Hi Otahome,
I feel your pain. So you get vibration between 40-60 mph when cold. After a few miles it goes away.
This is what I have done:
- Replaced Gearbox Mounts
- Replace collapsed engine mounts
- Replaced Center Prop-shaft Support Bearing
- Prop-shaft couplings front and back
- Gearbox mount
- Front wheel bearings
- Front LCA's
- Rear front-sub-frame mounts - these are hydraulic and because of the power of the E55, these are common
- Rear Axle Housing to rear subframe, front mount changed
However, none of these helped the underlying problem, they made things better, but my vibration was still there, 45-65 then silky smooth.
After delving more I noticed that when I reversed the car up onto a set of car ramps (Car stone cold), and then drove it off, the vibration all went away completely. (I was checking and looking for more pointers under the car). However, the vibration came back the next day.
So this together with the help of a very helpful chap, DaveCr, from the UKMBOC (UK Mercedes Owners Club), we tracked it down to the shims that are fitted to the front differential mount (P/N A1403504941). They alter the angle the rear diff is connected to the prop-shaft. My one had a 3mm shim fitted from the factory.
So these shims are available from Mercedes in 1, 2, 3 and 4mm. I removed mine and started off with 2mm, drove it, it a little difference, but not to the point that I could accept. I then put in a 1mm, even better. But could do with more... so I removed it completely - no shim - perfect! The vibration is only noticeable if you listened for it. Last week I took it out for a quick blast and I could barely notice it!
Just as a experiment, I added a 4 mm shim, I tried it and the vibration was back big style! So I removed all the shims and now its the best it has even been.
Hope that helps.
Regards