Kobelco 150 Mark IV Track Drive Noise Often Caused by Worn Coupler or Sun Gear Splines

[MikePhua]

The Kobelco 150 Mark IV and Its Hydraulic Drive System
The Kobelco 150 Mark IV is a mid-size hydraulic excavator introduced in the early 1990s, designed for general earthmoving, trenching, and utility work. Kobelco, a Japanese manufacturer with a long history in construction machinery, built the Mark IV series to compete with models like the CAT 315 and Komatsu PC150. The 150 Mark IV features a closed-loop hydraulic system with independent travel motors driving each track, connected to planetary final drives through a short coupler shaft.
This configuration allows for high torque and smooth travel, but it also introduces potential wear points between the hydraulic motor and the final drive assembly—especially in machines operating in muddy or high-resistance terrain.
Symptoms of Drive Coupler Failure
Operators may notice a distinct clicking or clunking noise when attempting to move the machine in mud or under pressure. In some cases, the track will not rotate even though hydraulic pressure is applied. This behavior often mimics a “spline jump,” where the coupler or sun gear splines slip due to wear or misalignment.
A common diagnostic method involves placing the bucket against the track to apply resistance, then powering the travel motor. If the motor spins but the sprocket does not turn, the issue likely lies in the coupler or internal gear set.
Disassembly and Inspection Procedure
To inspect the drive components:

• Remove the outer cover of the final drive housing
  
• Extract the sun gear and inspect the spline teeth for rounding or wear
  
• Check the coupler behind the sun gear for signs of spinning or metal shavings
  
• If necessary, remove the hydraulic motor to access the planetary gear set
  

The planetary gears are timed to the ring gear, so reinstallation requires careful alignment. Brake disks and high-speed travel pistons must also be reassembled precisely to avoid performance issues.
Common Failure Points and Causes

• Coupler shaft wear: The short shaft between the hydraulic motor and final drive can wear over time, especially if lubrication is insufficient or alignment is off.
  
• Sun gear spline damage: Repeated torque under load can round off the splines, causing slippage.
  
• Loose drive lines: Steel drive lines may shift or vibrate, leading to misalignment and coupler fatigue.
  
• Contaminated lube oil: Metal particles in the oil indicate internal damage and should prompt immediate inspection.
  

One technician reported that draining the case lube revealed metallic residue, confirming internal wear. Another noted that the coupler spun freely inside the housing, a clear sign of spline failure.
Repair Cost and Complexity
Replacing the coupler and inspecting the planetary set is a moderate repair, typically requiring 6–8 hours of labor. Parts availability may vary depending on region and dealer support. Estimated costs:

• Coupler shaft: $400–$600
  
• Sun gear: $300–$500
  
• Seals and gaskets: $150–$250
  
• Labor (shop rate): $800–$1,200
  

Total repair cost can range from $1,500 to $2,500 depending on the extent of damage and whether the hydraulic motor needs servicing.
Preventive Measures and Recommendations
To extend the life of the drive system:

• Drain and inspect lube oil every 500 hours
  
• Monitor for unusual noises during travel, especially under load
  
• Avoid prolonged operation in deep mud without regular cleaning
  
• Use OEM-grade lubricants and torque specs during reassembly
  
• Keep detailed service records to track wear intervals
  

Conclusion
The Kobelco 150 Mark IV is a reliable excavator, but its track drive system can develop noise and slippage due to coupler or sun gear spline wear. Early diagnosis and careful disassembly are key to preventing further damage. With proper maintenance and attention to alignment, the machine can continue to perform effectively in demanding conditions.