My '89 Brougham has a vibration that begins at 50 mph and gets worse as I go faster. By 70, it is really bad. It initially felt like bad universal joints, so I replaced them. I also cleaned all the dirt and grease off of the drive shaft. The same vibration was still there. I had the tires rotated and re-balanced. I replaced all four shock absorbers (which it needed anyway). None of this helped. Today, I replaced the rear transmission mount and that eliminated some, but not all, of the vibration. I had the car on a lift and I let it idle in drive and watched the drive shaft. The front end of the shaft seemed to be moving up and down as it turned. Both the balance weights are still there. Could the yoke be bent or worn? Is there a bushing in the tail end of the transmission that could wear out? If there is, can it be removed & replaced without dismantling the entire tranny? There is no separate tail cone on that model transmission. Today is Saturday and we are taking the car on a long trip on Wednesday, so I need to get this sorted out. Any advice would be greatly appreciated.