have a power steering pump whining badly on my 01 dakota 4.7 4x4. went to advance auto parts and they show 2 different types of power steering pumps for the 01 dakota's. one is an 18mm pulley type and the other is a 17mm pulley type. does anyone know how to tell which one fits which truck without taking off the pump and taking it in to the auto parts store? this is a special order item. i measured as best i could the shaft with a pair of calipers and i think it is 17mm, but i am not sure!!!

thanx in advance for your help!!