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 M118760 which is 97.84" long, 0.5" wide, HA section, 0.31" thick, 32 deg., Premium.
Models: DEERE STX38, STX46 (black deck); SABRE 1338G, 1538H, 1546G, 1638HS, 1646H; EUROPRO 1338GS, 1538HX, 1546GS, 1646HS.
The front end of the idler tensioning spring hooks to the frame behind the engine pulley (#1, blue).
The parking brake latch handle bolt (#2) must be removed to replace the drive belt. The front of the brake latch spring is at (#2, green).
Both tie rods (#3, blue) must be disconnected from the steering shaft arms. The parking brake latch handle bolt has been removed (#3, red). Bring the front loop of the belt over the parking brake latch and around the steering shaft (#3, yellow).
Loop the back end of the belt around the transmission pulley (#4).
Bring the front loop of the belt through the belt guides and around the engine pulley (#5). The front hook of the tensioning spring is at #5, red.
The back end of the idler tensioning spring hooks into a notch on the backside of the idler arm (#6, red). 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. The left-hand length of the belt runs directly from the engine pulley to the transmission pulley.
The rear hook of the brake latch spring is at #6, blue.
John Deere STX38 and STX46 Hydro drive belt diagram (black deck)(#7).