Guess what, I have a 84 500SEL, 91 300D, and a friend has an 87 420SEL and another friend has an 88(?) 300E, and all have the exact same problem. Same speed, only when accelerating, and 1st or 2nd gear. I have learned to accept it as normal. If someone comes up with a fix, I would love to hear about it. By the way, my 84 500SEL has all new engine, trans, differential mounts, new flex disk and new center support mount and bearing, and rebuilt driveshaft.

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84 500 SEL (307,xxx miles)