Ariens Riding Mower Transmission Problems [Troubleshooting + Fixes]

Ariens riding lawn mowers have a hydrostatic transmission system that ensures efficient speed change. Like other transmission systems, hydrostatic transmission systems have mechanical components such as drive axles and metal hoses that cause mower operation problems whenever they develop defects. 

Proper diagnostics will help you fix Ariens riding mower transmission problems. Most problems will come from belt breakage, transmission pump failure, overheating, and loss of drive at high throttle. 

How do I know if my lawnmower transmission is bad?

The most surefire sign you have an issue with your lawn mower’s transmission is if you can’t get the mower to move either forward or in reverse. Zero movement forward is sometimes accompanied by jerky movements due to the failure to create enough transmission pressure. 

Ariens Riding Mower Transmission Problems Troubleshooting + Fixes

A more subtle sign of lawn mower transmission problems is the mower slowing down. This is commonly associated with old oil that no longer has the necessary hydraulic properties to facilitate transmission.

Sometimes, your Ariens mower moves normally while producing an irritating, high-pitched noise. This is usually a sign of bad transmission caused by a worn-out drive belt.

Finally, if you notice oil spills on the ground or a foul odor coming out of the engine while operating the mower, the transmission fluid may be leaking. The foul smell is due to the transmission oil leaking into the engine.

Note: White smoke might accompany the foul odor from a running engine when the hydraulic transmission oil leaks into the engine. 

What causes mower transmission problems?

The most common causes of mower transmission problems in hydrostatic transmission mowers include old hydraulic oil, cavitation, and a defective drive belt. Other less common causes include a faulty pressure sensor and hydraulic fluid leaks.

What causes mower transmission problems?

Bad hydraulic fluid

Hydrostatic mowers use hydraulic fluid to power the transmission process. Any hydraulic fluid left in the hydraulic system for too long goes bad, resulting in transmission failure.

Hydraulic oil contains an anti-foam additive that decays over time, resulting in the oil soaking up air and air moisture. Unlike fresh oil, such entrained hydraulic oil cannot deliver the pressure required for optimal transmission.

Note:  Entraining is the condition whereby air and moisture infuse into hydraulic oil.


Cavitation is a condition whereby the mower’s hydraulic system has air in it. It’s a common occurrence in lawnmowers left sitting idle all winter. The hydraulic pump cannot create adequate pressure to facilitate transmission with more air than oil running through the lines.

Damaged drive belt

Transmission failure in Ariens mowers can also be caused by the drive belt displaced from the drive system pulleys. A worn-out or broken drive belt will also cause transmission failure, and your mower won’t move in either direction.

Note: A common sign of a worn-out drive belt in an Ariens Zero Turn lawn mower is a squealing sound when the mower is running.

Defective pressure switch

Some lawnmower models come with a pressure switch as a security feature that prevents the mower from moving when no one is sitting on it. It works by sensing the weight pressure of the mower operator as soon as they’re seated. A broken or defective pressure switch might not detect when someone’s on the mower’s seat, keeping the mower from moving.

Leaking hydraulic fluid

Forward movement may also be hindered if your hydrostatic transmission mower leaks hydraulic fluid. This can be caused by cracks or wear within the hydraulic system, as explained below.

  • The rubber gasket seals can wear down over time. The resulting cracks lead to oil leaks.
  • The hydraulic oil lines can develop hairline cracks, resulting in slow leaks.
  • The crankcase gaskets can break or develop cracks due to constant pressure.

How to fix Ariens riding mower transmission problems?

To fix hydrostatic transmission problems in an Ariens riding mower, consider replacing the old hydraulic fluid, flushing air from the system, or installing a new pressure switch. Other possible fixes include replacing the damaged drive belt and sealing/replacing the source of the hydraulic fluid leakage.

Drain and replace the old hydraulic oil

  1. Position the mower on a level, flat surface to ensure that it drains properly. Place a drain pan underneath the oil drain plug to catch the hydraulic oil.
  2. Detach the drain plug by unscrewing it with a socket wrench. Let the mower stay in that position for several days until you’ve drained out all the old, entrained hydraulic fluid.
  3. Once all the old oil has drained, fill the reservoir with fresh hydrostatic transmission oil.
  4. Finally, clean the oil reservoir cap of dirt and debris to avoid contaminating the transmission system. Replace the cap and reattach the drain plug.
  5.  Starting the mower to check if the problem has been fixed.

Note: For optimal performance, it’s best to use a hydraulic oil brand that the brand manufacturer recommends.

Flush air out of the system

If your Ariens riding mower doesn’t move due to air inside the lines, fix the issue by flushing the air out. 

  1. Start by securing the mower in position using jack stands. You can also improvise a restraining blockade using wooden blocks. Meanwhile, ensure you’ve engaged the parking brake, too.
  2. Disengage the mower’s transmission as per the manufacturer’s manual. You can turn on the mower and place it in neutral mode before releasing the brakes. 
  3. Push the throttle forward for five seconds before pulling it to the reverse position for another five seconds.
  4. Repeat the forward-reverse cycle at least five times, as doing so helps to flush air out of the transmission system. 
  5. Power off the mower and re-engage the transmission. 
  6. Finally, start the mower and drive it forward and reverse to see if there are still any movement issues.

Replace the pressure sensor and drive belt

If the pressure sensor beneath the mower seat is faulty, you should install a new one. Ensure the replacement pressure switch is the same brand as the old one or is compatible with your mower. 

Alternatively, you can hire a mower technician to replace the pressure sensor for you at a fee. It will cost $45 on the lower end up to $250 on the higher end, depending on service complexity. 

Note: If the mower isn’t moving because of a worn-out or misplaced drive belt, replace the belt, too. 

Repair or replace leaking transmission system components

If the transmission issue is hydraulic fluid leakage, locate and seal the leaking part. Due to its complexity, it might be best to call in lawnmower repair experts. You’ll have to replace your leaking crankcase gaskets or gasket seals if the damage is extensive

Ariens riding mower transmission care and maintenance tips

Here are some tips to care for and maintain your Ariens mowers:

  • Change the transmission oil every 400 hours of running the mower.
  • Drain out the transmission fluid at the start of winter and replace it with new hydraulic fluid the following spring.
  • Call a professional lawnmower technician to run periodic diagnostics and give your Ariens mower a clean bill of health.

References Troubleshooting Mower Forward and Reverse

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