hello, for now stop pushing the piston. They screw in with special tool. you can easily damage the caliper if you clamp too hard as they are complex inside due to E brake. Ther is a special tool for doing this or if you happen to have a spanner wrench OR have some way to grab the slots on the claiper piston and rotate it clockwise. below are directions. Line#1 explains

• Inspect the brake caliper bracket guide boot assembly for condition.
• Clean the brake pad hardware mating surfaces on the caliper bracket of any debris or corrosion.
• Inspect the brake pad retainer clips for condition and replace, if necessary.
• Inspect the piston boot for condition. Replace if damaged.

1. Retract the brake caliper piston (2) into the brake caliper bore. Use a suitable spanner type wrench and turn the piston clockwise until it bottoms out fully in the brake caliper (Mac® Tools DBC 25 C 2500 MA Disc Brake Caliper Tool Set, or equivalent).
2. Align the indents on the piston face to match the pin on the back of the inboard brake pads.
3. Install the brake pad retainers into the brake caliper bracket.
4. Install the inboard and outboard brake pads into the brake caliper bracket insuring that the pad with the metallic wear sensor is placed on the inboard side of the bracket.
5. Slide the caliper onto the bracket insuring that the bracket guide boots are not damaged.
6. Notice: Refer to Fastener Notice in Service Precautions. Insert the brake caliper bolts.

• • Tighten the brake caliper bolts to 34 Nm (25 ft. lbs.) .

1. Re-clamp the WSS harness onto the lower control arm.
2. Install the tire and wheel assembly.
3. Lower the vehicle. Refer to Lifting and Jacking the Vehicle.
4. With the engine OFF, gradually apply the brake pedal to approximately 2/3 of its travel distance.
5. Slowly release the brake pedal.
6. Wait 15 seconds, then repeat steps 10-11 until a firm brake pedal apply is obtained. This will properly seat the brake caliper pistons and brake pads.
7. Fill the brake master cylinder reservoir to the proper level. Refer to Master Cylinder Reservoir Filling.
8. Burnish the pads and rotors. Refer to Burnishing Pads and Rotors.