TractorCo.com Overrunning Clutch

An overrunning PTO clutch is a device that allows a tractor's power take-off (PTO) shaft to be driven in one direction, but to spin freely (freewheel) in the other direction. The ratchet mechanism in an overrunning clutch is similar to the freewheel hub on a bicycle. The freewheel action of the overrunning clutch prevents equipment from "driving" the tractor through its PTO shaft. A typical example is a rotary mower (sometimes called a "bush hog") that is being operated behind a tractor with a transmission PTO. When the operator pushes the clutch to slow the tractor, the inertia of the spinning mower blades puts a force onto the PTO shaft. This force drives the tractor forward, potentially causing an unsafe situation.