on most brake systems, the caliper or the disc must float, to allow play when no pressure is applied, and promote even brake pad wear
i'm not exactly familiar with the R brake system, but most use a sliding caliper/solid disc system
you'll need to pull that caliper to clean & lube the slide pins/rubber boots, or replace them if needed
just for reference, the stock 88-02 blaster uses a solid brake caliper and a floating disc, they can sometimes need the disc removed and splines cleaned/lubed for proper operation, among the other constant attention needed for them to work