A latch driving unit is assembled in an exterior knob assembly of a door lock. The latch driving unit includes a pin, a resilient member, a locking disk, a rotatable disk, a torsion spring, a cap and a strip. The strip removably extends through the cap, torsion spring, rotatable disk, locking disk, resilient member and the pin. If the strip is bent with an incorrect length, it can be removed from the latch driving unit and replaced with an intact strip. Thus, the exterior knob assembly is still useful after replacing the strip, and waste is avoided.