Here are four basic facts about gear oil that you should know (and you probably already do!). Let’s review them.

The Three Purposes of Oil

Oil serves three purposes: cooling, cleaning, and lubrication. That’s why oil contaminated with things like dirt, sand, and metal shavings can be so damaging to your final drive. Contaminated oil results in premature wear and tear of key components in your final drive, reduced ability to lubricate, and a greater tendency to overheat.

Why Gear Oil is Thick

Gear oil, also referred to as gear lube, is significantly thicker than hydraulic fluid. This is because a thicker film thickness is needed between the interacting surfaces inside the planetary hub. Gear oil can be thicker than hydraulic fluid, which also serves to lubricate and cool, because it doesn’t need to be pumped: the gears are basically bathed in the gear oil throughout their operation. By the way, when a final drive is leaking a thick oil from behind the sprocket, it indicates an issue with the face seal and the fluid that is leaking would be gear oil from the planetary hub.

Why Gear Oil Can Smell Hellish

Don’t be surprised if your gear oil smells like sulfur. Sulfur compounds are commonly used as high-pressure lubricants specifically for gears. These compounds bond to the surfaces of the gears (and other components) to prevent damaging metal-to-metal contact even under extreme forces and pressure.

Importance of Changing the Gear Oil

Did you know the useful life of your final drive is directly proportional to how often you change out the gear oil? The gear oil should be checked about every 100 hours of operation or once a month, and should be changed at least once a year. As you already known, oil isn’t like milk: there isn’t a simple expiration date that tells you when you need to change out the oil. The useful life of oil is determined by a variety of factors, including operating conditions and what type of contamination control you have in place. It will also begin to degrade chemically as it is exposed to heat (and air and water!). However, there are manufacturer’s guidelines to give you a good idea of how often you need to change the oil, and what oil you should be using.

Conclusion: Gear Oil Key Component

Gear oil is a key component in your final drive as it serves to cool, lubricate, and protect. Contamination and degradation can reduce the ability of gear oil to perform those tasks, making the useful life of your final drive proportional to how regular you are about changing out the gear oil.