my dewalt dcf887b impact driver sometimes makes a loud grinding noise and then just stops driving screws, battery is charged.

Diagnosis

This specific failure in the DeWalt DCF887B is typically caused by a catastrophic failure of the hammer and anvil assembly within the impact mechanism. In a brushless impact driver, the motor spins a set of internal weights (the hammer) that strike an anvil to create rotational torque. When you hear a loud grinding noise followed by a complete loss of driving power, it indicates that the hardened steel teeth or the spring-loaded retaining mechanism has sheared or stripped. This means the motor is still spinning the internal shaft, but the energy is not being transferred to the chuck; instead, the components are slipping and grinding against one another. You can confirm this by pulling the trigger while the tool is unloaded. If the motor whines or spins with a high-pitched sound but the 1/4" hex collet does not rotate, the mechanical link between the motor and the anvil is broken. If the tool intermittently works but "slips" under load, the hammer springs have likely lost tension or the anvil has developed a flat spot, preventing the impact cycle from completing. This is often exacerbated by using the tool for heavy-duty demolition or oversized fasteners that exceed the tool's rated torque capacity.

How to Fix It

Because the hammer and anvil are precision-machined components, they cannot be "repaired" with lubricants or adhesives; the entire gear and hammer assembly must be replaced. Follow these steps to replace the impact cartridge:

1. Remove the 20V battery and any bits from the chuck to ensure safety.
2. Carefully peel back the front rubber dust boot. Use a small flat-head screwdriver to gently pry the rubber away from the housing.
3. Locate the heavy-duty retaining ring (C-clip) situated behind the boot. Use a pair of snap-ring pliers to expand the ring and slide it off the shaft.
4. Unscrew the front nose collar. This may require a punch and hammer if the collar has become seized due to metal shavings from the grinding failure.
5. Slide the front chuck assembly forward and out of the housing.
6. Remove the four T10 Torx screws securing the motor housing to the outer shell. Split the casing carefully to avoid snapping the plastic alignment pins.
7. Extract the damaged hammer/anvil assembly. Note the orientation of the thrust washers and shims; these must be placed in the exact same order during reassembly to prevent the tool from overheating.
8. Insert the new impact mechanism assembly (compatible with the DCF887 series). Ensure the drive gear meshes perfectly with the brushless motor's pinion.
9. Reassemble the housing, tighten the T10 screws in a cross-pattern to ensure even pressure, and reinstall the nose collar and retaining ring.

If That Didn't Work

• Check the Brushless Controller (PCB). If the hammer assembly is new but the tool still stops under load, the MOSFETs on the control board may be overheating or failing. Look for scorched capacitors or a "burnt electronics" smell coming from the rear vents. If the PCB is fried, the tool will cut power as a safety measure to prevent the motor from burning out.
• Inspect the Motor Pinion Gear. If the grinding noise was extreme, the small gear on the end of the brushless motor may have stripped its teeth. If the pinion is worn, replacing the hammer assembly won't help because the motor cannot drive the new gears. You will need to replace the entire motor unit.
• Test with a high-discharge battery. A failing battery cell can cause a voltage drop that triggers the tool's internal protection circuit, making it seem like a mechanical failure. Try a fresh 5.0Ah or higher battery to rule out electrical sag.
• Verify the Collet Spring. If the tool spins but the bit falls out, the internal spring-loaded detent ball in the 1/4" chuck has failed. This is a separate issue from the hammer assembly but often happens simultaneously during a high-torque failure.

Heads Up

• Avoid using the DCF887B for "impact wrenching" tasks like removing rusted lug nuts; this tool is designed for driving screws and bolts, and excessive lateral force can warp the anvil.
• Periodically blow out the motor vents with compressed air. Metal shavings from a failing hammer assembly can migrate into the brushless motor, causing permanent magnetic damage.
• Never use penetrating oils or WD-40 inside the impact mechanism. These lubricants attract metal dust and grit, which act as an abrasive and accelerate the wear of the hammer teeth.
• When using the 3-speed selector, avoid staying in the highest torque setting for long periods of continuous driving, as this increases the heat load on the hammer springs.