Vibration at particular speeds has to be something rotating.

Bent wheels, out of round or misshapen tires, bad wheel bearings, bad driveshaft, bad rear half-shafts, etc.

On the front of the car, anything loose will do the same thing -- bad ball joints, bad tie rod ends, bad idler arm (if it's tight, it's OK), loose steering box, bad control arm bushings, bad track rod bushings.

Vibrations at specific speeds usually end up being tires or wheels -- at whatever speed the vibrations turns up the wheel movement and the natrual vibration harmonic of the suspension match, so it shows up at higher energy than the shocks can dampen. At other speeds, it won't reinforce the same way so it is much less.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!