can i rinse the head of my m12 ratchet under water to clean out grease and metal chips? it's packed full.

Diagnosis

The Milwaukee M12 FUEL 3/8" Ratchet (2557-20) is designed with an open-architecture head to allow for heat dissipation and rapid movement, but it is not an IP-rated waterproof tool. The head assembly consists of a planetary gear set and a drive anvil that are lubricated with a high-viscosity synthetic grease. There are no hermetic seals between the gear housing and the internal motor housing. If you rinse the head under a faucet or pressure washer, water will migrate via capillary action past the drive anvil seals and directly into the motor windings and the trigger switch assembly. Because the tool uses a brushless motor, water ingress can cause immediate short-circuiting of the electronic control module. Furthermore, water will emulsify the internal gear grease, breaking down its lubricating properties and leading to rapid metal-on-metal wear of the planetary gears, which will eventually result in the tool "slipping" under load or seizing entirely.

How to Fix It

To safely remove metal chips and excess grease without destroying the electronics, follow this dry-cleaning protocol:

1. Remove the M12 battery pack immediately to eliminate any electrical current from the circuit board.
2. Invert the tool so the anvil (the square drive) is facing downward. This ensures that gravity pulls debris away from the motor housing.
3. Use a stiff-bristled nylon parts brush or a brass wire brush to scrub the exterior of the head, focusing on the gaps where metal shavings have packed into the housing.
4. Use a can of compressed air or a shop compressor set to no more than 30 PSI. Direct the air blast from the anvil end, blowing "outward" through the gear housing. Do not blow air directly into the trigger switch gaps.
5. For heavy grease buildup, dampen a lint-free microfiber cloth with a small amount of isopropyl alcohol (90% or higher). Wipe the exterior of the head. The alcohol will break down the grease and evaporate quickly without leaving conductive residue.
6. Once the debris is cleared, use a vacuum with a narrow crevice tool to suck out any remaining particles from the head area.

If That Didn't Work

• If the debris is packed too tightly for compressed air, use a dental pick or a thin needle to manually pry out the metal chunks from the perimeter of the anvil. Work slowly to avoid scratching the hardened steel of the drive square.
• If the tool is already contaminated with oil or heavy chemicals, use a dedicated electrical contact cleaner spray. Spray it sparingly on the exterior of the head; these solvents are designed to displace moisture and evaporate without leaving a film that attracts more dust.
• If you suspect water has already entered the tool, do not attempt to power it on. Remove the battery and place the tool in a drying cabinet or in front of a dehumidifier for 48 hours. Attempting to run a wet motor can cause an arc-flash that permanently fries the PCB.
• If the tool feels "gritty" during operation after cleaning, the internal grease may be contaminated. In this case, the tool must be disassembled to clean the planetary gears and repacked with a high-pressure lithium-based grease.

Heads Up

• Never use a pressure washer or a garden hose on any M12 FUEL power tool; the pressure forces contaminants deep into the motor windings where they cannot be removed.
• Avoid using WD-40 as a cleaner on the head; while it removes grease, it can degrade certain plastic components and attract more metallic dust, creating an abrasive paste.
• Check the anvil for rounding or cracks every time you perform a deep clean; metal chips often indicate that a socket is wearing down or the anvil is taking too much lateral stress.
• Keep the tool in a dedicated case when not in use to prevent metal shavings from the shop floor from migrating into the head assembly.