first timer here. i've got this problem with my mini. the steering wheel shakes when it hits 50 mph. it's not the balancing, so don't even try. the mechanics are stumped, and the closest dealership is about 5 hrs away. if you've got any ideas, let me know.

 

A shake in the steering is usually either an out of balance wheel (which you say you've had checked) or alignment. If it's not either of those, it could be a bad tire. After that, I guess the next place to look would be in the suspension?

 

Does it go away if you go fast enough? Have you tried swapping the wheels front to back ti see if it changes? That would eliminate tires and wheels.

If it's not the tires/wheels it's going to be one of these:

Strut tower mounts/bushings
Struts
Tie rods
Control arm bushings
Ball joint?

If your car has a few miles on it my money is on strut tower mounts. Find a mechanic that is familiar with older BMWs, they are used to this problem.

 

if youve got warranty, i'd say let them sort it out. you should be able to get a loaner car from the dealer...