Q: I am changing the rear break pads. when winding back the piston does the handbrake need to be on or off?

When turning in the rear calipers you should use the caliper tool to turn and push back the piston in the caliper. You should have the parking brake cable released at all times when turning back the pistons. Once the new pads are installed and caliper is installed then pump the brakes using only short strokes. Do not push the pedal all the way down or master cylinder may be damaged. Pump up brakes and when pedal gets hard then hold brake down and then pull up in the parking brake a few times to make sure it works.

The parking brake lever inside the vehicle should be released. Compressing the piston with the parking brake engaged can result in a parking brake that is out of adjustment, if it will compress at all. More than likely, you will not be able to remove the caliper with the parking brake engaged anyway. If you feel you could use a hand in changing out your rear brakes, contact a certified mechanic, like the ones available at YourMechanic.com.