Originally Posted by
seeker333
If Shimano hubs are immersed or take a direct hit from a hose on the drive side, then water is likely to get into the bearings. The grease will emulsify from the mixing action of the rotating ball bearings. Water in the bearing cavity can't escape quickly and the balls, cup and cone begin to corrode. After a short time they'll become noticeably rough, and most owners will start looking for a new hub at this point, since it's practically impossible to replace the pressed-in steel cup.
Their lack of immunity also applies to the solvents used to clean cassettes and chains that can seep their way through the freehub cavity into the bearings. A spray from the hose only helps the solvent on its journey. In my opinion and experience.