I have a 67 Mustang convertible that I've owned since 1976. Over the past several years I've had the front end rebuilt including new Borgeson power steering system installed and new shocks. Also, about ten years ago I had the drive shaft balanced. I have had a vibration in the car at around 42 mph that goes away as you increase speed. I just replace all four tires and obviously had them balanced. Now the vibration is gone at 42, but starts at 70 and goes away after 72, the perfect cruising speed. I'm going back to the Discount Tire to have them rebalance and rotate the tires. Anyone have ideas on what else I should look for. Seems like the vibration is more in the steering wheel than the seat if that helps. Could this be a U-joint issue, or bad steel styled wheel (not original)? Or drive shaft? ANy comments would be appreciated.