This was a common problem with the E36.

Sometimes, when braking, the wheel would shimmy, and it was very annoying. A lot of people complained about this.

Opinions differed as to the cause. Some claimed it was "warped" brake rotors and others went further to say they were warped by not torquing the lug bolts evenly or by using an air impact wrench instead of a torque wrench.

The problem would come and go, however, which is weird, as if it was a warped rotor, you'd think it would do it all the time.

Some folks pointed out that when braking very hard and then holding the brakes on, some types of pads would leave an "imprint" on the rotor surface. Their theory was that this imprint caused the rotor to "catch" slightly on subsequent braking, which would cause a shimmy since the rotors were no longer in sync, and each caliper would "grab" at a different part of the revolution.

Their solution was to run the car up to speed on an empty stretch of road, apply the brakes firmly to "burn off" this pad imprint, and then release the brakes so a new imprint didn't form. Oddly enough, this seemed to work on one of my cars that had this problem.

Changing pad types (and putting on new rotors) seemed to fix the problem permanently.

Check your wheel balance, too, as well as tire age. Like I said, those old Michelin's were about as hard as the wheels on Fred Flintstone's car.

Good Luck!

P.S. - bottom line, is, though, it is hard to get back that "new car feel" on a car that is 10 years old and has 150,000 miles. Drive the wheels off it and use it up. Move on to the next car.