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Repair a sagging gate. Repair a swollen gate. Repair a misaligned hinge post. Repair loose hinges.
Drill holes into two opposite corners of the gate's frame, such as the bottom left corner and the top right corner. The space between the holes should match the openings at the end of the turnbuckle's threaded rods. Screw the threaded rods of the turnbuckle onto the frame using the pre-drilled holes. Thread each rod into one end of the turnbuckle. Make sure that the slot for the screwdriver is facing you and not the gate. Insert the screwdriver into the slot and turn it until the gate frame is square. Remove the gate from the hinge post. Plane some wood from the latch-side of the gate. Seal and paint the planed area. Reattach the gate to the hinge post. Push the hinge post against the fence frame. Attach temporary wooden braces to hold the hinge post in place at both the top and the bottom. Attach an L-bracket to the top using a screwdriver. Secure one side to the back of the hinge post and the other side to the frame's exterior. Repeat with the bottom L-bracket. Remove the gate from the hinge post by pulling the pins out of the hinges. Set the gate aside. Unscrew the remaining sides of the hinges from the hinge post. Drill out the holes using a 1/4" bit. Insert short lengths of 1/4" dowel into the holes. Cut the dowels flush with the surface of the post. Drill pilot holes for the hinge screws into the dowels. Screw the hinges back onto the hinge post. Replace the gate and secure the hinge pins.