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Zero Turn hydrostatic transmission problems and solutions

Zero Turn mowers use hydrostatic transmissions to move the wheels. The hydrostatic transmission transfers power from the mower’s engines to the hydraulic pumps.

The pumps then use liquid pressure to move the wheels. This eliminates the need for gears and ensures better speed changes.

Although these machines are efficient, Zero Turn mowers suffer from hydrostatic transmission problems. These issues can cause the mower to fail to move forward, backward, right, left, or move at all.

The first indication that your Zero Turn mower has a hydrostatic transmission issue is when it is not moving forward, backward, right, or left.

Other indicators include an oil leak and difficulty in shifting the mower.

In other cases, the mower does not produce enough power to cut your lawn, and the wheels continue moving even when the mower is in the neutral position.

What are the solutions to common hydrostatic transmission problems?

Zero Turn mower

1. Check the condition of the drive belt

Zero Turn mowers with a hydrostatic transmission have a drive belt. The drive belt works by transferring the radial torque of the engine shaft to the input shaft of the transmission.

It propels the machine to move forward and spin the blade. However, a worn, loose, or broken drive belt can affect the movement of the mower.

Therefore, inspect the drive belt to ensure it works properly or is well positioned on the pulleys. If you see any signs of wear and tear, replace it.

2. Purge the hydrostatic transmission

Perhaps the most significant factor that causes issues with the hydrostatic transmission is air in the hydraulic system.

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Air in the system can subsequently lead to system failure. The reason is that Zero Turn mowers have a hydraulic pump that is not designed to pump air.

When air enters the system, it becomes compressed air and generates heat. As a result, it contaminates the hydraulic fluid, and foaming can occur.

As the fluid gets degraded, it damages the system’s internal components, resulting in loss of lubrication, overheating, and burning of seals.

The best way to fix this issue is to purge a hydrostatic transmission. The purging process may be different depending on your machine.

However, here is a general guide.

  • Check the oil level.
  • Place the mower’s drive axle on jack stands with wheels off the floor.
  • Start the engine and run it at an idle speed.
  • Move the throttle control to the SLOW position.
  • Put the control levers in the NEUTRAL position.
  • Disengage the clutch or brake pedals slowly.
  • Move the motion control levers to the FORWARD position.
  • Hold for at least five seconds.
  • Move the levers to the REVERSE position.
  • Hold for at least five seconds.

At this point, repeat the procedure twice. Then:

  • Move the motion control levers to the NEUTRAL position.
  • Shut off the engine.
  • Engage the parking brake.
  • Check the oil level and add it as required.
  • Placing freewheel control into the driving position to engage the transmission.
  • You can also close the bypass valves on the pumps to engage the transmission.
  • Sit in the operator’s seat to start the engine.
  • Move the throttle control to full speed once the engine runs.
  • Slowly disengage the clutch or brake pedal while the motion control levers are in the NEUTRAL position.
  • Move the motion control levers forward.
  • Once the machine moves a few feet forward, slowly move the control levers to the REVERSE position.
  • Move the motion control levers to the NEUTRAL position after the mower moves forward.
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At this point, you have purged your mower’s hydraulic system. However, you must repeat the procedure at least three times for maximum purging.

3. Change the hydraulic oil

When you notice that your Zero Turn mower is weak on one side or experiences sluggish operation, the culprit is often old or overused fluids.

The solution is to change the hydraulic oil from the oil reservoir. But, first, you must drain the oil thoroughly to avoid future problems.

Here is what to do:

  • First, position the mower on a flat, level surface.
  • Remove the drain plug.
  • Allow the mower to stand in the same position for several days until the last drop of oil drips.

Changing the oil two hours after the first operation for a new Zero Turn mower is crucial. Also, it is helpful to check the oil level all the time.

The best time to check the transmission fluid is every 200 service hours. In that case, you will have to add more oil or change it if necessary.

But you must follow the manufacturer’s instructions on changing or servicing your mower.

Zero Turn mower

4. Inspect the mower

You can correct many hydrostatic transmission issues by constantly inspecting your mower. Some of the things to inspect are:

  • Check the oil level and add some if needed. Beware of any oil leaks.
  • Check the connections and hoses or gaskets for damage or leaks.
  • Finally, check the pump cooling fins for any damage.
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You should also consider cleaning the pump cooling fins using compressed air.

Can you damage a hydrostatic transmission?

It is easy to damage a hydrostatic transmission of a zero-turn mower. Generally, these machines have a fluid that drives the transmissions to allow for easy steering by altering the fluid flow to the wheels.

Since the mower has two levers, pushing or pulling the handles slows down or increases the mower’s speed to the left or right wheels.

As a result, the mower turns in your preferred direction. However, if the machine has a hydrostatic transmission, pushing it too hard causes the fluid to move backward via the pump.

That action can damage the seals. The right thing to do is disconnect the drive before moving the machine.


You can fix a weak hydrostatic transmission based on the issue at hand.

If the mower cannot move forward, backward, right, or left, check the drive belt for any signs of damage.

Also, consider purging the machine to remove air from the hydraulic system. Another step you can take is to change the hydraulic oil to fix a sluggish operation.