do you live on a hill? if so have some bricks ready to chock the wheels or alternativley put it in 1st gear or both. You need to check the linkage works by getting under the vehicle and have an assistant use the handbrake a number of times. If it appears to be working then it could be you have worn shoes in the drum. To remove there should be two threads on the face of the drum and a hole to back off the shoe adjuster so the drum can be removed. Pull it and rest it somewhere along the propshaft. Look at your shoes.