The John Deere 318 mower deck (part number OMM79000) is a fully adjustable garden tractor attachment capable of handling heavy mowing jobs on smooth or uneven terrain. Apart from occasionally replacing the mower blades and drive belts, these components should give years of trouble-free service. Adjusting the mower deck height is a straightforward process that requires no special tools.
Things You'll Need
Inflate the tires to the correct pressure first thing in the morning while the tires are cold. Park the garden tractor on a level surface and adjust the cutting height to the midway position.
Remove the ignition key. Turn the mower blades to the crosswise position relative to the fore and aft orientation of the tractor. Measure the height from the tip of the right-hand blade to the ground with a steel measuring tape. Locate the lock or clamping nut on top of the left-hand J-shaped bolt. Turn the nut counterclockwise half a turn with a wrench to loosen it.
Turn the adjusting nut on the J-bolt clockwise to raise the left side of the mower deck and counterclockwise to lower it. Adjust until the tip height of the left blade matches the tip height of the right blade. Tighten the upper adjusting lock nut.
Check for equal tension on each of the two front draft rods by moving them from side to side. If one moves more freely than the other, undo the lock nut and tighten the adjusting nut until you've equalized the tension on both rods. Undo the other draft rod lock nut in preparation for fore and aft blade adjustment.
Turn the mower blades to the fore and aft position. Measure the tip height of both the front and rear facing blades; the tip of the front blade must be 1/4- to 3/8-inch lower than the tip of the rear blade. Turn the height adjusting nut on each draft rod equally in either direction to adjust as follows: clockwise to raise the tip of the front blade or counterclockwise to lower the tip of the front blade. Tighten both lock nuts after adjustment.