A vibration felt through the center floor of the vehicle can be caused by cracked and/or shredded driveshaft flex discs, resulting in excessive driveshaft movement. If not repaired, damage to the driveshaft center support bearing, transmission, or differential can occur.Google+
Car Problem Reports
Mercedes-Benz CL500 Cracked Driveshaft Flex Discs May Cause Driveshaft Movement/Vibration
Mercedes-Benz CL500 Problem
Average Mileage: 120,452 mi (48,250 mi - 225,558 mi)
Visitor, 2001 Mercedes-Benz CL500, 151,000 mi
it vibrates at a speed 40 to 80 how much to replace
Visitor, 2004 Mercedes-Benz CL500, 48,250 mi
Just had an inspection that indicated a crack in the rear flex disk. Haven't had it fixed yet.
Vibrates Gear shift. It sounds like a light thump or low vibration that I only hear at low speeds, below 40 mph. It appears to be coming from rear suspension...