The John Deere STX38 riding lawnmower runs the dual mower blade deck pulleys with the main drive belt running from the pulley under the engine. This main drive belts not only runs the deck pulleys, but it also rotates the pulley above the mower deck that has a belt that runs the rear wheel pulley. The mower blades will stop spinning and the rider will stop driving when the drive belt snaps. With a few supplies you can change the drive belt on the John Deere STX38 right out on the lawn.
Turn off the mower. Raise the deck height handle to the highest setting.
Slide the blocks of wood under each side of the mower deck. Lower the deck height handle to the lowest setting. This will put slack in the drive belt.
Unscrew the four bolts that hold each shield over the two deck pulleys on top of the mower deck. Use the proper sized wrench to remove the bolts.
Pull the shields off. Pull the old belt off of the pulleys. Slip the new belt around each of the pulleys, V-side in.
Unscrew the three keeper pins screwed into rider frame around the pulley bolted to the base of the engine crankshaft --use the proper sized wrench to remove the keeper pins.
Slip the old belt out and slip the new belt around the pulley, V-side in. Tighten the keeper bolts back into the base of the rider frame around the crankshaft pulley.
Tighten the deck pulley shields back over the deck pulleys.
Raise the deck height handle to the top setting. Remove the blocks of wood.