Case Drain Filters

We’ve talked about issues with case drain filters before, and here we have another example of a final drive that was severely damaged because of just that problem.

The trouble begins when a case drain filter isn’t changed. The image below shows a case drain filter that needs to be changed. The filters should be a gold or bronze color, and when they begin to look like this is when they need to be replaced.

When a filter is clogged like this one, hydraulic fluid can no longer flow through it, and thus the case drain line ends up blocked. This causes a build-up of pressure in the hydraulic side of the drive. As that pressure continues to build, it will damage the lower shaft seal, also known as the oil seal. This is the seal around the drive shaft that separates the hydraulic fluid from the gear oil.

Once the oil seal is damaged, hydraulic fluid is allowed to mix with the gear oil. This only serves to relieve the pressure temporarily, however. More hydraulic fluid is forced into the gear side of the drive, and keep in mind that there is not supposed to be any pressure on that side. In this particular final drive, this increasing pressure blew the cover off the lower shaft bearing.

The cover plate on the final drive cracked. This customer was lucky that a cracked cover plate was the worst thing that happened. Some customers have had their cover plates rocket off the final drive at high speed, which can damage not only equipment, but also personnel.

Here is another final drive that experienced a case drain filter related failure. As you can see, the oil seal is blown in the image below.

When the inside of the cover plate was inspected, it was found to be covered in brass shavings. Brass shavings on the gear side of the final drive is never a good thing.

Conclusion: Final Drive Routine Maintenance Needed

The neglect of the inexpensive, fairly straightforward maintenance routine of checking and the changing the case drain filter ended up costing this customer quite a bit of money in repairs. Never neglect the maintenance on your final drive!