The bushing in the distributor that supports the shaft wears out and that begins to happen. If you can buy the bushings, used to be able to order from Napa And GM but I believe GM no longer sells them. anyway if you can buy them buy two and press both of them in and you will never have the problem again. They used to cost about a buck and a half. They are very easy to push in and even if the shaft has some wear the second bushing will solve the problem.
