Replacing a Makita drill chuck is the same as replacing most other brands of drill chucks. The key is getting the chuck to release from the spindle after removing a screw that secures the chuck. Once you remove the faulty chuck, take it to a Makita dealer or a home-improvement centre. Purchase a chuck that matches the old one for a good fit on your Makita drill.
Press the locking tab on each side of the battery, and pull the battery out of the Makita drill.
Twist the drill chuck counter-clockwise to open the chuck jaws. Look inside the middle of the chuck, and locate the screw that secures the chuck to the spindle.
Remove the chuck's securing screw with a Phillips-head screwdriver. You must turn the screw in a clockwise direction because the screw is a left-handed thread.
Insert the short end of a 1/4-inch or larger Allen wrench into the chuck, and tighten the chuck around the wrench as you would with a drill bit. Tighten the chuck around the Allen wrench, using the chuck key.
Lay the Makita drill on its side, with the long end of the Allen wrench pointing to the left. Strike the Allen wrench with a hammer to turn the drill chuck counter-clockwise. Twist the chuck off the spindle by hand.
Thread the new chuck onto the spindle, and open the chuck jaws fully. Secure the chuck to the spindle with the retaining screw. Turn the screw counter-clockwise to tighten. The chuck will seat itself the first time you use the drill.