine combining the lifting capability of a loader with the traction of a dozer.
  
• Breakout Force: The maximum force a bucket can exert to dislodge material.
  
• Hydrostatic Drive: A transmission system using hydraulic fluid to transfer power from engine to tracks.
  

Reasons for Track Replacement and Wear Indicators
Track replacement on a 977L is typically driven by:

• Excessive bushing wear or elongation
  
• Cracked or missing pads
  
• Sprocket hooking or tooth wear
  
• Track chain stretch beyond adjustment range
  
• Pin failure or seized links
  

Visual signs include:

• Uneven pad contact with the ground
  
• Track popping or jumping during turns
  
• Difficulty maintaining tension
  
• Increased vibration or noise from the undercarriage
  
• Hydraulic adjuster fully extended with sag still present
  

In one forestry loader in Oregon, a 977L began derailing during sidehill work. Inspection revealed that the track chain had stretched beyond spec, and the sprockets showed severe hooking. Replacing the tracks restored stability and reduced fuel consumption.
Preparation and Safety Before Track Removal
Removing tracks from a 977L requires planning, proper tools, and attention to safety. The machine must be immobilized and supported securely.
Preparation steps:

• Park on level ground and block the frame
  
• Relieve track tension by removing grease from the adjuster fitting
  
• Use heavy-duty cribbing to support the track frame
  
• Remove track guards and clean around the master pin
  
• Mark track orientation for reinstallation
  

Safety recommendations:

• Use eye protection and gloves during pin removal
  
• Avoid standing in the path of track recoil
  
• Keep bystanders clear of the work zone
  
• Use a hydraulic press or sledge with drift punch for pin extraction
  

Terminology Annotation:

• Master Pin: The removable pin that allows the track chain to be separated.
  
• Track Adjuster: A hydraulic mechanism that maintains track tension via grease pressure.
  
• Cribbing: Stacked blocks used to support heavy equipment during service.
  

In one demolition yard in Texas, a technician used a custom-built press to remove the master pin without damaging adjacent links. The job was completed in under two hours with minimal downtime.
Track Installation and Alignment Techniques
Installing new or rebuilt tracks requires careful alignment to prevent premature wear. Key steps include:

• Position the track around the sprocket and idlers
  
• Align the master pin holes using pry bars or chain hoists
  
• Insert the master pin with anti-seize compound
  
• Refill the adjuster with grease until proper sag is achieved
  
• Cycle the machine forward and backward to settle the chain
  

Recommended sag for the 977L is typically 1.5 to 2 inches at midpoint between rollers. Over-tightening can accelerate wear, while under-tensioning increases derailment risk.
Terminology Annotation:

• Anti-Seize Compound: A lubricant that prevents galling and corrosion on threaded or press-fit components.
  
• Track Sag: The vertical distance between the track and the top of the carrier roller, used to measure tension.
  
• Chain Hoist: A manual lifting device used to position heavy components.
  

In one grading crew in Alberta, improper alignment during installation caused the track to bind against the roller frame. After realignment and tension adjustment, the machine operated smoothly.
Undercarriage Component Inspection During Track Work
Track replacement is an ideal time to inspect other undercarriage components:

• Carrier rollers for flat spots or bearing noise
  
• Idlers for wear or misalignment
  
• Sprockets for tooth profile and engagement
  
• Track frame for cracks or weld fatigue
  
• Adjuster seals for leakage or contamination
  

Recommendations:

• Replace rollers and idlers in pairs to maintain balance
  
• Use OEM or high-quality aftermarket components
  
• Document wear measurements for future comparison
  
• Clean and repaint exposed metal to prevent corrosion
  

Terminology Annotation:

• Carrier Roller: A roller mounted above the track that supports the upper chain run.
  
• Idler: A wheel that guides the track and maintains alignment.
  
• Weld Fatigue: Cracking or failure of welded joints due to repeated stress cycles.
  

In one restoration project in Pennsylvania, a 977L’s track frame was found to have a hairline crack near the front idler mount. Welding and reinforcement plates were added before track installation.
Conclusion
Switching tracks on a CAT 977L is a demanding but rewarding task that restores traction, stability, and performance. With proper preparation, alignment, and inspection, the undercarriage can return to full service and extend the machine’s working life. In legacy iron, every pin and pad tells a story—and replacing them is a step toward keeping that story alive.