Instead of silicone, try the blue goo they sell at all auto parts, usually in a little tear pack at the counter. It is an alcohol-based mixture, similar to Permatex "gasket sealant". Most pads for newer cars come w/ a plastic pad on the back to prevent chatter, but I still smear the goo. I assume you lub'ed the caliper sliders. There is a special packet for that (silicone grease?), also usually at the counter. I haven't worked on 73+ A-body calipers, but re-installed the calipers on my 96 Voyager yesterday, which has rubber bellows to protect the slider bolts and grease.