How to Fix a Hydrostatic Lawnmower Transmission

A hydrostatic transmission, which utilizes hydraulic power, is a common feature on excavators, lawn tractors, forklifts, winch drive systems, heavy lift equipment, agricultural machinery and earth-moving equipment. Almost all lawn and garden vehicles can implement this system. It's vital to know how to fix a hydrostatic transmission if you own a lawnmower that has one.

A faulty transmission must be repaired.

Clean the Oil Cooler

Step 1

Start the lawnmower engine and allow it to run for a few minutes to warm the transmission oil. Stop the engine and set the parking brake to make it safe for you to work on the mower.

Step 2

Lift the driver's seat and secure it in the upright position. This is where you will find the transmission oil cooler; a key component to ensure the transmission runs smoothly.

Step 3

Use a clean rag to clean the the transmission oil cooler and remove any debris or dirt, which can clog the fins and cause the mower to malfunction. The cooler looks like a small radiator and consists of hundreds of thin fins.

Clean and Fill the Oil Tank

Step 4

Locate the transmission oil tank (behind the transmission oil cooler) and clean the area around the cap with a cloth. This guards against anything spoiling and contaminating the oil.

Step 5

Check the oil level by removing the cap and using the dipstick connected to the underside of the cap to measure oil levels. It's the same premise as a car: if the reading isn't within the indicated desired parameters, fill it up with oil.

Step 6

Use a funnel to fill the transmission oil tank. Generally you would use a 20W50 oil for this type of transmission; check with a dealer or the user manual for your specific model. Refilling the oil should take care of any issues with rough idling.


Step 7

Inspect the charge pump at the rear of the transmission pump for any fluid leaking from this vital artery of your transmission.

Step 8

Locate the source of the leak. These leaks or abrasions will severely affect the flow of vital fluids to the transmission.

Step 9

Improve the shifting performance of your hydrostatic lawnmower transmission by adding lubricating fluid to all parts of the linkage system. This is the system attaching the gear controls to the drive system.