I show how a hydrostatic transmission drive unit works on a John Deere 2320 HST compact utility tractor. This unit had a drive-shaft u-joint failure which broke the input shaft to the hydrostatic drive transmission.

The hydrostatic drive is divided into two portions, a variable flow pump controlled by a swash plate, and a fixed ratio hydraulic drive motor.

The forward / reverse speed of the tractor is controlled by foot pedals, which are connected by linkage to the swash plate in the drive pump. This controls the direction and flow rate of hydraulic fluid sent to the hydraulic drive motor.

The hydraulic drive motor is forced to turn in either direction based on the flow rate and direction of the hydraulic fluid. The motor will also hydro-lock on the fluid when there is no flow, causing the drive motor to also work as a brake.

If you have one of these JD 2320 tractors, be sure to check your driveshaft u-joints and keep them greased!