Caterpillar D6M Grease System Failures and Track Frame Lubrication Strategy

[MikePhua]

The D6M and Its Undercarriage Design
The Caterpillar D6M dozer was introduced in the mid-1990s as part of CAT’s evolution of the D6 series, offering improved visibility, modular components, and enhanced undercarriage durability. With an operating weight of approximately 18 metric tons and powered by a CAT 3306 turbocharged diesel engine producing around 165 horsepower, the D6M was designed for grading, ripping, and general earthmoving. One of its key features was the pivot shaft and track frame lubrication system, which relied heavily on consistent greasing to prevent wear and maintain alignment.
CAT’s elevated sprocket design, used on the D6M, reduces shock loads to the final drives but places greater emphasis on proper lubrication of the pivot shaft and equalizer bar bushings. Neglecting grease points can lead to premature wear, misalignment, and costly repairs.
Terminology Note

• Pivot Shaft: A central shaft connecting the track frames to the mainframe, allowing vertical movement and absorbing ground shock.
  
• Equalizer Bar: A transverse bar that balances load between the left and right track frames.
  
• Grease Zerk: A fitting used to inject grease into a bearing or bushing.
  
• Track Frame: The structural assembly that supports the track rollers, idlers, and sprockets.
  

Symptoms of Grease System Failure
Operators of the D6M have reported the following issues:

• Grease purging from unexpected locations during lubrication
  
• Inability to build pressure at certain zerks
  
• Grease exiting near the pivot shaft instead of traveling through the equalizer bar
  
• Excessive play in the track frame bushings
  
• Audible creaking or knocking during turns or grading
  

These symptoms suggest blocked passages, worn seals, or misrouted grease channels. In one case, a contractor in Alberta noticed grease exiting near the pivot shaft cap rather than traveling through the equalizer bar. After disassembly, they found hardened grease blocking the internal passage and a missing seal ring.
Root Causes and Diagnostic Strategy
Common causes of grease system failure include:

• Hardened Grease: Over time, grease can dry out and form plugs, especially if incompatible types are mixed.
  
• Seal Failure: Worn or missing seals allow grease to escape before reaching the intended bushing.
  
• Improper Grease Type: Using low-viscosity or non-tackified grease can result in poor adhesion and migration.
  
• Blocked Passages: Dirt, rust, or hardened grease can obstruct internal channels.
  
• Incorrect Greasing Technique: Over-pressurizing or under-greasing can damage seals or leave bushings dry.
  

To diagnose:

• Remove the pivot shaft cap and inspect for hardened grease or debris
  
• Use a bore scope to inspect internal grease passages
  
• Test each zerk with a manual grease gun and monitor flow
  
• Replace seals and O-rings as needed
  
• Flush passages with solvent-compatible grease if blockage is suspected
  

Recommended Grease and Lubrication Practices
For the D6M pivot shaft and equalizer bar:

• Use CAT’s recommended grease or an equivalent NLGI Grade 2 lithium complex with molybdenum disulfide
  
• Grease every 10–50 hours depending on operating conditions
  
• Apply grease slowly to avoid seal blowout
  
• Monitor for purge at the opposite end of the bushing to confirm flow
  
• Avoid mixing grease types unless compatibility is verified
  

Operators should also clean zerks before greasing to prevent contamination and replace damaged fittings immediately.
Anecdote from the Field
In 2021, a grading crew in Georgia experienced excessive wear on the left track frame of their D6M. Grease was exiting near the pivot shaft but not reaching the equalizer bar. After removing the shaft and cleaning the internal passages with a flexible solvent wand, they discovered a hardened plug of incompatible grease. Switching to a high-tack moly grease and replacing all seals restored proper flow. The machine returned to service with improved articulation and reduced noise.
Manufacturer History and Design Evolution
Caterpillar’s D6 series has been in production since the 1930s, with the D6M representing a transitional model between mechanical and electronically controlled dozers. The elevated sprocket design introduced in the 1980s improved final drive longevity but required more attention to undercarriage lubrication.
Later models like the D6N and D6T introduced automatic lubrication systems and improved seal designs. However, the D6M remains popular in owner-operator fleets due to its mechanical simplicity and parts availability.
Recommendations for Fleet Managers and Technicians

• Train operators on proper greasing intervals and purge observation
  
• Keep seal kits and grease fittings in inventory
  
• Document lubrication history and track wear patterns
  
• Use color-coded grease guns to prevent cross-contamination
  
• Schedule undercarriage inspections every 500 hours
  

Conclusion
Grease system failures in the Caterpillar D6M often stem from hardened grease, seal wear, or blocked passages. By understanding the flow path, selecting the correct grease, and maintaining disciplined lubrication practices, operators can prevent costly undercarriage damage and extend machine life. The D6M remains a reliable workhorse when its pivot shaft and equalizer bar are properly maintained—proving that even the toughest machines depend on the smallest details.