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.
This John Deere uses traction drive belt part number M74747 which is 104.72 inch long x 0.5 inch wide, HA section 0.31 thick, 32 deg.;
38" Black Deck belt part number M125218; 95.75" long x 0.56" wide, Special section, 0.45 thick, 36 deg., Premium
46" Black Deck belt part number M119539; 137.48" long x 0.56" wide, Special section, 0.45 thick, 36 deg., Premium.
Overall view of STX38 Gear drive belt (#1). The transmission is at left, electric mower clutch at right.
Flat idler and v-idler pulleys in mid-section of the belt (#2). Engage the parking brake to provide slack in the belt.
The belt guide must be removed from the flat idler pulley. Note how the guide post fits into a hole on the idler arm (#3, blue). Remove belt from pulley.
The belt guide for the middle v-idler pulley must be removed. Note how the guide post fits into a bracket on the frame (#4, blue). Remove belt from pulley.
Disengage parking brake and remove parking brake latch eyebolt (#5, blue).
Both tie rods must be disconnected at the steering shaft (#6, red).
The belt goes between the guides (#7, red) and around the transmission pulley.
Remove the belt guide from the front v-idler pulley next to the engine pulley (#8, blue). Note that the belt goes inside the guide at #8, red.
The electric clutch must be disconnected and removed. When re-assembling it be sure to engage the anti-rotation bracket (#9, red). The belt will be fed between the belt guides (#9, blue) and around the engine pulley.
Closer view from the left side of front section of the belt (#10). Electric clutch is seen at left.
Deere parts diagram (#11).
Belt routing for 38 inch black deck (#12).