Note the glaze, scoring, and light grooves on this rear brake drum. After dust cleanup, measure the diameter of the drum at several places. Compare these measurements to the maximum allowable size. If the drum can be resurfaced within factory diameter limits, do so. Operating a drum beyond the maximum recommended diameter can cause poor braking and lead to drum failure. Check for hard spots, warp, and deep scoring grooves. A brake shop or automotive machine shop can resurface drums.