Craftsman 1/2 HP GARAGE DOOR OPENER 139.53978SRT - Manual (Page 8)

Assembly Section: Pages 8-11
To avoid installation difficulties, do not run the garage door opener until instructed to do so.
Assembly Step 1
Assemble the Rail & Install the Trolley
The front rail has a cut out “window" at the door end
(see illustration). The hole above this window is
larger on the top of the rail than on the bottom . A
sm aller hole 3-1/2“ away is dose to the rail edge.
The back rail has a sim ilar hoie dose to the edge,
about 4-3/4“ from the far end. A 3-piece rail uses
two back rails.
Preferred assem bly is to position the rails right
side up, with the sm all holes along the sam e
edge.
1. Remove the straight door arm and clevis pin
packaged inside the front rail and set aside for
Installation Step 12.
2. Align the rail sections on a flat surface exactly as
shown and slide the tapered ends into the larger
ones. Tabs along the side will lock into place.
3. Place the powerhead on packing material to
protect the cover, and rest the back end of the rail
on top. For convenience, put a support under the
front end of the rail.
4. As a temporary trolley stop, clamp a locking pliers
onto the rail, 8“ from the center of the idler pulley
hole, as shown,
5. Check to be sure there are 4 black plastic wear
pads inside the inner trolley. If they became loose
during shipping, check all packing material. Snap
them back into position as shown.
6. Connect the inner and outer trolleys as shown.
7. Slide the trolley assembly along the rail from the
back end to the locked pliers.
Front Rail
(TO DOOR)
Waar Pads