LiftMaster 3840 3840 Manual - Page 6

ASSEMBLY STEP 1 Fasten the Rail to the Motor Unit To avoid installation difficulties, do not run the garage door opener until instructed to do so. To aid in assembly and installation, replace the foam packing around the motor unit. Remove it after Installation Step 5. • Working on a level surface, align the rail assembly with the motor unit, as shown. • Slip the coupling over the rail sprocket. • Slide the rail through the motor unit bracket until the coupling fits securely over the motor unit sprocket. • Align the two bolt holes in the rail with those in the motor unit bracket. Insert four 1/4"-20x7/16" hex bolts. Tighten securely with a 3/8" socket wrench. • Turn release arm down to disengage trolley. • Slide the trolley onto and along the bottom of the rail. Align trolley with rack and turn release arm up to re-engage trolley. Be certain to install it facing correctly: the trolley release arm must be horizontal (lock position), with its arrow pointed away from the motor unit. HARDWARE SHOWN ACTUAL SIZE Hex Bolt 1/4"-20x7/16" Hex Bolts 1/4-20x7/16" Motor Unit Bracket Motor Unit Sprocket Rail Assembly Coupling Rail Sprocket Foam Packaging Hex Bolts 1/4"-20x7/16" Release arm Trolley Rack To motor unit 6