There are two types of adjustable down limit on Liftmaster garage openers: the travel distance limit setting and the downward force limit setting. Adjusting these dials alters how far the garage door travels while closing and how much force in kilograms the motor uses. Changes are necessary if the door reverses during closing, moves with too much force or strikes the ground and moves back to the top. Two dials on the side of the motor head regulate the down settings.
Place a stepladder beneath the motor head of the garage opener. The motor head is the box containing the lightbulbs mounted to the ceiling.
Locate the limit and force adjustment dials located on the back and sides of the unit. The exact position varies by model. The limit dials have an icon of an opening or closing garage door; the force dials have an upward or downward arrow containing the letters "KG."
Adjust the down limit dial first: turn it a full turn counter-clockwise to increase the amount of downward travel by two inches, and clockwise to reduce the amount of travel. The setting is correct when the door reaches the floor and stays closed without reversing.
Adjust the down force dial: turn it clockwise one number to increase force and counter-clockwise to reduce force. The door needs more force if it reverses without reaching the floor or if there is too much force. Each number adds or removes a kilogram of force.
Test the opener using the remote. You might need to make several adjustments before you find the right balance. The door should close steadily and remain on the ground without reversing.