If I don't drive my 84 500SEL for say a week, I notice a drive line vibration for about the first 5 miles at about 45 to 60 mph. After that, it is smooth. I tried putting the trans in neutral at about 60 mph and let the engine come back to idel and the problem was still there. If I drive the car every day, it has no vibrations. Anyone run across anything like this? Flex disk, center bearing and carrier were replaced about 5 years ago (maybe 25000 miles).

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84 500 SEL (307,xxx miles)