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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.

Learn how we diagnose a weak final drive motor.

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

• Hydraulic Hoses and Final Drives
• CTL / MTL Undercarriage Basics
• Preventing Hydraulic Contamination

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.