1991 500SL vibration at speed
 

My 91 500SL has a vibration between 58 and 65 MPH the wheels and tires ars balanced perfect and I suspect possible driveshaft vibration. The rear halfshafts feel good and the boots are perfect. Could the driveshaft rubber couplers be the colpret even though the appear to be in good shape. Any suggestions on a fix ??????

I have the same scenario on my 1995 SL500. Same speed too. New tires, balanced, new wheel bearings, brand new drive shaft, new brakes and rotors, new front struts and new motor/transmission mounts. Still have the issue. I find that the vibration is there when the tires are cold. Tires are Michelin Pilots. Once the tires heat up the vibration goes away. I live in Florida so the tires heat up pretty quick. It's definetly annoying but unless I'm missing something and I might be, we'll have to live with it.

My 1991 300SL had the vibration issue also. It was very pronounced just before each up shift and then at higher speed cruising. I first rotated the tires, as it seemed to be better after the car was driven a bit. But that didn't help. Next I replaced the flex couplings, as they showed signs of cracking, but that didn't help. It turned out to be the drive shaft hanger bearing. It's not easy to see, as on the 300SL, it was necessary to drop the exhaust pipes out of the way for access. But it cured the problem.