Hi thunder. Welcome to the forum. The holes in the rotors have no affect on how they're machined. They don't improve stopping directly either. There is less surface contact area, but the difference is negligible. What they do is improve cooling which reduces gasing of the friction linings which reduces one type of brake fade. Mountain driving is where you'll really notice the difference.
As for the shimmy, when does it occur? All the time or just when braking? Does it shake the steering wheel or do you just feel it in the seat? It is real common for new rotors to warp and once they're machined, they generally don't warp again. This is especially true of Chinese rotors. There's nothing wrong with them except cast iron parts made here are "aged" for 90 days before the final machining. Chinese rotors are cast, packaged, and shipped. The aging takes place on your car.
If the shimmy occurs all the time, have the steering and suspension components inspected by an alignment specialist. GM vehicles eat ball joints faster than most other brands. Also look for a broken belt in a tire. You will feel that at all speeds. Often you will see the steering wheel oscillate back and forth as you drive through a parking lot. Warped rotors can do the same thing if the calipers aren't sliding freely on their mounts, but usually you'll only feel that when braking.
Monday, July 26th, 2010 AT 5:25 PM