Komatsu D37 Track Tension Loss and Adjuster Cylinder Repair

[MikePhua]

The Komatsu D37EX-21A and Its Undercarriage System
The Komatsu D37EX-21A is a compact crawler dozer designed for grading, site preparation, and forestry work. Introduced in the early 2000s, it features a hydrostatic transmission, low ground pressure track system, and a sealed and lubricated undercarriage. Komatsu, founded in 1921, has produced millions of machines globally, with the D37 series becoming a staple in mid-size dozing applications due to its balance of power, maneuverability, and ease of maintenance.
The undercarriage includes a recoil spring and grease-filled hydraulic track adjuster cylinder that maintains proper track tension. This system allows the front idler to move forward under pressure, keeping the track taut during operation. When the adjuster fails, the track becomes loose, leading to derailment risk, accelerated wear, and reduced grading precision.
Symptoms of Track Tension Loss
Operators have reported that the left track on the D37EX-21A loses tension within minutes of operation, despite no visible grease leakage. This suggests an internal failure of the adjuster cylinder, where grease bypasses the piston seal and escapes into the recoil spring cavity or track frame.
Key symptoms include:

• Track slackening shortly after adjustment
  
• Idler retracting without external grease loss
  
• Difficulty locating the master pin or disassembling the track
  
• Confusion over part diagrams and seal identification
  

These issues point to a worn piston seal, damaged bushing, or loose grease fitting, all of which compromise the cylinder’s ability to hold pressure.
Diagnostic and Inspection Strategy
To confirm the fault:

• Adjust the track and mark the idler block position
  
• Operate the machine and observe idler movement
  
• Inspect the grease fitting and release valve for leaks
  
• Check for excessive wear in track rails and idler guides
  

If the idler retracts without visible grease loss, the cylinder is likely leaking internally. In some designs, escaping grease may fall between the rails, making detection difficult.
Disassembly and Seal Replacement
Repairing the adjuster requires:

• Locating and removing the master pin or solid master link
  
• Splitting the track at the idler end
  
• Backing the machine to relieve tension
  
• Removing the adjuster cylinder and recoil spring assembly
  

Key components to replace include:

• Piston seal (typically item 12 in diagrams)
  
• Bushing (item 2)
  
• Rod (item 18)
  
• O-rings and backup rings (items 15 and 16)
  

Avoid disturbing the large nut on the recoil spring, as it is under high tension. Use the old master pin as a guide during reassembly, and always install a new pin to ensure proper fit.
Track Disassembly Tips

• Look for a dimpled master pin facing outward
  
• If not visible, inspect from underneath the machine
  
• Burn out the ends of the pin with a torch and drive it out with a 4-pound hammer
  
• Remove pad bolts if using a solid master link
  

One technician shared that he split the track with the master at the idler, backed the machine slightly, and used the old pin for alignment during reassembly. This method reduced downtime and simplified the process.
Preventive Measures and Recommendations
To prevent future tension loss:

• Inspect adjuster seals annually
  
• Use high-quality grease with proper viscosity
  
• Monitor idler movement and track sag during operation
  
• Replace worn track components before they reach end-of-frame limits
  

Operators should also keep a parts diagram on hand and familiarize themselves with the adjuster assembly layout. Ordering seals and bushings in advance reduces repair delays.
Conclusion
Track tension loss in the Komatsu D37EX-21A is typically caused by internal leakage in the adjuster cylinder. With careful diagnostics, proper disassembly, and targeted seal replacement, the issue can be resolved effectively. Understanding the undercarriage design and mastering track disassembly techniques ensures long-term reliability and safe operation in demanding environments.