OK, my bad, I may have had a brain fart here (it's been a long day). Anyway, I most likely got confused with the rear brakes, and looking at the parts lists I'm sure thats the case as they don't even sell a shim kit for the front brakes on the 850, only the rear. The shims are seperate, thin pieces of metal that slip between the caliper and the pad backing. They do sell a hardware kit for the fronts that includes new springs, which is the piece that you mention which attaches to the back of the pad and locates and centers the pad on the piston. So take back what I said about the shims on the front. I did the fronts on my 850 over a year and a half ago, so I can't rightly remember exactly how things looked in there.

However, you could still try using some of the high temp silicone grease they sell as brake anti-squeal compound. Most good parts stores carry this, just coat the back face of the pads (the metal backing) with this stuff. I have also noticed, from reading this forum for awhile now, that the 850 seems to be very finicky when it comes to brake pad compound and squeal. Some people say they run the stock pads and are fine, others say they squeal. Some people recommend EBC, Hawk, or other high performance pad types, others the cermanic pads, everyone seems to have different experiences. When I got my car the fronts did squeal a little, but my bigger problem was the amount of dust being generated by the factory pads. I was cleaning my wheels every few days or they were black. Fortunately, the pads were worn so I replaced them not to long after buying the car. I went with Axxis pads (Axxis is the Aussie division of PBR/metal master, got them off ebay) on the stock rotors and have been very satisfied. Braking performance is at least as good if not better as with the stock pads, dust generation has been dramatically cut, and no squeal.