Felt vibration at speeds >= 45 mph
 

I have a 1984 300D TurboDiesel with recently replaced engine mounts and engine shocks. At approximately 43-45 mph and greater I feel a vibration that creates a beat frequency (low pitch) with the engine. The service shop said that they balanced the tires. After driving about 500 miles, I sense the vibration is associated with tires/wheels, but I am not sure. I can shift to neutral at highway speeds (down hills and such) with ~800 rpm engine idle. The vibration remains distinct. The lead Mercedes technician does not suspect a drive shaft imbalance. How should I proceed to troubleshoot and remedy this problem with the least cost?
Thanks,
Michael Smith

I believe it is STILL a balance problem.

Does your shop have a dynamic balancer (i.e. the type that spins the wheel/tire?).

Balancing is the cheapest route here, and I would visit a dedicaed wheel/tire shop and have yours dynamically balanced.

Also, how worn are your tires? If you have an internal cord/tread separation problem, it will manifest itself as shimmy/vibration.

Are your tires stock size/height width. If not, you could be "out of spec"...meaning the tires are outside of the parameters that your suspension is designed for. This shows itself around that speed range as well.

Does it shimmy all the time at that speed range or just when cornering. If just when turning the wheel, then it may be worn control arm bushings.

Those are just some areas to look.