the bit keeps falling out of my dewalt impact driver, the chuck feels loose. how do i fix it?

You're likely not inserting the bit correctly, or the quick-release chuck is worn. First, let's make sure you're installing it right.

1. Before you do anything, place the forward/reverse button in the lock-off (center) position or remove the battery pack.
2. Look at the chuck. It's a 1/4-inch hex quick-release type. It only accepts 1/4" (6.35 mm) hex accessories and 1" (25.4 mm) bit tips.
3. Take your bit and push it firmly straight into the chuck until you hear and feel a solid click. The bit should now be locked in.
4. To remove it, just grasp the bit and pull it firmly straight out.

If that didn't work and the bit still falls out, the internal hog ring (the retaining spring inside the chuck) may be worn or damaged. Do not disassemble the tool yourself. This requires service by a qualified repair person using identical replacement parts.

Heads up: Never modify the power tool or its chuck. Damage or personal injury could result.