how do i replace rear brake pad's for renault scenic 2005 model ?

Undo the caliper from its holding bracket (2 bolts) and lift the caliper away. Remove the old pads - they may be tight - and clean everything up. To replace the new pads, the caliper piston has to be turned clockwise as it is pushed in, and there is a special rewind tool for this. Laser tools do one. You could get by without this tool but you can risk damage to the caliper so I recommend that you use it.

John
April 2009