A reciprocating pump and transmission assembly having a one-way clutch is disclosed. The transmission includes an input shaft with an eccentric element, a drive link rotatably connected at one end to the eccentric element and at the other to a driven arm. The driven arm is connected to a driven shaft via a one-way clutch. The oscillating motion of the eccentric drives the drive link and driven arm and the one-way clutch translates that motion into incremental motion of the driven shaft. By changing the stroke length of the drive link various gear ratios between the drive shaft and driven shaft are achieved. The driven shaft then uses a mechanism such as a Scotch Yoke to create reciprocating motion to drive one or more pumping elements.