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Final Drive Gear Oil: FAQs

Final Drive Gear Oil: FAQs

Posted by Jim Strong on Jan 19th 2022

We believe that answers to the following six questions about gear oil are essential to the performance and lifespan of your final drive motors.

Here are a few other Shop Talk Blog posts you might find helpful:

What Does Gear Oil Do?

Gear oil serves three purposes in the planetary hub of your final drive motor:

  • First, it provides lubrication for the gears and bearings
  • Second, it protects contacting surfaces (i.e., shafts and bearings, gear teeth) to prevent unnecessary wear
  • Third, it helps to conduct heat away from critical components in your final drive

How Often Should I Check Gear Oil Levels in a Final Drive?

Gear oil levels should be checked about every 100 hours of operation. If the levels are low, you can top it off, but you likely have a leak if you see consistently low levels. That means a seal is failing, and you need to get the main seal replaced. Failure to do so means your final drive gear hub is going to fill up with debris (e.g., sand, grit, dirt) while the lubrication leaks out.

Is a Gear Oil Leak Serious?

Gear oil leaks are serious. If you see the presence of a fluid that is thicker than hydraulic fluid and, on a tracked machine, it’s dripping onto the tracks, then you do indeed have a gear oil leak from a failed seal. Another way to tell if it is a gear oil leak or a hydraulic fluid leak is to consider how much has leaked out. Gear oil is typically limited to about 2 quarts, so excessive fluid points to a leak on the hydraulic side.

A leaking seal means that the planetary hub (gear hub) on your drive motor can run out of lubrication, which speeds up the natural rate of wear and can destroy your final drive if ignored. And if gear oil can leak out of the planetary hub, then other things can make their way into it. This includes water, dust, sand, dirt, and organic matter like crushed leaves. None of these are going to be good for your final drive. If your motor starts making grinding sounds or completely locks up, then the source is likely a gear oil leak.

Can Gear Oil Go Bad?

Gear oil can go bad--the process is called aging--and gear oil can age faster when your final drive motor runs hot. When gear oil ages, here’s what will happen:

  • It becomes thicker and less able to provide coverage for the components in your planetary hub
  • It doesn’t provide as much lubrication, which means higher friction and more heat generation
  • It can’t conduct heat as well
  • Essential additives, such as EP (Extreme Pressure) and AW (Anti-Wear) become depleted

This is precisely why it needs to be periodically replaced. And usually, one whiff of the gear oil in your final drive can tell our technicians if you’ve been replacing it often enough.

How Often Should I Replace the Gear Oil in a Final Drive?

You should replace the gear oil in a final drive motor at least once a year. Keep in mind that gear oil will age, especially if it’s exposed to heat. Aging gear oil loses its ability to lubricate the planetary hub’s gears, shafts, and bearings. In addition, additives like EP (Extreme Pressure) will degrade as well. If you check the gear oil levels in your final drive and it smells terrible, or the oil is extremely thick, you are overdue for a gear oil change.

What Kind of Gear Oil Works Best on for the Noted Drive Motors?

For a typical final drive motor, we recommend an 80W/90 oil with a viscosity around 120 centistokes at an operating temperature of 100°F (38°C).

For the average radial piston (Rexroth MCR style drives for example T series Bobcat) we suggest using the proprietary oil blend suggested by the dealer and manufacturer.

Also note that Final Drive Parts now carries our own gear oil: Ultra Performance Gear Lubricant, blended with additives to enhance its performance and its lubricative properties.

WFP Gear Lubricant comes in two different types:

  • A 32 oz. bottle engineered for planetary gearboxes
  • A 4 oz. bottle engineered for use with radial piston motors (like the Bobcat T190 or Bobcat T300)


At Final Drive Parts, we want to help you make your final drive motors last as long as possible. That’s why we dwell so much on topics like gear oil: we know from experience that gear oil can either extend the life of your final drive or, if neglected, total it. If you have any questions, give us a call at 877-330-7477!


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