the pad on my sander won't stop spinning, it just freewheels even when i'm not sanding and it's driving me nuts

Diagnosis

The issue you are experiencing is a failure of the electronic brake system integrated into the DCW210B motor controller. Unlike a standard orbital sander that relies on friction to stop, this 20V Max model uses a dynamic braking circuit that reverses the magnetic field of the motor the instant the trigger is released. When the pad "freewheels," it means the motor is not receiving the braking pulse, or the mechanical components are too obstructed for the brake to effectively halt the rotation. This typically happens because of "dust packing." Fine sawdust—especially from hardwoods or MDF—migrates through the ventilation slats and settles into the spindle bearings and the trigger assembly. If the trigger switch is physically obstructed by a grain of sawdust, it may not fully return to the "off" position, preventing the braking circuit from engaging. Alternatively, if the internal bearings are clogged with grit, the friction is reduced to the point where the electronic brake cannot overcome the momentum of the rotating pad assembly, leading to that annoying over-spin.

How to Fix It

To resolve this, you need to perform a deep clean of the drive assembly and the trigger mechanism. Follow these steps precisely:

1. Remove the 20V Max battery immediately to ensure there is no power to the motor during the cleaning process.
2. Unscrew the sanding pad using a coin or a flat-head screwdriver in the center slot. Remove the pad and the hook-and-loop backing plate entirely to expose the drive spindle.
3. Using a high-pressure compressed air nozzle (set to roughly 90-120 PSI), blow air directly into the spindle housing. Rotate the spindle by hand while blowing to ensure you are clearing debris from all sides of the bearing race.
4. Direct the air nozzle into the gaps around the trigger switch. Rapidly pull and release the trigger 20-30 times while blowing air into the switch housing to dislodge any trapped particulates that might be preventing the switch from clicking fully back into the "off" state.
5. Inspect the spindle shaft for any gummy residue (common when sanding resins or oils). If found, clean the shaft with a small amount of isopropyl alcohol on a lint-free cloth.
6. Reinstall the backing plate and pad, ensuring they are snug but not over-tightened, as excessive torque on the spindle can actually interfere with the braking speed.
7. Reinsert the battery and test the trigger response.

If That Didn't Work

• Check for Bearing Failure: With the pad removed, spin the spindle by hand. If you feel a "gritty" sensation or hear a metallic rattling, the internal bearings have failed. This prevents the electronic brake from grabbing the motor effectively. In this case, the motor assembly must be replaced as the bearings are pressed into the housing and not user-serviceable.
• Inspect the Trigger Spring: If the trigger feels "mushy" and doesn't snap back instantly, the internal return spring may have snapped or become displaced. This keeps the motor in a low-voltage state that bypasses the braking circuit. You will need to disassemble the outer plastic housing to inspect the spring tension.
• Test with a Different Battery: While rare, a battery with a failing cell or an unstable voltage output can occasionally cause the electronic controller to behave erratically, failing to trigger the braking pulse. Swap to a fully charged, genuine DeWalt 20V Max battery to rule out power delivery issues.
• Verify Pad Weight: If you are using a heavy-duty, non-standard third-party backing plate, the increased centrifugal mass may be overcoming the brake's capacity. Revert to the original DeWalt OEM pad to see if the braking returns to normal.

Heads Up

• Dust Extraction is Mandatory: The DCW210B is highly susceptible to internal dust buildup. Always use a vacuum attachment; letting dust fly freely into the air increases the risk of the brake failing again.
• Avoid Lubricants: Never spray WD-40 or silicone lubricant into the spindle or trigger area. This creates a "sludge" when mixed with sawdust, which will permanently seize the brake mechanism.
• Battery Safety: Always remove the battery before performing any cleaning or disassembly to avoid accidental trigger activation, which can cause the sander to "jump" and cause injury.
• Sanding Pressure: Avoid applying excessive downward pressure. Overloading the motor increases heat in the spindle, which can degrade the lubricants in the bearings and lead to the freewheeling issue.