Cordless Drill: Chuck Won't Hold Bits

The drill chuck supports the drill bits with jaws that firmly clamp on the bit. Over time, this part will wear down and lose its ability to clamp down firmly. Once this happens, you will need to replace the drill chuck.
To do this, start by inserting the proper screwdriver into the chuck to remove the screw at the bottom – also known as the chuck screw. Snug the chuck against the screwdriver and loosen by turning clockwise (this is reversed thread).
Once you’ve broken the tightness of the screw, loosen the chuck and continue to remove the screw. With the screw removed, insert a big allen key into the chuck and tighten firmly. Then, insert a pipe over the allen key for leverage and turn counter clockwise to loosen the chuck. You can also hit the allen key with hammer to loosen.
Once loosened, continue to remove from the spindle. Thread the new drill chuck on the spindle then insert the allen key back into the drill chuck and tighten the chuck onto the key. Insert the screwdriver inside the drill chuck to tighten the chuck screw, remembering that the screw is reversed thread.

The chuck screw is located inside the drill chuck, at the bottom, and helps securely support the drill chuck onto the drill. If this screw is not fastened down all of the way, it can prevent the drill chuck jaws from closing and locking onto the bit. Insert the proper screwdriver into the drill chuck and tighten this screw down. Remember it is reversed thread when tightening.

A worn key chuck or using the wrong size key chuck will cause this problem. Make sure you are using the correct key chuck, that is not worn.

If the ball bearings inside the chuck are worn, then the drill chuck will need to be replaced. Insert the proper screwdriver into the chuck to move the chuck screw at the bottom. Snug the chuck against the screwdriver and loosen by turning clockwise, remembering that the screw is reverse thread.
Once you have broken the tightness of the screw, loosen the chuck and remove the screw. With the screw now removed, insert a big allen key into the chuck and tighten firmly. Then insert a pipe over the allen key for leverage and turn counter clockwise to loosen the chuck or you can hit the end of the allen key with a hammer to loosen. Once loosened, continue to remove from the spindle. Thread the new drill chuck on the spindle and then insert the allen back onto the drill chuck. Tighten the chuck onto the key. Use the allen key to tighten the drill chuck onto the drill, then loosen the drill chuck and remove the allen key. Insert the screwdriver inside the drill chuck to tighten the chuck screw, remembering that this screw is reversed thread.