CAT D6B Track Walking Issues and Undercarriage Alignment Solutions

[MikePhua]

The CAT D6B and Its Mechanical Legacy
The Caterpillar D6B crawler tractor was introduced in the 1960s as part of Caterpillar’s mid-size dozer lineup, designed for grading, pushing, and land clearing. Built with mechanical simplicity and rugged durability, the D6B featured a direct drive transmission, open-center hydraulics, and a robust undercarriage system. It was powered by the reliable CAT D333 diesel engine, producing around 140 gross horsepower, and quickly became a staple in forestry, road building, and agricultural development.
Caterpillar, founded in 1925, had already established dominance in the track-type tractor market. The D6B was a transitional model between the earlier cable-operated machines and the more advanced hydraulic and electronically controlled dozers that followed. Tens of thousands of units were sold globally, and many remain in use today, especially in regions where mechanical simplicity is preferred over digital complexity.
Understanding Track Walking and Its Causes
Track walking refers to the tendency of a crawler machine to drift or pull to one side during operation. In severe cases, it can lead to the machine walking out of its tracks entirely, causing derailment, downtime, and potential damage to the undercarriage.
Terminology notes:

• Track Frame Alignment: The geometric relationship between the left and right track frames. Misalignment causes uneven tension and directional pull.
  
• Equalizer Bar: A pivoting bar that connects the track frames and allows vertical movement. Worn bushings or pins can shift alignment.
  
• Carrier Rollers: Located on top of the track frame, they guide the track chain and prevent sag. Missing or seized rollers can cause side drift.
  
• Track Tension: The preload applied to the track chain via a recoil spring and grease cylinder. Uneven tension leads to instability.
  
• Sprocket and Idler Wear: Uneven wear patterns can cause the track to ride improperly, especially during turns or under load.
  

Common causes of walking out of tracks:

• Bent or misaligned track frames
  
• Uneven track tension between sides
  
• Worn equalizer bar bushings or pivot pins
  
• Missing or damaged carrier rollers
  
• Excessive wear on sprockets, idlers, or track links
  
• Operating on steep side slopes or soft ground
  

In one case, a land-clearing crew in Arkansas reported repeated derailments on their D6B while working on a sloped clay embankment. After inspection, they discovered the left track frame was bent inward by nearly 1.5 inches due to a previous impact. Realignment and replacement of the equalizer bar bushings resolved the issue.
Inspection and Diagnostic Strategy
To identify the root cause of track walking:

• Measure Track Frame Alignment
  Use a laser or string line to check parallelism between left and right frames. Any deviation over 0.5 inches should be corrected.
  
• Check Equalizer Bar Movement
  Lift the machine and inspect for excessive play in the pivot. Replace worn bushings and pins.
  
• Inspect Carrier Rollers
  Spin each roller manually. Replace seized or missing units. Ensure mounting bolts are tight.
  
• Verify Track Tension
  Measure sag at mid-point between idler and sprocket. Adjust grease cylinder to achieve recommended tension (typically 1–1.5 inches of sag).
  
• Examine Sprocket and Idler Wear
  Look for cupping, sharp edges, or uneven tooth wear. Replace components if wear exceeds 25% of original profile.
  
• Check Track Chain Condition
  Inspect for stretched links, cracked bushings, or side wear. Replace worn chains or rotate pins and bushings if reversible.
  

In 2022, a contractor in British Columbia rebuilt the undercarriage of his D6B after repeated walking issues. He replaced both track frames, installed new carrier rollers, and upgraded to sealed and lubricated track chains. The machine returned to full service with improved stability and reduced wear.
Preventive Maintenance and Operating Tips
To minimize track walking and extend undercarriage life:

• Grease track tension cylinders every 100 hours
  
• Inspect equalizer bar monthly for movement and wear
  
• Clean track frames and rollers to prevent mud buildup
  
• Avoid sharp turns on steep slopes or soft terrain
  
• Alternate turning directions to balance wear
  
• Use wide track shoes in swampy or loose soil conditions
  

Operators should be trained to recognize early signs of misalignment, such as uneven blade tracking, increased fuel consumption, or difficulty maintaining straight lines during grading.
Repair Solutions and Component Recommendations
When repairing track walking issues:

• Use OEM or high-quality aftermarket bushings and pins for equalizer bar
  
• Replace track frames only with factory-spec units or precision-fabricated replacements
  
• Upgrade to sealed carrier rollers for reduced maintenance
  
• Install wear strips or guides to improve chain tracking
  
• Consider undercarriage conversion kits for improved performance on older machines
  

In 2023, a forestry operator in Maine retrofitted his D6B with a modern undercarriage system sourced from a D6C donor machine. The upgrade included sealed rollers, reinforced track frames, and a hydraulic tensioning system. The result was smoother operation and reduced derailment risk during hillside logging.
Conclusion
Track walking in the CAT D6B is often a symptom of deeper undercarriage misalignment, wear, or tension imbalance. While the machine’s mechanical design is robust, decades of use can introduce subtle shifts that compromise stability. With careful inspection, targeted repairs, and consistent maintenance, operators can restore proper tracking and extend the life of this iconic dozer. The D6B remains a testament to Caterpillar’s engineering legacy—provided its tracks stay true to the path ahead.