Pull Out the Caliper Piston
Since you have new, thicker pads, they won’t go into the caliper unless you push the piston down. (As the brake pads wear, the piston expands further to provide enough braking force each time you press the brake pedal.) You can do this with a special tool like the one shown here. Or you can use a simple C-clamp. However, always use an old brake shoe over the piston to avoid damaging the piston. It doesn’t take much force, but pull back slowly.

This procedure works well for front brakes. However, when changing the rear brakes, due to the emergency brake, a different special tool may be needed to compress the brake caliper. We explained this in another article. While some vehicles require a special tool, others, such as Mazdas equipped with electronic emergency braking, require a complex series of steps, including the ignition button, gas pedal, and brake switch. Not nearly as memorable as “up-up-down-left-right-right-BA” so I have to look for mine every time I work on the brakes. Find out if your machine uses a tool or a magic button combination.