Reference

Brake and Wheel Components

• Why is there discoloration on my brake bleeder valve?

  The fittings are covered with a special cadmium plating with a phosphate coating. The coating provides the best possible corrosion protection for use with magnesium brake castings in a wet environment. The white deposits are phosphate crystals that form from a phosphate sealing process which helps prevent corrosion when installed in magnesium alloy. The white deposits are not corrosion and will not harm the installation. If needed to reduce tightness during installation, the crystals can be softened using plain hot water and a tooth brush. Use the required thread sealants as specified by the appropriate aircraft service manuals.