Many times the shaft shears off at the very bottom tip area. The camshaft still turns the rest of the shaft, including the top half which turns the distributor. I have seen it happen several times on 318s, curiously the ones I have seen have all been early 80s units. I have found that a large piece of debris gets into the pump and locks it up. The shaft then shears. So, even if that is the problem: sheared oil pump drive shaft, the oil pump & pickup will need to be replaced. If the debris somehow dislodged after the shaft sheared, you could get lucky, but I would expect the oil flow to pull it back in. Jeff Ruffing 65 Imperial Crown covert ASE Master Technician 8+ year Chrysler Master Technician