December 7, 2017
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3 Gear Oil Myths Dispelled

When you’ve been repairing and rebuilding final drives for as long as we have, you see some pretty disturbing things.  In this week’s Shop Talk Blog post, we are going to dispel three major gear oil myths that we’ve encountered repeatedly:  gear oil doesn’t need to be changed very often, grease is a good temporary solution to leaks, and it’s all right to put off addressing leaks.  As you will learn, each one of these myths can destroy your final drive!

Myth #1: You don’t really need to change gear oil very often.

You know what happens when you don’t change the gear oil?  You end up with a planetary hub full of a thick, dark, smelly, useless goop with the consistency of pudding.  That revolting sludge is the result of gear oil breaking down chemically as it degrades with time, and it’s usually mixed with some contamination, too.  Gear oil has a limited useful life, and needs to be changed according to manufacturer guidelines.


Myth #2: A great solution to leaks is to use grease instead of gear oil.

Never use grease in the place of gear oil.  We’ve opened up final drives and, to our horror, found the gear hub full of grease.  Gear oil is thick, but it still flows like a fluid.   That allows the components in the planetary hub to be bathed in lubricant while the final drive motor is running.  Grease, on the other hand, doesn’t flow like a fluid — in fact, it really doesn’t go anywhere compared to gear oil, which means that all the components inside the gear hub aren’t going to be lubricated during operation.  That is obviously a very bad thing.  To make matters worse, the grease doesn’t carry heat away like gear oil, and it isn’t rated for high pressure applications.  In short, if you want to really destroy your final drive motor, use grease instead of gear oil.

Myth#3: Leaks can wait — just keep topping off the gear oil.

Leaks can’t wait.  Sure, you can keep topping it off with gear oil until a convenient time comes along to get that failed seal fixed — but in the meantime, not only is fluid leaking out, but abrasive particles (think dirt and sand, for starters) and water are making their way inside your planetary hub.  That is a recipe for disaster, and before long, not only do you have to pay to have the seals replaced, but you also have to add in an expensive repair for all the other damage that has occurred in the meantime.  Get those seals replaced ASAP!


Our Advice

Check and change the gear oil on a regular basis. Ideally, you should check the oil level about once every 100 hours of operation, and change the oil out at least once a year.  Use gear oil — never grease — in the planetary hub.  And, finally, when your final drive starts to leak, get those seals replaced as soon as possible, because the longer you wait, the more expensive the repairs are going to be.

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