Left-hand and right-hand are referenced from the point of view of the tractor operator.
The flat backside of the belt rides on flat idlers; the inside vee rides in v-idlers and pulleys.
These John Deere products use belt part number M74747 which is 104.72" long, 0.5" wide, HA section, 0.31" thick, 32 deg.
Overall view of the drive belt layout (#1). The engine pulley is at the right and the transmission is off to the left.
The parking brake latch handle (#2, yellow) and its associated spring (#2, blue) must be removed to change the belt.
The front end of the brake latch spring (#3, blue) attaches to the brake latch handle bolt and the back end hooks to a bracket on the frame (#3, yellow).
Both steering tie rods must be disconnected (#4, blue) to loop the belt over the brake latch rod and around the steering shaft (#4, yellow).
Bring the front loop of the belt around the engine pulley and the v-idler next to it. Be sure the belt runs inside each of the belt guides (#5, blue). The front hook of the tensioning spring is at #5, yellow. The electric clutch locks into the post at #5, red to prevent the clutch from rotating.
Loop the back end of the belt through the belt guides and around the transmission pulley (#6).
The back end of the idler tensioning spring hooks into a notch on the backside of the idler arm (#7, red). Both belt guides must be removed. Set the parking brake to provide slack in the belt. Route the belt around the idlers; the flat backside of the belt rides on the flat idler; the belt vee rides in the v-idler. Note where the belt guides set into a hole in the idler arm (#7, blue) and a bracket on the frame (#7, yellow). The back end of the brake latch spring can be seen at #7, green.
A notch on the electric clutch fits around the post extending from the engine pulley guide (#8, yellow) to prevent the clutch from spinning.
Deere STX30 and STX38 diagram (#9).
John Deere STX38 yellow deck (#10).