Just got your new or reman final drive motor and are having a little trouble identifying the ports? This Shop Talk Blog post is for you.

In this blog post, we’ll go over the four different categories of ports you can find on a final drive, what their purpose is, and how to identify them. For larger tonnage motors, we’ve also included a short video we made.

Here are some additional Texas Final Drive blog posts you might find helpful:

• Valve Blocks on Final Drive Hydraulic Motors
• The Ultimate Glossary of Terms About Hydraulic Motors
• What to Know Before You Order a Final Drive
  
  

Overview of the Ports on a Final Drive Motor

Let’s take a look at the ports you can find on a final drive motor:

• Flow and Return Ports, A and B
• Case Drain Ports, C1 and C2
• Brake Port, b
• Dual-Speed or Multi-Speed Port

A minimum of two hydraulic ports will always be present: A and B.

Flow and Return Ports (A and B)

These are the largest ports and will always be present in matching pairs. The A and B ports are the forward and reverse input ports. They’re usually the largest ports you’ll see on a final drive, and you can find them in the middle of the hydraulic manifold. They handle the high-pressure hydraulic fluid that powers the motor. If you mix up which one is the flow and which one is the return, you’ll notice your final drive motor running in reverse of what it is supposed to.

Case Drain Ports (C1, C2)

The ports on either side are the case drain lines. These ports are used to return oil from the motor's internal housing to the hydraulic tank and are significantly smaller than the flow/return ports. The hydrauluc fluid from these lines operates under low pressure and is used to lubricate internal components, such as the piston shoes, swash plate, and motor shaft bearings. 

Note that some motors may have two case drain ports, with one port in use and the other remaining plugged. Always use the uppermost case drain port to ensure the final drive motor is constantly filled with hydraulic fluid and to prevent cavitation issues.

Also note that case drain lines can sometimes have an inline filter. Installing a new final drive motor is also a great time to change the case drain filter, if your machine has one. 

Finally, we cannot overstate the importance of having the case drain output flow unimpeded back to the reservoir. Dr. Drive suggests that before installing the case drain line to the final drive, blow some air through it so that it is connected to the reservoir. You should encounter little to no resistance and should see bubbles in the reservoir.

Brake Port

Some final drives have an integrated parking brake, which will have a separate brake port. It may be on the side or behind the main housing. The brake port is one of the smaller lines and should only be pressurized when the travel lever is in operation.

Dual-Speed or Multi-Speed Ports

Motors with multiple speeds will have an additional port for the dual-speed function. It is used to control the speed of the final drive motor and will usually be the smallest line of all. Fluid will only flow through the lines when it the final drive is in high-speed mode. This particular port may be on the back side of the final drive or between the case drain lines.

Comparing Different Final Drives

This port is often smaller and can be mistaken for a case drain port. It's critical to connect the correct hose to avoid damaging the motor. If you connect the 2-speed line to the case drain port, it will damage the hydraulics on your final drive motor and void the warranty on your final drive motor.

In this final drive, we can see the A and B ports are located in the center with the case drain lines on either side. This is the simplest configuration. Note the size difference between the case drain ports and the A and B ports.

This is another simple configuration with the A and B ports in the center, flanked by the significantly smaller case drain lines.

This final drive configuration is a little different. At the top is the brake line b, with a single case drain port C located between the A and B lines

Ports on Larger Machines

For machines with larger tonnage, please refer to the video below.

Conclusion

If you have any doubt whatsoever about which port is which, give us a call here at Texas Final Drive. We are more than happy to help you navigate your installation and avoid taking any actions that could void your warranty.