How to Fix a Final Drive Oil Leak on the CAT D6B Dozer

[MikePhua]

CAT D6B Dozer Overview
The Caterpillar D6B is a mid-size crawler dozer introduced in the 1960s and produced through the early 1980s. Powered by the reliable CAT D333 diesel engine, it delivers around 140 horsepower and features a mechanical transmission, dead axle final drives, and a rugged undercarriage. The D6B was widely used in construction, forestry, and agriculture, and many units remain in service due to their rebuildable design and parts availability.
Caterpillar Inc., founded in 1925, has built millions of dozers globally. The D6B was part of its early elevated sprocket lineage, though it retained a conventional final drive layout. Its dead axle design means the sprocket is mounted on a tapered shaft, retained by a large nut and covered by a bolt-on housing.
Symptoms and Diagnosis of Final Drive Oil Leaks
A common issue with aging D6B units is oil leaking from the anterior side of the drive sprocket. This typically indicates a failed seal or bearing misalignment. Symptoms include:

• Visible oil seepage around the sprocket hub
  
• Oil loss from the final drive compartment
  
• Increased noise or vibration during operation
  
• Difficulty maintaining track tension
  

Before dismantling, it's essential to test for sprocket movement. Using a pry bar, check for lateral play. If movement is detected, the bearing preload may be incorrect, or internal wear may be present.
Terminology Notes

• Dead Axle: A non-driven axle that supports the sprocket and final drive components.
  
• Outboard Bearing: A bearing located outside the final drive housing, supporting the sprocket shaft.
  
• Tapered Shaft: A shaft with a conical profile that secures components via friction and a retaining nut.
  
• Spanner Wrench: A tool used to adjust slotted nuts on bearing assemblies.
  

Repair Procedure and Tooling Requirements
Repairing a final drive leak on the D6B requires heavy-duty tools and careful disassembly. Key steps include:

• Lift and Secure the Dozer: Use a 20-ton bottle jack and cribbing to support the frame. Apply wheel stops and secure the opposite track.
  
• Check for Sprocket Play: Use a pry bar to detect movement. If loose, adjust the slotted nut using a spanner wrench to factory torque specs.
  
• Remove the Final Drive Housing: Unbolt the outer cover and remove the retaining nut. The outboard housing must be pressed off using a 100-ton hydraulic press.
  
• Replace Seals and Bearings: Install new seals and inspect bearings for wear. Use OEM parts to ensure proper fit and longevity.
  
• Reassemble with Care: Align the tapered shaft and torque the retaining nut. Avoid damaging the new seal during installation.
  

Some operators have improvised with jacks and sledgehammers, but this is risky and may damage components. Professional shops or Caterpillar dealers have the correct press and tooling to perform the job safely.
Field Anecdote and Practical Insight
In Alabama, a mechanic repaired a leaking D6B final drive using blocks and a jack under the frame. He applied pressure and struck the sprocket with a sledgehammer to release the housing. While effective, he cautioned that this method requires experience and can damage seals if not done carefully.
In South Carolina, a backyard mechanic planned to lift the dozer, test for play, and adjust the bearing preload before dismantling. He emphasized safety and the importance of having a service manual to guide torque specs and assembly order.
Recommendations for Technicians and Owners

• Use Proper Lifting and Support Equipment: Safety is paramount when working under heavy machinery.
  
• Inspect Before Dismantling: Play in the sprocket may be resolved with bearing adjustment.
  
• Avoid Improvised Pressing Methods: Use a hydraulic press or consult a dealer for removal.
  
• Replace All Seals During Service: Prevent future leaks and ensure long-term reliability.
  
• Document Torque Specs and Assembly Steps: Helps during reassembly and future maintenance.
  

Final Thoughts
Final drive oil leaks on the CAT D6B are often caused by seal failure or bearing misalignment. With the right tools and methodical approach, the issue can be resolved safely. Whether using a press or relying on field techniques, attention to detail and proper torque settings are essential. The D6B remains a serviceable and dependable machine when maintained with care.