A hydrostatic transmission uses pressure plates to allow energy to flow from the engine to the transmission. The transmission does not use gearing such as an automotive transmission. When you press the gas pedal, the RPMs of the engine engage the transmission and make the mower go. When you press the brake, the transmission disengages. This prevents the need to change gears manually. Although the transmission differs from an automotive transmission in many regards, you must still service the transmission to keep it in working order.
Clean Cooler and Check Oil Levels
Run the mower for a period of five minutes to warm up the transmission oil. Once warmed, stop the engine and set the parking brake.
Lift up and secure the driver's seat in the open position. In most cases, the transmission oil cooler for the transmission is located under the seat.
Locate the oil cooler behind the transmission oil tank. The cooler looks like a small radiator and consists of hundreds of thin fins. Wipe the fins down with a clean rag to remove debris.
Locate the fill cap on the transmission oil tank and clean the area around it with a clean rag. This prevents dirt from getting into the transmission oil tank.
Remove the lid and check the level of oil on the dipstick connected to the underside of the lid. If the dipstick indicates the oil level is low, place a funnel into the hole and fill the transmission oil tank to the appropriate oil level. In most cases, use a 20W50 oil. However, this could differ depending on the brand of mower. Check the owner's manual for the exact viscosity.
Change Transmission Oil
Lift up and secure the driver's seat in the open position.
Locate the silver or gray oil filter next to the transmission oil tank. Turn the filter counterclockwise with your hand to remove it from the coupler. If necessary, use an oil filter wrench to remove the filter.
Locate the inlet hose secured to the back of the filter coupler and pull it off. Drain the transmission oil into a large container. Plug the hose back in once oil stops draining.
Place an oil filter seal onto the oil filter, and place a small amount of oil onto the seal. Thread the seal onto the coupler and tighten it with your hand.
Wipe the area around the filler cap on the oil tank clean with a rag and then remove the cap.
Place a funnel into the transmission oil tank and fill it with 20W50 oil until the level of fluid reaches the "full" line on the oil dipstick.