Caterpillar High-Track Equalizer Bar Wear and Breakage Problems

[MikePhua]

Background of Caterpillar High-Track Undercarriage
Caterpillar’s high-track or high-drive dozers became prominent in the late 20th century, offering enhanced serviceability—the raised final drives keep them clear of debris and simplify replacements. This design also boosts track frame articulation and keeps wear on components like pads distributed more evenly. As a result, models like the D9R became highly popular across construction and mining industries, contributing notably to Caterpillar’s mid-size and large dozer sales—units whose sales ran in the thousands worldwide. This undercarriage style contrasted with older "oval track" designs, which used dead axles and swing frames—more cumbersome but simpler in geometry.
Equalizer Bar Function and Design
The equalizer bar (sometimes called the “hard bar”) links both track frames and transmits load forces while allowing limited oscillation. It replaces earlier spring-mounted systems and keeps the track frames aligned under heavy loads. Its ends are connected via spherical bushings, permitting slight angular motion and compensating for disparities in alignment.
Wear and Breakage Issues in High-Drive Dozers
Heavy-duty users have noticed that equalizer bars in high-track Caterpillar dozers often suffer premature wear or breakage—especially compared to low-track machines. One user reported breaking four to five bars over 10,000 hours on a D9R, an unusual frequency considering Caterpillar’s reputation for robustness.
What’s causing this?

• Overloading when dozing: Pushing the blade into the ground can lift the front of the machine and overstress the center bushing, which then overloads spherical end bushings.
  
• Insufficient lubrication: Ends are often buried in dirt and debris, hindering grease delivery—regardless of greasing intervals recommended.
  
• Harsh environmental conditions: One operator endured repeated failures while working in swift floodwaters over cobble stones—conditions that generated severe, repetitive stresses.
  
• Geometric challenges: Some mechanics struggled to conceptualize how rigid equalizer bars maintain alignment across varying machine positions, though small allowable movements in pivot shafts help accommodate the angles.
  

Solutions and Suggestions
Here’s a structured approach to reduce wear and breakage:

• Enhance lubrication: Add grease fittings (zerks) top and bottom of the bar’s ends to maintain consistent grease flow. Upgrade to an oil-bath lubrication system, which retains lubricant under challenging field conditions.
  
• Clean undercarriage routinely: Removing mud and debris helps lubricant reach seals and bushings. Caterpillar recommends clearing equalizer bar ends, pivot shafts, idlers, and rollers daily or as often as conditions demand.
  
• Alter operational technique: Avoid excessive blade plunging which tilts the machine, transferring load through sensitive points like the center bushing. Controlled dozing minimizes undue stress.
  
• Reinforce or redesign bushings: Some Komatsu machines switched to multi-layer rubber with steel sleeves for enhanced durability. Retrofit high-drive Cats with improved bushings, the slip-fit pins, or grease tracks modeled on these upgrades.
  
• Regular inspection: Monitor for pre-failure symptoms—such as blade pushing causing the front to rise while equalizer bars remain static—indicating bar or bushing damage.
  

Glossary

• Equalizer Bar (“Hard Bar”): Rigid bar linking track frames for load sharing and alignment while accommodating slight pivoting.
  
• High-Track (High-Drive): Dozer undercarriage design with elevated drive sprockets for improved component protection and service access.
  
• Spherical Bushings / Pivot Shaft: Components allowing slight angular motion while accommodating differential movement of track frames.
  
• Oil-Bath vs. Grease Lubrication: Grease relies on manual fills, while oil-bath encases parts in circulating oil for constant lubrication.
  
• Center Bushing Overextension: Occurs when blade action tilts machine forward, stressing central pivot bearings.
  

Real-World Example
An operator with a D9R dozer endured five equalizer bar failures over nearly 20,000 hours. Many occurred while doing emergency flood control in wet, cobble-strewn environments. He attributed the failures to extreme operational stress and concluded that the original design could not sustain such harsh conditions.
Summary
Caterpillar high-drive dozers offer mechanical advantages but expose equalizer bars to unique stresses. Failures commonly stem from overloading, poor lubrication, and harsh environments. Mitigation starts with improved grease/oil lubrication systems, maintenance discipline, and operational awareness. These enhancements can vastly extend component life and reduce costly downtime—ensuring that high-drive models remain durable and dependable in tough working conditions.