dewalt drill won't change from forward to reverse, the selector switch feels stuck or just spins.

Diagnosis

The failure of the forward/reverse selector switch on the DeWalt DCD800B usually stems from one of two distinct issues: external contamination or internal mechanical shear. In high-dust environments—such as drywall installation or masonry drilling—fine particulate matter migrates through the housing gaps and settles into the sliding track of the selector. This creates a physical blockage that prevents the switch from locking into the forward or reverse detents, making the switch feel "gritty" or stuck in a neutral center position. If the switch spins freely without any resistance or fails to engage the motor, the root cause is likely a sheared plastic tab or a dislodged spring within the selector assembly. The DCD800B uses a sliding mechanism that must physically move a lever to reverse the polarity of the brushless motor controller. When this internal linkage snaps or slips out of its groove, the external slider moves independently of the internal switch, resulting in a tool that stays in one direction regardless of the switch position. You can confirm this by observing if the slider "clicks" into place; if there is no tactile snap, the internal detent spring is likely broken.

How to Fix It

Follow these steps to clear debris and reset the mechanism. If the switch is physically broken, you will need to replace the selector assembly.

1. Power Down: Remove the 20V Max battery pack immediately to prevent accidental trigger pulls during the cleaning process.
2. External Debris Purge: Use a can of high-pressure compressed air or an air compressor with a nozzle. Direct the air stream specifically into the gaps around the base of the selector switch while rapidly sliding the switch back and forth. This breaks up compacted dust and pushes it out of the housing.
3. Solvent Flush: If the switch is sticky due to oils or adhesives, apply a small amount of electronic-grade contact cleaner (such as QD Electronic Cleaner) around the switch. Avoid using WD-40, as it attracts more dust over time. Work the switch back and forth for 60 seconds to allow the solvent to penetrate the internal slider.
4. Mechanical Reset: With the battery still removed, apply firm (but not excessive) pressure to the switch, pushing it fully to the left, then fully to the right. If you feel a "pop," the slider may have simply jumped its track and has now reseated.
5. Testing: Reinsert the battery. Test the trigger in both directions. If the drill only runs in one direction despite the switch being moved, the internal linkage is sheared and requires a part replacement.

If That Didn't Work

If the cleaning process fails to restore functionality, try these advanced recovery methods:

• Full Housing Disassembly: Remove the T10 Torx screws securing the outer casing of the DCD800B. Carefully split the clamshell to access the internal chassis. Inspect the selector slider for a broken plastic finger. If the finger is snapped, the entire selector assembly must be replaced.
• Spring Tension Check: Locate the small tension spring that holds the selector in the detent position. If the spring has popped out of its seat, use a pair of needle-nose pliers to carefully reposition it into the guide slot.
• Contact Cleaning: Use a fine-grit sanding stick or a cotton swab with isopropyl alcohol to clean the electrical contacts that the selector switch interacts with. Carbon buildup on these contacts can either block the signal or cause the tool to behave erratically.
• Replacement Part Installation: If the plastic internal components are cracked, order a replacement Forward/Reverse Switch assembly specific to the DCD800 series. Ensure the new switch is seated perfectly flush against the motor housing before closing the case to avoid binding.

Heads Up

• Avoid Lubricants: Never apply heavy grease or oil to the selector switch. This creates a "sludge" when mixed with job-site dust, which will permanently seize the mechanism.
• Impact Warning: Avoid resting the drill on its side on hard concrete surfaces; a side-impact can bend the selector slider, making it permanently stick in the neutral position.
• Trigger Safety: Always ensure the selector is fully engaged in either Forward or Reverse before pulling the trigger. Operating the tool in a "halfway" neutral position can cause electrical arcing within the brushless controller.
• Dust Management: Periodically blow out the tool housing with compressed air every 20-30 hours of heavy use to prevent particulate buildup in the switch and trigger assemblies.