Did you know that a single leak, dripping one drop per second, can result in the loss of 420 gallons of oil annually? And that over 100 million gallons of fluids could be saved every year in North America if external leakage from hydraulic machinery and other lubricated equipment were eliminated.  And a small leak in your final drive is not just a nuisance—it’s an early warning sign of bigger trouble. Leaks mean critical fluids are seeping out, and damaging contaminants can make their way inside.

In this Shop Talk Blog post, we’ll discuss the causes of leaks, the symptoms to look out for, and why it's essential to address leaks as soon as possible.

Here are a few other Shop Talk Blog posts to take a look at:

• Maintaining Skid Steer Final Drives for Optimal Performance and Reliability​
• How to Check and Change the Gear Oil in a Final Drive Motor
• Advancements in Hydraulic Motor Design: Clearances
  
  

What Counts as a Final Drive Leak?

Not all leaks are created equal when it comes to final drives. The two types you may encounter are hydraulic fluid leaks and gear oil leaks; being able to distinguish between them can save you from costly damage. 

Hydraulic fluid leaks often stem from issues with the travel motor’s hydraulic connections, hoses, or seals. Gear oil leaks, on the other hand, typically point to problems within the planetary gear hub or its associated seals and bearings. Spotting the difference is critical: Hydraulic fluid is usually thinner and may appear amber or reddish, while gear oil is thicker, darker, and may have a strong sulfurous odor due to the presence of extreme pressure additives.

Common indicators include puddles forming under the machine, wet or oily residue collecting around the sprocket, and greasy buildup near the final drive’s drain plug or hub bolts. However, not every leak will leave an obvious trail. 

Some leaks only manifest under pressure, meaning fluid loss occurs during operation but leaves no visible puddle when your skid steer or mini excavator is parked. Others are slow seepages that mix with dirt and dust, forming a thick grime that hides the leak entirely. 

Such hidden leaks are why it is essential to conduct regular inspections, checking for subtle clues such as dampness, unusual noises, sluggish performance, or unexplained fluid loss. Even a small leak can lead to significant damage over time if left unnoticed.

Common Causes of Final Drive Leaks

Let’s review some of the most common causes of final drive motor leaks.

Worn or Damaged Seals

Seals are the first line of defense against leaks in a final drive, and they are also one of the most common failure points. Over time, seals naturally degrade due to heat, pressure, and constant exposure to hydraulic fluid or gear oil. Harsh working environments, such as dusty job sites, abrasive materials, or extreme temperature swings, accelerate this wear. Once a seal loses its flexibility or becomes damaged, it can no longer maintain a tight barrier, allowing fluid to escape. If not caught early, this can lead to accelerated wear of internal components or even catastrophic failure of the final drive.

Overfilled Gear Oil

Adding too much gear oil can create internal pressure within the planetary hub, especially as the oil heats up and expands during operation. This high pressure forces oil past the seals, causing leaks that might be mistaken for seal failure. In some cases, overfilling can even dislodge seals entirely. We recommend always following the manufacturer’s guidelines for oil levels and checking fill lines properly to help prevent this issue.

Shaft Wear or Scoring

The rotating shaft that passes through the seals must maintain a smooth surface for a proper seal. If the shaft becomes worn, grooved, or scored—often from abrasive contaminants or misalignment—it can damage the seal lip and create a path for fluid to leak. Shaft wear may also allow excessive movement or wobble, which puts additional stress on the seals and leads to premature failure.

Contamination

Dirt, grit, and other abrasive contaminants are major enemies of a sealed system. If contaminants manage to bypass external defenses, they can further damage seals from the inside, clog breather valves, and mix with fluids to form abrasive sludge. This not only increases the likelihood of leaks but can also degrade the lubricating properties of hydraulic fluid or gear oil, leading to broader system damage.

Installation Errors or Physical Stress

Incorrect installation is a common but often overlooked cause of final drive leaks. Using improper tools,  applying excessive force, or misaligning components during installation can cause seals to pinch or tear before the machine even starts. Physical stress, such as impact damage from a collision or operating your machine beyond its design limits, can also dislodge seals from their position or crack housing components, both of which may result in leaks. Ensuring proper installation and avoiding unnecessary mechanical shock are key to leak prevention.m

Why Final Drive Leaks Are a Big Deal

Final drive leaks are very problematic. First, they will lead to reduced lubrication and overheating if ignored long enough. Then, there’s the issue of contaminants entering through bad seals. This domino effect can lead to catastrophic damage, along with escalating repair costs and very expensive downtime. They should never be ignored.

If you’ve spotted signs of a final drive leak—or just want to make sure your equipment is running at peak performance—don’t wait until minor issues turn into major repairs. Contact the experts at Texas Final Drive for diagnostic support, replacement parts, or a quote on a remanufactured final drive. We’re here to help you keep your machines running smoothly and minimize downtime.