Most John Deere lawnmowers have a drive belt that is used to power the power take-off (PTO) or the mower deck that is attached to the tractor. Over time, the drive belt can become loose, come off of the pulleys or no longer fit right. This will require you to adjust or tighten the drive belt on the tractor. You can adjust a John Deere drive belt by first determining how tightly the drive belt is sitting on the pulleys.
Park the lawn tractor on a flat surface and turn off the engine.
Take the drive belt off of the pulleys on the tractor and the mower deck.
Detach the mower deck from the tractor. You will need to pull out the cottar pins that support the front brackets of the mower deck and then use a socket wrench to remove the bolts on the back.
Pull out the mower deck from underneath the tractor.
Remove the foot plate that covers the top of the mower deck with a screwdriver (if applicable).
Measure the length of the belt tension spring with a tape measure. The length of the drive belt spring can vary depending on the type of mower deck you have. Refer to the owners manual of your tractor for the proper length of the belt tension spring.
Increase belt tension by turning the nuts on the spring mount clockwise with a wrench. Turning the nuts counterclockwise will decrease belt tension.
Place the foot plate back on the mower deck and reattach it with the screwdriver.
Reposition the mower deck back underneath the tractor. Using the socket wrench, secure the back of the mower deck with the bolts. Then place the cottar pins back into the brackets that hold up the front of the mower deck.
Place the drive belt back on the pulleys. Make sure the V-grooved part of the belt is going over the pulley.
Removing the mower deck will make adjusting the belt tension spring easier than when the mower deck is still attached.
Too much tension on the spring can cause the belt to not fit correctly. Forcing the belt to fit may damage the belt or the pulleys on the tractor.