my m18 fuel hammer drill just makes a clicking noise and won’t spin, battery is fully charged.

Diagnosis

The clicking noise you are hearing in the Milwaukee M18 FUEL 2904-20 is typically not a mechanical failure of the motor, but rather the sound of the electronic trigger and motor controller attempting to engage the brushless motor while a safety or mechanical fault is present. In this specific model, the clicking often indicates that the tool's logic board is detecting an "overload" or "stall" condition, triggering the electronic clutch to rapidly cycle on and off to prevent the windings from burning out. This most frequently occurs when the internal planetary gears have become jammed by metal shavings or debris, or when the chuck has become "seized" internally. Because this is a hammer drill, the hammering mechanism adds another layer of complexity; if the percussion sleeve is misaligned or jammed, the motor cannot complete the initial rotation required to engage the drive, resulting in a rhythmic clicking sound as the controller tries and fails to initiate the spin. You can confirm this by attempting to rotate the chuck by hand with the battery removed; if there is significant resistance or a "gritty" feeling, the issue is mechanical blockage rather than an electrical failure.

How to Fix It

To resolve a seized or clicking M18 FUEL Hammer Drill, follow these precise steps to clear the drivetrain and reset the controller:

1. Remove the M18 battery pack immediately to ensure the tool cannot accidentally engage during the process.
2. Grasp the chuck firmly and attempt to rotate it manually in both clockwise and counter-clockwise directions. If it is locked, do not force it with a wrench, as this can bend the internal spindle.
3. Use a can of compressed air or an air compressor with a nozzle to blow out the area where the chuck meets the gear housing. This clears any metal shards or construction dust that may be jamming the electronic clutch.
4. Set the mode selector ring to the "Drill" icon (disabling hammer mode) and the torque collar to the highest numerical setting. This bypasses the clutch's lower-torque restrictions.
5. Reinsert the battery and apply a "feathering" technique to the trigger—pressing it very lightly and releasing it rapidly several times. This can sometimes "kick" the motor past a dead spot or clear a software glitch in the controller.
6. If the tool begins to spin, run it on the lowest speed setting for 30 seconds to redistribute the factory grease across the planetary gears.

If That Didn't Work

• Inspect the Battery Terminals: Check the copper contact rails inside the battery slot for carbon buildup or debris. If the tool isn't getting a clean voltage spike, the controller may click but fail to provide enough current to overcome the initial inertia of the gears. Clean the contacts with a cotton swab dipped in 90% isopropyl alcohol.
• Check for Chuck Seizure: If the chuck is locked tight and won't move manually, the internal jaw mechanism has likely collapsed. You will need to remove the chuck by unscrewing the spindle bolt (usually requires a punch and hammer to break the factory seal) to see if the spindle itself is rotating. If the spindle rotates but the chuck doesn't, replace the chuck assembly.
• Test with a Different Battery: Even if the battery shows "full" on the fuel gauge, a single dead cell inside the pack can cause a voltage drop the moment the motor draws current. This causes the tool to "brown out" and click. Test with a High Output (HO) or Forge battery to ensure maximum current delivery.
• Internal Gearbox Failure: If the tool continues to click and the chuck is free-spinning, the planetary gear set may have a sheared tooth. This requires a complete teardown of the gear housing to inspect the hardened steel gears for fractures.

Heads Up

• Avoid using the "Hammer" setting when drilling into soft materials or using standard twist bits; this puts unnecessary stress on the percussion sleeve and can lead to the clicking stall condition.
• Periodically blow out the motor vents with compressed air. The brushless motors in the 2904-20 are powerful, but accumulated drywall dust can insulate the electronics, leading to premature thermal shutdown.
• Never force the tool to "break through" a jam by squeezing the trigger harder; the electronic clutch is designed to protect the motor, and forcing it can permanently damage the MOSFETs on the control board.
• Store the tool in a dry environment. Moisture in the trigger assembly can cause the electronic switch to intermittently fail, mimicking a mechanical jam.