A box of misc. hardware that I bought from a gone out of business bike shop had some "T" shaped brackets that are made to keep the rack from sliding down the seat stays. They are about 1" wide at the top, and 2" long. The top holes line up with the Pletscher rack, and the brake bolt goes in one of the bottom holes. With the bracket, you don't have to overtighten the clamp bolts, just enough to not wobble side-to-side.