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Why Final Drive Leaks Are a Big Deal

Why Final Drive Leaks Are a Big Deal

Posted by Jim Strong on Feb 7th 2021

Leaks should never be ignored -- especially when it involves your final drive motors.

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Let's face facts: leaks coming from your final drives are often seen as an annoyance, but when they are ignored the result will be compromised motor performance and some costly repairs.

Final Drive Seal Failures

The vast majority of leaks are caused by a seal that is failing. Seals are responsible for two things: keeping something in and keeping other outs. On the hydraulic side of your final drive motor, seals keep the hydraulic fluid inside while keeping dust, sand, and other contaminants away from the hydraulic fluid. On the planetary side of your final drive, seals keep the gear oil inside so that it can lubricate the gear system while protecting the components from damaging contaminants. 

Aftermath of Final Drive Motor Seal Failure

A leak on the hydraulic side means hydraulic fluid is leaking out, which is never good. While it would take a serious leak on your final drive to significantly deplete fluid levels in your machine, it can happen. But is more worrisome, however, is the impact of contaminants that make their way into the hydraulic hub. Abrasive contaminants will accelerate the wear experienced by components and systems such as the rotator group in a axial piston hydraulic motor or the cam in a radial piston motor. 

In the image above, you can see a damaged cam ring from a radial piston motor where evidence of excessive wear can be clearly seen. This most often results from contamination making its way into the hydraulic fluid. While filters can catch abrasive particles before they make their way into regions in your hydraulic system, they can't undo the damage caused when these particles get caught between contact surfaces under high forces and pressures.

The performance of your final drive motor will suffer with this type of damage. And if your piston shoes are scarred up like this, let's just say that its a really bad sign! However, even relatively minor scratches will eventually impact the performance of your final drive motor.

Identifying the Source of a Leak

If you have a thick fluid dripping on the tracks or behind the sprocket, then your leak is gear oil coming from the gear hub. More specifically, if the drive is leaking near where the sprocket is mounted, then the mechanical face seal (also called a duo-cone seal or floating face seal) is going to be the problem. On the other hand, if you are seeing a significant amount of fluid that has a consistency similar to brake fluid, the leak is on the hydraulics side of your final drive motor.  


If you see the signs of a leak, then you need to get the seals involved replaced as soon as possible. Not only can important fluids leak out, but the components inside your final drive will be damaged.  Just think about the type of dust, dirt, sand, mud, and other debris your machine traverses on a daily basis and imagine having it inside your drive motor


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