My 76 corvette has a vibration in the rear at around 45 mph and it gets worse the faster you go. I had the tires all balanced and both the inner and outer wheel bearings have been replaced about 3000 miles ago. Would my old cracked worn out bushings in the suspension cause any of this. The only other thing I can think of is the smaller side axle shaft and the main driveline might be out of balance. Anyone else ever run into this problem with their C3.