How do you retract brake cylinders on the rear of ed falcon?

1. Why can't I push the caliper piston back?
2. What tool can be used to retract the pistons in a caliper with non integrated parking brakes?
3. Do I need to open the bleeder valve to compress piston?

Why can't I push the caliper piston back?

The piston has to be pushed directly back into the caliper, any additional force on one side of it will cause it to bind up and not go back into the caliper. Try getting a big C-clamp and then using the plate from the old brake pad to push down directly over the piston.

What tool can be used to retract the pistons in a caliper with non integrated parking brakes?

A piston retraction tool, like that shown in Figure 15-2, is used to push the brake caliper piston back into its bore. The piston retraction tool shown in Figure 15-3 is used on rear disc brake systems that use a parking brake integral with the rear caliper.

Do I need to open the bleeder valve to compress piston?

You should know that if you don't open the bleeder valve, the brake fluid in the caliper will have a very high risk of getting contaminated. Assuming you compress the caliper piston without opening the bleeder valve, you also put the ABS sensor at a high risk of getting damaged.