Abstract: In a windshield wiper drive system of the type having a reciprocating drive link and a reversible electric motor, a variable throw crank arm assembly between the drive link and the motor drive shaft including a first arm rigidly attached to the drive shaft, a second arm pivotally attached to the first arm and to an end of the drive link, a guide follower on the second arm, and a guide channel on the motor housing receiving the guide follower. The guide channel has a circular portion centered on the drive shaft axis and a noncircular escape portion radially outboard of the circular portion and merging therewith at a junction. When the drive shaft rotates continuously in one direction, the guide follower traverses the circular portion and holds the second arm in a short-throw folded position relative to the first arm.