A disc brake piston tool is great to have when doing your own brake work. Over time, as your brake pads and brake rotors wear, the brake piston in your caliper will move farther and farther out of its bore. This helps maintain the braking function, feel and effort as parts wear down.
When it comes time to replace your brake pads and rotors, the brake piston must be pushed back into its bore before the new pads and rotors will fit. This is where the disc brake piston tool comes in. It allows you to easily exert a large enough force on the brake piston, to push it back into its bore.
Using a disc brake piston tool is easy:
Once the caliper has been retracted back into its bore, you can move on to installing your new brake pads and rotors, which will now easily slide over each other. Be sure to press the brake pedal a few times before moving the car, to re-seat the pads against the rotors.