The Jacobs chuck is the mechanical device on the tip of the drill that fastens all drill bits and extensions in place. Jacobs drill chucks are commonly used in high-powered electric drills. When your Jacobs chuck breaks, repairing the chuck means replacing it with a new chuck. This requires that you partially dismantle the drill, which can void your drill's warranty if you cause damage to the drill while replacing the chuck.
Unplug your drill's power cord or remove the battery pack if your drill is cordless. Disable the drill's trigger by pressing the locking button above or near the trigger. Place the drill on a sturdy work surface.
Grasp the chuck and rotate it counterclockwise until the jaws are fully expanded.
Determine how the chuck is fastened to the drill's spindle. Most Jacobs chucks are fastened with a single screw. This will be either a Phillips screw on the bottom side of the chuck or an Allen screw inside the chuck. Since most Jacobs chucks use a left-handed screw, turn the screw clockwise until the screw is removed from its threaded hole.
Insert the hex wrench that came with your drill into the Jacobs chuck. Place the drill so the chuck is hanging off the side of your work table. Strike the wrench so the chuck rotates counterclockwise. This will knock the chuck loose from the drill's spindle. Remove the chuck from the drill.
Place the new Jacobs chuck onto your drill's spindle so the threads on the spindle align with the threads inside the chuck. Rotate the chuck clockwise until it is firmly fastened to the drill's spindle. Reattach the chuck's retaining screw and tighten by turning it counterclockwise.