chock your front wheels, jack rear of car up on to axle stands, remove brake calipar, taking care not to put any strain on flexi hose, remove small holding grub screw, and tap old disk off, clean area, and fitting is in reverse order, you will need to turn the piston back to allow new pads to fit. and make sure you replace both rear disks & pads.
hope it helps, September 2010
