When a Final Drive Leak is Neglected

Have you ever had a leak in your final drive?

Introduction and Diagnosis

This is a Comer final drive from Bobcat 331 mini-excavator. The customer initially noticed that the drive was leaking behind the sprocket, indicating a leaking face seal. Installing new face seals are fairly straightforward, so this in and of itself is not a major repair.

Results

If this happens to you, though, your initial instinct will probably be to top off the fluid and wait for a more convenient time to see what kind of repairs might be in order. The problem with that is that is when gear oil or hydraulic fluid can get out of a final drive, that means abrasive contaminants like mud and sand can get in. When a seal fails, it means much more than the inconvenience of a leak.

This customer waited too long to get the repairs done, and it cost him. If this final drive had come in with a leaking face seal it would have been fixed in about one day and shipped back to the customer.

However, because the leak was ignored, the customer now has a completely trashed final drive that simply needs to be replaced. You can see the thick sludge all over the planetary gear set below.

The bearings are blown, the gears are damaged, and the entire gearbox is filled with a thick, chunky sludge where there should simply be gear oil. The gears below are just caked in sludge.

What Not To Do

Sometimes customers think the best thing to do is to pack the housing with grease, believing that it will lubricate the bearings and fix the issue — but this is not the case. Packing the planetary portion of the drive with grease is never recommended because it actually causes more problems for a leaking drive motor. It results in even more friction, leads to catastrophic planetary failure, and the drive will fail in just a matter of time.

Conclusion

When you detect a leak in your final drive, you will save money in the long run by getting the seals replaced immediately – otherwise, you might end up with a destroyed final drive. Taking the time to address the little things can often prevent the more major, time-consuming, expensive repairs.