Use a C clamp to push the piston out of the way to remove and also to place back on rotor.
use a c-clamp and push the piston in that way. style c-clamp i sue http://www-ece.rice.edu/~jdw/figs/c_clamp_2.jpg
I have a 2004 TSX and learned the hard way how to change the rear brakes and had to buy a rebuilt caliper for my mistake. Most brake calipers compress with a simple C-clamp to make room for the larger/newer brake pads. The rear brakes on a TSX are different and you'll notice they have a couple of grooves on the caliper piston. They make a tool that is sold at AutoZone that allows you to compress the caliper piston by rotating it clockwise back into the piston. (It looks like a metal cube with metal prongs sticking out) I also recommend using brake grease on the exposed caliper piston boot prior to compressing it as this will allow the piston to rotate without damaging the boot. Don't forget to bleed the brakes afterward since rotating the piston will likely allow some air into the brake caliper.
If I recall, a g6 has disc brakes front and rear, and are largely identical to the disc brake systems on most other cars, except for one thing; the rear g6 calipers cannot be compressed manually to fit in the new pads. A special tool is required to compress them. If you don't have that tool, you can't compress the caliper piston. If you can't compress that caliper piston, you can't fit in the new pads. Ask at an auto-parts store for a "Disk Brake Caliper Tool" set. Should be less than 30.00usd depending on the brand they carry. Note: The g6 *front* brake caliper pistons compress manually, no special tools needed.
Remove the wheels. Remove the Caliper off the Rotor by removing the two (top and bottom) bolts that hold it on. (14mm i think) Remove the old pads. Compress the piston all the way back into the caliper to provide space for the new pads. (Checker/O'Reilly Auto sells a cube like tool that fits onto a 1/2" ratchet to compress the piston, or borrow the compression tool from Auto Zone.) Put the tabs and new pads in. Replace the caliper mounting bolts and attach the caliper back onto the rotor. After you're done make sure you press the brake padel in all the way and Slowly let it out. You're making sure the caliper piston is correctly seated against the pads and they'll self adjust.
cheap caliper compressor from auto parts store, 1 size fits all.
caliper piston does not retract with moderate C-clamp pressure - not willing to force it
The brake pads on a 2007 Volkswagen Passat are replaced by jacking the vehicle up, removing the wheels, and unbolting the calipers. The pads can then be removed from the calipers, the caliper piston compressed, and new pads installed.
19mm deep socket for wheelnuts, 7mm Allen wrench to remove caliper bolts, 8" c clamp to push piston back into caliper housing
19mm socket removes the front tire. 9mm allen head removes the caliper from the caliper mount. c-clamp resets the calipers piston. straight screwdriver removes pads from caliper. install new pads and put back together.
you can buy a tool from car shop just for the job. you place it between the brake piston and in the caliper and twist pushes pistonsback and lets you fit new pads costs about £20.00 but worth it hope this helps
You need a special tool, which is pretty commonly available. It is a disk with a 3/8" square hole in the center, and two pegs on one side. The pegs fit into corresponding slots on the piston, and you ratchet the pistons back into their seats. I can't remember which direction they turn, but I think it is clockwise.