find an empty parking lot and idle around with the brake applied. do it in reverse as well. you might find that by working through the outer layer on the pads, you'll get into some material that will bite. you have to heat, cool and bed service brakes when you change them. (with good pads, anyways) maybe your parking brake pad needs the same thing. alternatively (and harder) is remove the drum, and sand the face of the two pads to get rid of the smooth, shiny assembly line finish? i can lock-up my wheels on all of my rides, and do wicked brodies (if i wanna) with the parking brake. if you can't you haven't got the mating surfaces ready for each-other. last thing, take the parking pads out, and lay them inside the drum. do they make full contact across their entire wear surfaces? if not you have the wrong pads for the drums.