shimmy

[waywin]

1997 E420 with 98,000 plus miles. Through 3 sets of tires, all different manufacturers, wheel alignments, 4-wheel, and more tire rotations and balances than I can count, this car still has a shimmy that frequently, but not always, occurs in the 50-60 MPH range. It is not violent but it is definitely there. It even can be felt at times when braking. The most disconcerting thing about it is the fact that it does not happen all of the time. I have discussed this with my dealer and 3 tire stores. I have had the original Michelins,and replacement Pirellis, Continentals and Bridgestones on the car and they all do it. The wheels are not damaged and neither is the suspension. It has never been in an accident. I love this car but this shimmy drives me crazy. The brake pads and rotors have always been replaced in sets. I cannot think of anything else that I can do or have done. Does anyone know of a similar problem? Is there something I've missed? My dealer alluded to having heard of this problem before but could offer no solutions other than computer balancing, which did not work.