Hmm...are you taking your car to Midas? just kiddin'

Vibration in the steering wheel when braking is due to a few things
1. either excessive runout in the rotor(s) (most often noticed with a occillating steering wheel)
2. either excessive parallelism in the rotor(s) (most often noticed with a pulsating pedal)
3. bad wheel bearings

A ball joint could possibly cause a vibration, however it depends on how bad it is and most often a bad ball joint on the 240 will click when going over bumps at low speeds, not vibrate the steering wheel, at least not on a 240.

TIP: whenever replacing pads ALWAYS!!! either replace rotors or machine rotors to true. A new rotor DOES NOT need to be machined, regardless of what shop tells you so, they are already done the best they can be at the factory and the finish on them is the best they can be.

I would have your wheel bearings checked or do them yourself, a shop manual has an easy procedure for this.

REAR BRAKES HAVE NOTHING TO DO WITH VIBRATION WHEN BRAKING!!! they only do about 20-30% of the braking and regardless, ask yourself how would the rear brakes affect your steering wheel???? eh?

Good luck!

Chuck
(Now ASE certified in Brakes and Electrical! YAY)

--
'88 244 174K, '87 BMW 325e 180K (used to feed a '84 245, '84 244, '85 744)