post up a pic, "centre pull brake" covers a lot of brakes, is it a u brake?, if so, as kevs says if you got em set up right then you should be able to stop the bike and you with one finger , two finger grip will lock the wheel solid , i run superstar u brake with cheap jagwire blocks , blocks are from car spares shop look like old oddy blocks with fin on one side , no squeeeeeeeeeek and bite real well on the rim ,u brakes should work well even on a dirty rim because of the power they generate.