Wet & dry[edit]A wet clutch is immersed in a cooling lubricating fluid that also keeps surfaces clean and provides smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch discs can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged. The Hele-Shaw clutch was a wet clutch that relied entirely on viscous effects, rather than on friction.[1]
A dry clutch, as the name implies, is not bathed in liquid and should be, literally, dry.