Diagnosing a Final Drive Motor That is Screeching

Feb 20th 2021

It's definitely not a good sign when your final drive motor screams or screeches! One of our customers sent us this video, and we were able to make a diagnosis. Read on to learn more!

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

A Final Drive That Sounds Like It's Dying!

One of our customers sent us a video of what their final drive motor was doing to see if we could give them an idea of the problem before they sent it in. The footage is below ... And be prepared to hear some high-pitched squealing.

You'll notice it starts out with the sound of a smooth running engine in the background. As the drive motor starts to turn, it seems to almost hesitate, as if its trying to generate enough torque to overcome a substantial load. As it picks up speed, you can hear a grinding noise or low growl. As the speed increases, that low growl transitions into a high pitched-wail that stops as soon as the final drive stops. And it doesn't matter which way the drive is turning -- the same noises manifest in both forward and reverse.

Diagnosis

Our team was able to reach a conclusion from the video: weak charge pump that is preventing the brake on the final drive from fully releasing. Charge pumps are responsible for providing the necessary back pressure to keep the hydraulic system and certain components (like the breaks) operating correctly. When the charge pump is weak, it can't provide enough pressure to fully disengage the brake. That means that when the motor tries to turn, the brake discs drag (violently) across the splines in the brake housing. The dragging is what is responsible for the sound. \

In the picture above, you can see a comparison between good brake disc pack (left) and damaged brake discs (right). Notice the extreme discoloration and worn appearance of the interior and exterior teeth.The brake discs will eventually be destroyed, which isn't that expensive but the damage to the brake housing can be serious -- and the brake housing is much more expensive to replace. Below you can see a brake housing with seriously damaged splines, all due to a weak charge pump not releasing the brakes.

Complications from a Weak Charge Pump

If your final drive starts sounding like this, you should stop running it. The longer it runs, the worse the damage is going to be. As we already mentioned, you will damage the discs in the brake pack and start damaging the splines in the brake housing. As the teeth on the brake discs drag across the splines, slivers of metal will eventually come off. Those slivers contaminate the hydraulic fluid in your final drive. That leads to surface damage of other components in your drive motor. Even though the charge pump and braking system is replaced the life of other key components is reduced and the power and torque your final drive can generate will be reduced.

Conclusion

The root issue here is not the final drive motor, which means you can replace the drive motor with a brand new one and soon the very same problems will develop. That's why we emphasize taking the time to ensure that the problem isn't related to an external factor. If your final drive is making a similar to this one, don't keep running it! Most likely your issue is also a weak charge pump, but if you don't do anything about it it will eventually lead to a totaled final drive.