Teardown: Water-Damaged Makita Cordless Screwdriver

Complete teardown, solvent flush, and planetary gear rebuild after a 5-minute deep water submersion.

The Emergency

Storing the cordless screwdriver near the laundry resulted in a severe liquid intrusion event, with the tool spending several minutes submerged in detergent water. Upon discovery, I immediately disassembled the screwdriver, wiped down the standing water, and sealed the internal components in a bag with silica gel packets to draw out ambient moisture while formulating a recovery plan.

Analysis

The water ingress was extensive. A diagnostic teardown revealed water pooling across the PCB and battery housing, with the primary DC motor suffering the most severe flooding.

The Motor Cleanup

To displace the moisture inside the motor and surrounding components, I applied a generous coating of WD-40. To mechanically extract the internal liquids, I fastened an external drill to the flooded motor’s shaft and operated it at high speeds, utilizing centrifugal force to physically drive the water out. The motor was subsequently flushed with 99.9% Isopropyl Alcohol (IPA) and spun again.

Cleaning The Rest

The remaining components were also treated with WD-40 and IPA to strip away oily residues and lingering mineral deposits from the detergent, resulting in a completely dry, clean surface.

Mechanical Re-Lubrication

While the WD-40 successfully mitigated the water damage, its solvent properties completely dissolved the factory grease within the planetary gear assembly. To resolve this, all gears were meticulously cleaned and re-lubricated using a plastic-safe lithium grease before reassembling the main motor housing.

The Final Rebuild

To prevent torque shear during final assembly, I carefully applied cyanoacrylate to the plastic motor mounting plate. This acted as a liquid thread-locker, ensuring the screws bit firmly into their original threads without stripping the housing. The tool is now fully operational with zero alignment play.