![Surprised :o](./images/smilies/icon_e_surprised.gif)
First, both the pads and the rotors were barely worn at all, as in I'll bet they didn't have more than 5,000 miles on them (I've barely driven the car since I bought it). I thought I had just wasted the cost of new pads & rotors because it must have been something else causing the shimmy. But, the shimmy is gone after replacing them. So, why would a nearly new set of pads/rotors behave like that? Well, I noticed that in between the rotor faces, in the channels, there was a tremendous amount of rust.
When I was using an impact screwdriver to loosen the rotor set screws, there must have been 200 or more huge flakes of rust come out of these channels on each rotor. I've seen rust on brake rotors before - the faces and top hat portions. But, I've never seen that kind of corrosion on the insides of a brake rotor. It was amazing and obviously the reason for the shimmy when the brakes were applied.
The second thing was on the inside of the caliper on the driver's side, the slot for the inside brake pad was too narrow. My son and I were doing the project, and I had him try to insert the new pad as I figured it must be something I was doing wrong (although not much to sliding in a new brake pad on a Porsche caliper). I tried all 4 of the new brake pads and they all were just a little too long. Then, I looked at the old brake pad that came out of that slot and noticed hammer marks all along the top edge of the brake pad backing. So, the last person who changed that brake pad apparently pounded the crap out of it to get it to go into the caliper. Rather than following suit, I grinded off a little of the pad backing plate on both ends on my bench grinder. Worked fine. I looked to see if there was any corrosion or dirt in there that was making the slot smaller, but I guess it is just that slot on that caliper is a couple of millimeters narrower than it is supposed to be.
I swear, in every job, there is one PITA surprise lurking: frozen bolt, stubborn electrical connector, whatever. But, it almost never fails that something makes an easy job tougher. At least in this case, there was an easy fix once the problem was identified.