After mowing with a John Deere lawn tractor, your yard should not look wavy nor scalped in places. Nor should it have an uneven, stair-step appearance. If any of these maladies appear, that could mean the mower deck is out of balance. You have two options to level the mower deck: side-to-side or front-to-rear. Whichever approach you take, levelling the deck should not take longer than 20 minutes to complete.
Park the machine on level, firm ground. Pull the sparkplug wire to keep the mower from accidentally starting while you are servicing the deck. Wear work gloves to protect your hands from cuts while working near the blades. Check that the tires have the appropriate amount of air in them. Set the cutting height at 2 inches, then put the mower in its cutting position.
Position both blades so they are parallel with the axles before performing a side-to-side deck adjustment. Use a levelling gauge to measure the outer tips of each blade. Twist the lift links nuts on the both sides of the mower clockwise to increase the height of the mower's deck. Turn counterclockwise to reduce the mower's height.
Position the right blade perpendicular to the axles to begin a front-to-rear deck adjustment. Use a levelling gauge to measure both blade tips to the ground. Consult your owner's manual to determine the acceptable difference between the front and rear tips of the blade; the measurement varies by the type of John Deere mower.
Locate the front lift rod, and loosen the rear nut. Raise the front of the mower by turning the front nut on each side of the lift rod clockwise. Lower the front of the mower by turning the front nut on each side of the lift rod counterclockwise. After you make the necessary adjustment, twist the rear nuts until snug.
Determine whether the deck is level by measuring the blade tips again after you have made whichever deck adjustment is necessary.
John Deere sells an inexpensive levelling gauge at dealerships.