A windshield wiper drive mechanism includes a crank driven by a motor shaft and having, towards the end of the crank remote from the motor shaft, a crank pin carrying an eccentric crank head piece on which a crosshead is pivoted. The head piece carries a latch which includes a latch finger movable under the action of a resilient member and arranged to leave the crank head piece free to move with respect to the crank when the latter is rotating in a first direction, but to prevent such relative rotation when the crank is rotating in the opposite direction. The latch finger includes a radial latch arm extending outwardly, while the crosshead has a recess for receiving the latch arm. The crank head piece has an opening for receiving the free end of the latch finger. The latch arm is so positioned, and is of such thickness, that, when the latch finger is engaged in the opening in the crank, the latch arm lies between the face to face surfaces of the crosshead and of the crank. The crank head piece is placed so as to face towards the crank.