Diagnosing and Adjusting Track Tension on Caterpillar Track Loaders

[MikePhua]

Track Tensioning Systems and Their Mechanical Principles
Track tensioning is a critical maintenance procedure for tracked loaders, especially models like the Caterpillar 973 and 955L. These machines rely on a grease-filled hydraulic cylinder housed within the track adjuster assembly to maintain proper tension between the front idler and the drive sprocket. The system is designed to absorb shock, reduce wear, and prevent derailment during operation.
Terminology:

• Track adjuster: A spring-loaded or hydraulic mechanism that maintains track tension
  
• Idler: A non-powered wheel guiding the track at the front of the undercarriage
  
• Guard: A structural bracket securing the idler to the track frame, often with multiple mounting positions
  
• Relief valve: A pressure release mechanism that prevents over-tensioning
  

The standard procedure involves driving the machine slowly to a stop without braking, removing the access hatch, and injecting grease into the tensioning cylinder via a zerk fitting. As grease enters the cylinder, it pushes the piston forward, extending the idler and tightening the track.
Common Symptoms of Tensioning Failure
Operators may encounter situations where grease enters the fitting but the track remains slack. This typically indicates one of the following:

• Internal seal failure within the adjuster cylinder
  
• Grease bypassing the piston and filling voids behind it
  
• The adjuster reaching its mechanical limit without further extension
  
• Misalignment or wear in the idler mounting guard
  

In one case, a 973 loader showed persistent slack despite repeated greasing. Inspection revealed that the idler mount was at the rear-most position on the guard bracket, meaning the adjuster had reached its maximum travel. The solution was to reposition the guard to its forward mounting holes, compensating for pin and bushing wear.
Mechanical Adjustment and Guard Repositioning
The idler guard typically features six bolt holes, allowing for two distinct mounting positions. By moving the guard forward, the idler is repositioned closer to the sprocket, restoring tension range. This adjustment is especially useful when track components have worn but are not yet ready for replacement.
Adjustment steps:

• Remove the three bolts securing the guard to the track frame
  
• Shift the guard to the forward set of holes
  
• Reinstall bolts and torque to specification
  
• Recheck track sag and tension
  

If the guard is already in the forward position and tension cannot be restored, the next step is to remove a track link. This shortens the overall track length and allows the adjuster to operate within its effective range.
Rebuilding the Track Adjuster Assembly
Over time, seals within the grease-filled cylinder degrade, allowing grease to leak past the piston and accumulate in dead zones. Rebuilding the adjuster involves disassembling the cylinder, replacing seals, and cleaning internal surfaces.
Rebuild procedure:

• Remove the adjuster from the track frame using manufacturer instructions
  
• Disassemble the piston and cylinder components
  
• Replace all seals with OEM or high-quality aftermarket kits
  
• Reassemble and test for pressure retention
  

One technician rebuilding a 955L adjuster noted that the process was straightforward once the unit was removed. The key challenge was accessing the cylinder without disturbing the spring assembly, which stores considerable force.
Preventative Maintenance and Inspection Protocols
To extend the life of the track tensioning system:

• Inspect track sag weekly during active use
  
• Grease the adjuster monthly or after heavy operation
  
• Monitor idler alignment and guard bolt integrity
  
• Replace seals every 2,000–3,000 hours or as needed
  

Proper tension reduces wear on pins, bushings, and sprockets. It also improves fuel efficiency by minimizing friction and slippage. In forestry applications, where debris and mud can clog the undercarriage, tensioning becomes even more critical.
Conclusion
Track tensioning on Caterpillar loaders is both a preventative and corrective task. Whether adjusting grease pressure, repositioning guards, or rebuilding cylinders, the goal is to maintain optimal alignment and reduce component stress. With attention to detail and timely intervention, operators can ensure smooth operation and extend the life of their undercarriage. In the world of tracked machines, tension isn’t just mechanical—it’s the difference between control and chaos.