Shop Talk Blog

Most owners and operators don’t realize how important case drain flow is when evaluating and diagnosing a final drive motor. This test can tell you a great deal about what’s going on inside your final drive without having to open it up.

In this blog post, we take a look at case drain flow testing, including how to perform the test and how to interpret the results.

Internal Leakage

Internal leakage is designed to support lubrication and cooling of dynamic components (e.g., bearings, pistons, etc.). Now, this leakage never leaves the system. It will always be returned to the hydraulic reservoir, often via a low-pressure drain line. Internal leakage does not contribute to the work being done by the final drive motor, though.

There is a baseline case for the hydraulic motor drain flow on your machine. However, as wear increases internal clearances and internal seals wear out, the case drain flow increases. This directly reduces the final drive's volumetric efficiency.

In the world of compact equipment, even the most seemingly minor component can make or break your machine’s performance. One such part, frequently overlooked but absolutely essential, is the case drain filter. It is a low-profile workhorse hidden in your hydraulic system, and when neglected, it can lead to catastrophic damage to your final drive motor.

At Texas Final Drive, we’ve seen the aftermath of ignored or clogged case drain filters: cracked housings, shredded rotator groups, and thousands of dollars in repairs. Here’s what every equipment owner and operator needs to know about this vital component.

Here are a few Shop Talk blog posts you might be interested in:

• Identifying the Hydraulic Ports on a Final Drive Motor
• Bobcat Final Drive Failures and Case Drain Filters
• Preventing Case Drain Related Failure on Final Drive Motors

Here are some final drive motor horrors from our own shop -- with some explanations of what caused them and how you can prevent them.

And while you're here, check out these terrifying Shop Talk Blog posts from the past ...

• Compact Equipment and Dinosaur Parks
• Skid Steers and Zombies

Why don't we see case drain filters on all compact hydraulic equipment? There are pros and cons to including them in the hydraulic design. If your machine requires one, then it is critical that you replace it regularly.

Here are some other Shop Talk Blog posts you may find useful:

• Troubleshooting a Final Drive Using Case Drain Flow
• Bobcat Final Drive Failures and Case Drain Filters
• Preventing Case Drain Related Failures
  

A good number of the failed Bobcat final drive motors we see come in are related to the case drain filter. Here's why -- and how to keep it from happening to you!

Here are a few other Shop Talk Blog posts you might be interested in:

• Just the Facts about Case Drain Filters
• Bobcat 325 Rotator Group Damage
• Autopsy: Bobcat 331 Mini-Excavator Final Drive

One way to troubleshoot a final drive that seems weak is to take a look at the rate of flow from the case drain line. In this Shop Talk Blog post, we are going to review the purpose of a case drain line, look at what case drain flow can tell us about a final drive, and then discuss how to estimate the case drain flow. We'll finish up by looking at how to evaluate the case drain flow to determine if the problem is your final drive.