Diagnosing and Restoring Steering Clutches and Brakes on the Komatsu D20A Dozer

[MikePhua]

The Komatsu D20A and Its Compact Dozing Heritage
The Komatsu D20A is part of Komatsu’s compact crawler dozer lineup, designed for light grading, site prep, and agricultural work. Introduced in the late 1970s and continuing through the 1980s, the D20A featured a hydrostatic transmission, a small but efficient diesel engine, and a mechanical steering clutch and brake system. Its compact footprint and maneuverability made it popular in tight spaces and on soft terrain.
Komatsu, founded in Japan in 1921, became a global leader in earthmoving equipment by the 1980s. The D-series dozers, including the D20A, were widely exported and remain in use today, especially in rural and restoration settings. Despite their age, many units are still serviceable thanks to robust mechanical design and rebuildable components.
Terminology and Component Notes
- Steering Clutch: A friction-based assembly that disengages drive to one track, allowing the machine to pivot.
- Brake Band: A curved friction surface that clamps onto a drum to halt track movement.
- Adjuster Bolt: A threaded rod used to tension the brake band against the drum.
- Brake Shoe: The contact surface that presses against the drum when braking is engaged.
- Final Drive Housing: The casing that contains the steering clutch, brake assembly, and drive gears.
Symptoms and Initial Observations
After rebuilding the steering clutches and brakes on a D20A, one operator found that while the clutches worked perfectly, the brakes failed to engage. Tightening the brake adjuster bolt caused it to bottom out without applying pressure to the drum. The adjuster was confirmed to be hooked onto the brake shoe, suggesting that the issue lay deeper within the brake assembly.
Common symptoms of brake failure include:

• No resistance when pulling the brake lever
  
• Machine continues to move even with brake engaged
  
• Adjuster bolt turns freely without increasing tension
  
• Brake band appears loose or misaligned inside the housing
  

Possible Causes and Diagnostic Strategy
Several factors can lead to ineffective braking after reassembly:
- Incorrect brake band installation
If the band is not seated properly around the drum, tightening the adjuster will not apply pressure. Ensure the band is centered and the ends are correctly positioned in their anchor points.
- Worn or missing friction material
Older brake bands may have degraded linings, reducing contact area. Inspect the band for thickness and replace if below spec.
- Improper adjuster engagement
The adjuster bolt must hook securely onto the brake shoe or anchor tab. If misaligned, it may bottom out without tensioning the band.
- Drum wear or contamination
Oil or rust on the drum surface can prevent friction. Clean thoroughly and inspect for scoring or pitting.
- Incorrect reassembly of linkage
The brake lever linkage must transmit full travel to the band. Check for bent rods, missing bushings, or misadjusted clevis pins.
Recommended Solutions and Rebuild Tips
To restore braking function:

• Remove the final drive cover and inspect the brake band alignment
  
• Verify that the adjuster bolt is threading into the correct anchor point
  
• Replace the brake band if friction material is worn or delaminated
  
• Clean the drum surface with brake cleaner and scuff lightly with emery cloth
  
• Reassemble with proper torque and test lever travel before sealing the housing
  

Use OEM or high-quality aftermarket brake bands rated for Komatsu D-series dozers. Avoid generic bands that may not match curvature or anchor geometry.
Preventative Maintenance and Long-Term Reliability
To maintain steering and braking performance:

• Adjust brake bands every 250 hours or quarterly
  
• Inspect linkage and pivot points for wear and lubrication
  
• Replace seals in the final drive housing to prevent oil contamination
  
• Use correct gear oil and monitor for leaks around the brake drum
  
• Exercise the brakes regularly to prevent rust buildup
  

One technician shared that after rebuilding both sides on a D20A, he found that one brake worked while the other didn’t—due to a misaligned band end that had slipped off its anchor. After repositioning and retensioning, both brakes engaged smoothly.
Conclusion
Rebuilding the steering clutches and brakes on a Komatsu D20A is a rewarding task that restores maneuverability and safety. While the clutches may respond immediately to proper installation, the brakes require careful alignment, clean surfaces, and correct tensioning. With methodical inspection and attention to mechanical detail, even vintage dozers like the D20A can return to full operational strength. In compact earthmoving, control is everything—and the brake band is the final word.