my impact driver seems weak, it struggles on 3 inch deck screws that it used to zip right in.

Diagnosis

This loss of torque in the DCF887B is typically caused by one of three failure points: voltage sag from degraded battery cells, carbon buildup in the motor housing, or a failure in the internal hammer mechanism. When you notice a struggle with 3-inch deck screws—which require significant sustained torque—it usually means the tool is no longer achieving its peak RPM before the impact mechanism engages, or the impact mechanism itself is slipping. If the tool sounds "hollow" or the hammering sounds slower and less rhythmic than usual, you are likely dealing with a lubrication failure in the anvil or a worn-out brush set. Because the DCF887B is a brushed motor tool, the carbon brushes physically wear down over time, creating a gap between the brush and the commutator. This increases electrical resistance, which manifests as a noticeable drop in power under heavy loads, even if the tool seems to spin fine when there is no resistance.

How to Fix It

To restore the driving power of your DCF887B, follow these precise steps to isolate and resolve the power loss:

1. Battery Stress Test: Remove your current battery and swap in a high-output 20V MAX 5.0Ah or 6.0Ah battery that has been charged to 100%. Small 2.0Ah batteries often cannot provide the high current (amperage) required to drive 3-inch screws through pressure-treated lumber, leading to premature stalling.
2. Speed Selector Reset: Ensure the torque selector switch (located on the side of the tool) is clicked firmly into position 3 (High). If the switch is slightly out of alignment or stuck between positions, the tool may be defaulting to a lower power setting.
3. Collet Inspection: Open the 1/4" hex chuck and inspect the socket for debris. Insert a fresh, high-quality impact-rated bit. If the bit is worn or "rounded," the tool will slip internally, making the motor seem weak when the issue is actually a loss of friction at the bit interface.
4. Motor Vent Cleaning: Use a can of compressed air to blow out the motor vents at the rear and sides of the tool. Dust buildup inside the DCF887B housing traps heat, causing the motor to thermally throttle or lose efficiency during heavy-duty driving.

If That Didn't Work

• Replace the Carbon Brushes: If you have a multimeter, check for continuity. If the brushes are worn down to less than 1/4 inch, they will not make a strong enough connection to the commutator. You will need to open the casing, remove the old brushes, and install a new set of DeWalt-compatible carbon brushes to restore full electrical current to the motor.
• Lubricate the Hammer Mechanism: The internal striking plate can become gummed up with sawdust and old grease. Apply a small amount of high-grade lithium grease to the anvil area and run the tool in reverse and forward several times to redistribute the lubricant. This often restores the "snap" of the impact mechanism.
• Check for Internal Gear Wear: If you hear a grinding noise accompanying the lack of power, a planetary gear may have chipped. This requires a teardown of the gear housing. If the gears are stripped, the tool cannot convert motor RPM into torque, and the gear assembly must be replaced.
• Battery Terminal Cleaning: Use a cotton swab dipped in isopropyl alcohol to clean the copper contact rails inside the battery port and on the battery itself. Carbon buildup or oxidation on these rails creates resistance, preventing the tool from drawing the maximum wattage needed for long screws.

Heads Up

• Avoid "Over-Driving": Do not force the tool to drive a screw if it begins to stall; this generates extreme heat in the brushed motor and can burn out the windings permanently.
• Battery Rotation: To prevent "voltage sag" in your fleet, avoid using the same battery for every heavy project. Rotate between 3-4 batteries to ensure no single pack is chronically over-discharged.
• Bit Quality: Always use "Impact Rated" bits. Standard bits can flex under the torque of the DCF887B, which absorbs the energy and makes the tool feel weaker than it actually is.
• Storage: Store your tool in a dry environment. Moisture can lead to corrosion on the commutator, which causes "arcing" and permanent power loss.