LiftMaster 3950 3950 Addendum Manual - Page 3

DEAD SHAFT REQUIREMENTS Dead Shaft Door Construction Drum 2nd Drum Spring Axle Door Bracket Door Guide Figure 4 - Dead Shaft Door Construction Spring Clearance The Model 3950 requires that the internal door springs do not interfere with the 4.5" mounting pattern on the end drum (Figure 4 ). Some door manufacturers require the door to be ordered with a modification (ex. Prep for Operator), so that an extra drum (Figure 4 - 2nd Drum) is added on the end of the door barrel to provide an unobstructed platform for door sprocket mounting. Inspect for interference by sliding the sprocket on the door shaft to drum and aligning with the 2.25" from center, 3 equally spaced hole pattern. Sprocket mounting holes should not be obstructed by the door spring for a minimum depth of 3". (Figure 6 - Bolt Clearance). See Figure 8 for Mounting Template. 3