the chuck on my m18 fuel hammer drill won't tighten all the way, bit just slips no matter what

Diagnosis

The issue with the Milwaukee M18 FUEL Hammer Drill 2904-20 typically stems from a failure in the internal ring-and-pinion mechanism of the all-metal ratcheting chuck. In these high-torque models, fine particulate matter—specifically concrete dust from masonry drilling or microscopic metal shavings from steel fabrication—migrates past the chuck sleeve and settles into the internal threads and the spring-loaded locking mechanism. When this debris accumulates, it creates a physical obstruction that prevents the jaws from closing completely around the shank of the drill bit. Because the 2904-20 uses a high-torque gear train, any slight slippage in the chuck causes the bit to spin rapidly within the jaws, which further polishes the metal surfaces of the jaws and the bit, reducing friction. If you hear a clicking sound but the jaws aren't tightening, the internal ratcheting pawls are likely fouled or have become misaligned due to excessive side-loading during a jammed hole. You can confirm this by attempting to tighten the chuck while it is empty; if it locks firmly without a bit but slips with one, the issue is likely debris-related or a worn jaw face.

How to Fix It

To restore the clamping force of your 2904-20 chuck, follow this deep-cleaning and lubrication sequence:

1. Remove the battery from the tool to ensure safety and prevent accidental trigger pulls during the process.
2. Open the chuck jaws to their maximum extension. Use a pair of needle-nose pliers to pull the jaws slightly outward if they feel sticky.
3. Using a high-pressure air compressor with a long-reach nozzle (or a can of compressed air with a straw), blow air directly into the center of the chuck. Angle the nozzle toward the rear of the jaws and rotate the chuck sleeve 360 degrees multiple times to clear debris from the internal threads.
4. Apply a small amount of electronic-grade contact cleaner or a non-residue degreaser into the jaw mechanism. Rotate the chuck open and closed several times to break up any hardened concrete slurry.
5. Once the debris is cleared, apply two drops of a high-quality, light machine oil (like 3-in-1 oil) or a dry PTFE lubricant into the jaw tracks. Avoid using heavy grease, as this will attract more dust and cause the same problem to recur.
6. Insert a standard 1/4-inch hex shank bit and tighten the chuck firmly by hand. If it still slips, use a chuck key or a pair of pliers to give the sleeve an extra quarter-turn of torque to seat the internal pins.

If That Didn't Work

• Check for Bit Deformation: Inspect the drill bit itself. If you are using a worn-down round-shank bit instead of a hex-shank bit, the 2904-20's jaws may not have enough surface area to grip. Switch to a high-quality impact-rated hex bit to see if the grip improves.
• Inspect for Internal Spring Failure: If the chuck feels "loose" or doesn't provide any resistance when tightening, the internal tension spring may have snapped. This requires a full replacement of the chuck assembly (Part # 45-20-xxxx series depending on the specific build date), as these units are not designed to be serviced internally.
• Address "Polished" Jaws: If the jaws are clean but the bit still slips, the internal gripping surfaces may be "glazed" from heat. Use a small piece of 400-grit sandpaper to lightly scuff the inside of the chuck jaws to restore the necessary friction.
• Verify Gearbox Alignment: In rare cases, a hard impact can bend the spindle slightly. Place the drill on a flat surface and rotate the chuck slowly; if you see a noticeable wobble (runout), the spindle is bent, and the chuck will never tighten squarely, necessitating a professional gearbox repair.

Heads Up

• Always wipe your drill bits clean of oil or grease before inserting them into the chuck; lubricated bits are the primary cause of slippage in the 2904-20.
• Avoid over-tightening the chuck with a wrench or pliers during normal use, as this can deform the internal ratcheting ring and lead to permanent slipping.
• When drilling into masonry, periodically blow out the chuck with air to prevent concrete dust from migrating into the mechanism.
• Ensure you are using the correct speed setting (1 or 2) for your application; using high speed for high-torque drilling can cause the bit to "snap" loose from the chuck more easily.