HELP!! I have a shimmy over about 58MPH - can't feel it in the steering wheel or the transmission, and have noticed it for about a year now. It shimmys for a second, then stops, repeating about every 3 - 4 seconds. Since it started, I have changed the transmission (C4 to T5), shortened and balanced the driveline including new u-joints, new tires (balanced), new tie rod ends and front end alignment - and the shimmy is still there! It almost has to be something in the rear end, since all the changes up front didn't help. Any ideas?