Things You'll Need
Nut driver set
Many homes with garages have automatic door openers. Locking the garage door when it is down is not necessary, since the opener keeps the door from being raised. Overhead garage doors that are not operated by an opener may have a lock cylinder keeping the door secure when it is down. When locked, the cylinder moves lock bars on the door's inside into slots in the sides of the doorjamb keeping it from being opened. Replacing a garage door lock cylinder may be necessary when it no longer functions correctly.
Locate the lock cylinder on the interior face of the door. Remove the nuts and bolts securing the lock bars to the cylinder with a wrench. Slide the bars slightly away from the cylinder towards the vertical sides of the doorframe. Place the nuts and bolts aside.
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Locate the two retaining screws on the lock cylinder's surface that secures the lock handle on the garage's exterior face. Note the placement of the small helper spring on one of the lock bars, as the looped end of the spring may be mounted under one of the screw heads.
Loosen and remove the two retaining screws with a nut driver. Pull the lock cylinder straight out from the door's interior face. Pull the lock handle straight out from the door's exterior face.
Insert the replacement lock's lock handle into the mounting hole in the door's exterior face with the keyhole facing the correct direction and the handle in a horizontal position.
Position the lock cylinder to the door's interior face. Ensure the square shaft from the lock handle is inserted in the square hole in the cylinder and that the mounting screw locations are aligned.
Thread the retaining screws through the mounting holes in the lock cylinder to the threaded holes on the lock handle's backside. Ensure the loop of the lock bar helper spring is replaced in its original position under one of the screw heads if applicable. Tighten the screws with a nut driver.
Slide the lock bars back towards the lock cylinder. Line up the holes in the ends of the bars with the holes in the tabs sticking out of the cylinder. Replace the nuts and bolts securing the bars to the cylinder and tighten them with a wrench.