Spanish Tracked-Equipment Case: Hot Final-Drive Leakage Was Traced to Floating-Seal Face Loading After Gear and Bearing Checks Passed

The Final Drive Stayed Dry During Static Inspection

A tracked construction machine operating in Spain developed gear-oil leakage around the final-drive hub only after continuous travel.

When parked cold, the area could remain dry.

Short-duration movement also did not always reproduce the leak.

The symptom became more visible after the final drive had rotated for a longer period and reached operating temperature.

This temperature and rotation dependency narrowed the fault toward the dynamic sealing interface.

The Gear Train Was Checked Before the Seal Was Condemned

Inspection did not reveal a strong fault in:

• planetary gears;
• main bearings;
• housing structure;
• or basic oil level.

Because bearing play can disturb seal alignment, bearing condition was important to exclude before focusing only on the seal.

Floating Seals Work Differently From Static O-Rings

Many tracked final drives use a floating or Duo-Cone style mechanical face seal.

The simplified arrangement is:

Two precision seal rings → Faces run against each other → Elastomeric loading components position and load the rings

The sealing function depends on:

• face cleanliness;
• correct ring position;
• controlled contact loading;
• and stable supporting geometry.

If those conditions are incorrect:

Cold static joint may appear sealed → Rotation and heat change face behavior → Oil begins escaping

Cold and Hot Conditions Were Compared Directly

The machine was observed through:

• cold inspection;
• initial travel;
• extended travel;
• hot shutdown.

Leakage increased only after continued rotation.

That made a simple static O-ring leak less likely.

The key boundary became:

housing leaks because a stationary seal is damaged

versus

housing leaks because the rotating face seal loses correct contact during operation.

Seal Installation Condition Was Reviewed

Inspection of the floating-seal assembly focused on:

• seal-ring faces;
• elastomer seating;
• contamination;
• face scratches;
• ring position;
• housing contact areas;
• and evidence of uneven loading.

Improper handling or contamination of precision seal faces can influence performance even when the components appear visually installed.

Why Replacing Bearings Without Evidence Would Not Help

A worn bearing can affect seal alignment, but the bearings in this case did not show the evidence needed to explain the leak.

The diagnosis therefore remained at the rotating seal interface.

This avoided unnecessary work on the planetary gear system.

Repair and Verification

The face-seal system was restored using the machine manufacturer’s installation procedure.

After assembly, the final drive was tested through sustained travel to reproduce the original thermal condition.

The verification required more than a static leak check.

Case Takeaway

This Spanish tracked-equipment case demonstrates the value of comparing cold static sealing with hot dynamic sealing.

A final drive that stays dry while parked can still develop leakage when a floating mechanical seal loses correct face loading during rotation.

FAQ

Can a final-drive seal leak only when hot?

Yes. Dynamic face condition, thermal expansion and rotational behavior can make leakage appear mainly after operation.

Is a floating seal the same as a normal O-ring?

No. It is a mechanical face-sealing system with a different operating principle.