I had the minivan in for a muffler yesterday and asked the mechanic to switch the tires front to back. So, with the "new" used tire on the right front and known good tire from the left rear to the left front,eliminated the "shake" !! I had two bad front tires. Who wuddha thunk that? It was the cheapest alternative to check the tires first. Thanks to all!! P.S. I let the shop do my exhaust work because they're better equipped. A muffler,an exhaust splice about 6'' long, rotation of the two tires and labor was $60. here in rural Minnesota, and no headache for me!