make sure you slacken the hand brake cable off first then remove them from the calipers.fit the new pads and only screw the pistons back until the caliper can be slid back on with about 1mm gap make sure if the pads have a lug on them that it lines up with the gap on the piston face, then with your hand pump the hand brake lever on the caliper until it make a good firm contact with the pad, refit the hand brake cables and pump the foot pedal to also make sure the piston is locking the rear discs up and is free when you take your foot off. you will need about 6 to 7 clicks on the hand brake for it to work correctly. but if your not sure get a garage to do this job.
Richie
December 2007