On newer Bobcat models that share a common brake circuit, we've been seeing a failure pattern that starts small but takes out both final drives. And it might be affecting you! Read on to learn what it does and how to diagnose it on your equipment.
One of the issues we’ve seen on certain newer Bobcat models that share a common brake circuit begins when an internal seal fails in one final drive motor and creates a significant amount of internal leakage. Even though the charge pump may still be producing adequate pressure, the failed seal creates a leak path that robs brake release pressure from the opposite-side final drive. Because that second drive isn't getting enough pressure to release its brakes fully, it ends up working against itself, dragging and eventually failing as well.
Symptoms
Let’s take a look at the symptoms of this Bobcat issue that lead to failure.
Early/Initial Symptoms
At this point, only one final drive is being affected.
- You find fluid leaking or weeping from one final drive housing, often visible on the ground under the machine
- One track moves noticeably slower or weaker than the other during
- Your machine is pulling or drifting to one side when driving straight
- You notice slight dragging or resistance on one side, especially at startup
Progressive Symptoms
These are the symptoms associated with the opposite side starving.
- Overall travel power is reduced, and your machine feels sluggish on both sides
- Brakes aren’t fully releasing, dragging, or the drive is "fighting itself" when trying to move
- You notice an increased effort or RPM when you need to get the machine moving
- Excessive heat is coming from one or both final drives after use
- You hear unusual noise, whining, or grinding from the drive motors under load
Late-Stage Symptoms
Over time, both final drives will be impacted.
- You notice a severe loss of power on both sides of your equipment
- Your machine is struggling just to climb grades or move under load
- The hydraulic fluid heats up, not just the final drives
- Your machine experiences a complete loss of travel function on one or both sides
- There is premature wear or total failure of both final drive motors, even though only one had the original leak
Symptoms that Get Misdiagnosed
These symptoms generally look like …
- Charge pump failure (since brake release pressure is low)
- Hydraulic pump or main pump issues
- A single bad final drive motor, when in reality the second one is failing as a secondary consequence
- General "loss of power" that gets blamed on the engine or hydraulic system broadly, rather than traced back to the seal
But those aren’t the right places to look.
The Correct Diagnoses
What looks like a final drive, brake, or charge pump problem (or two unrelated final drive failures) might just trace back to a single seal failure on one side. This leak is quietly starving the other final drive of the pressure it needs. And to make matters worse, this can happen even when one of the final drive motors has just been replaced.
Tracking Down the Problem
So here’s one way to track down the problem, and it involves looking at the case drain flow and brake release pressure.
Case Drain Flow Test
This test helps to establish the existence of a leaking seal.
- Disconnect the Case Drain Lines: Pull the case drain (return) lines off of both the left and right drive motors. Be sure to cap the fittings or lines that run back to the hydraulic reservoir to prevent fluid from making a huge mess when you start up your machine. And don’t forget that residual hydraulic pressure may still be present, so relieve the system pressure according to the service manual before disconnecting any hydraulic lines. And don’t forget to grab a couple of buckets!
- Start the Machine: Once the return lines are safely capped, start your machine to pressurize the system. Let it run a few minutes to reach its usual operating temperature.
- Observe the Oil Flow: Watch how much hydraulic fluid is exiting the case drains on the drive motors. A healthy final drive motor will drop a small, steady trickle (low case drain flow), while a blown seal will look like a heavy, continuous pour (or fill the bucket rapidly).
- Identify the Failed Seal: If you see a much higher flow pouring out of one of the motors, it means that the hydraulic fluid is blowing right past that motor’s internal seals.
Brake Release Pressure Test
This test proves cross-drive pressure robbing, not just that a leak exists.
- Check OEM specs for minimum brake release pressure on that motor.
- Locate the brake release port on both final drives.
- Gauge one side, test alone – record independent pressure.
- Test the brake pressure – measure brake release pressure according to the Bobcat service manual and compare readings while operating each drive individually and together.
- Compare to see if there is a significant drop when both are engaged (vs. tested alone) signals cross-robbing.
- Confirm with case drain flow testing on the suspect side to quantify the leak.
- Document readings before teardown for diagnosis and warranty support.
So here’s what we’re looking for: independent pressure is fine; pressure that drops when both drives run together is the tell. That's your seal failure robbing the opposite side.
Conclusion
You may spend hours chasing a charge pump or hydraulic pressure problem, and may be testing the wrong components. Our technicians have observed this failure pattern on multiple Bobcat machines with this hydraulic configuration. The actual root cause may be a single seal failure that’s quietly robbing pressure from the opposite side. If you suspect your equipment might be experiencing this, why don’t you give us a call? And if you’re in the market for a replacement final drive, check out the massive inventory in our Final Drive Shop.