a slip clutch acts between a shaft and a housing . the slip clutch includes an oil reservoir within the housing and one or more slipping surfaces disposed in the oil reservoir that are keyed to the shaft and possibly alternately to the housing . the slipping surfaces may include stacked plates or washers . each of the washers includes an oil groove or other structure on one surface thereof that maintains a consistent film of oil on the washer surfaces . the stacked washers slip relative to one another such that the shaft rotates relative to the housing upon an application of torque that exceeds a predetermined torque .