If the belt broke on your John Deere X300 riding tractor, you can't use it as a mower until you replace the drive belt. This belt runs off a pulley system mounted to the underside of the motor and the top side of the mower deck. Installation is straightforward and just takes a basic wrench set to complete.
Park the X300 on level ground and lower the mower deck to its lowest position.
Disengage the mower deck via the PTO drive lever, if you have not already done so. To disengage the drive, push the lever down as far as it will go.
Lay on the ground in front of your X300 and locate the PTO drive pulley under the engine. Remove the bolts holding the belt cover over the pulley, using your wrench. Swing the cover out of the way.
Place the belt onto the pulley and stretch it back toward the mower deck.
Hold the belt into the V-groove on the pulley and reinstall the belt guard, which holds the belt in place for the remainder of the process.
Place the belt around the pulley system on the mower deck. Follow the belt routing diagram on the top side of the deck. If you install the belt incorrectly, the blades could crash into each other or spin backward. If the diagram is missing, refer to the diagram in your owner's manual.
Engage the PTO drive lever before you begin mowing your yard again.