Grinding the brake drum

Sooo, so now I can repair the scooter from the child. A lady had driven it over while parking. Now I noticed after a test drive that the rear brake does not reach correctly. The pads are changed, but makes no difference. When the full pass it simply continues and needs 50m at approx.30Kmh. I want to take the whole apart now and roughen the drum inside with 120er sandpaper, I did not do that for a very long time. is it still up?