I am replacing my break pads and can't get the piston to press back in the caliper on my 1995 merc sable.

You are talking about the piston being pushed out? #1. Put a piece of wood in the caliper and push the brake pedal again.. remove the piston all the way. clean the caliper bore, replace the seal(caliper rebuild kit usually really cheap) carefully reinstall the piston.. sounds like it is either "cocked and stuck or the caliper has a ring of rust at the top of the bore. either way clean and reinstall the piston. possibilty #2. Take a "C" Clamp and force the piston back in.. if you do this take an old pad and put it between the piston and clamp to protect the poston.

The caliper is bolted on by sliding pins that allow the caliper to adjust itself. I would assume the sliding pins are stuck. The bolts slide inside the carrier that holds the calipers.

Remove & Replace the Brake Pads

• Loosen lug nuts from the front wheels with the ratchet and socket, but do not remove them.
• Raise the front of the vehicle using the floor jack and secure it with jack stands.
• Remove the lug nuts from the wheels and pull the wheels from the vehicle.
• Look on the rear of the brake caliper and locate the caliper bolts, one upper and one lower.
• Loosen and remove the upper and lower caliper bolts using the ratchet and socket.
• Pull the caliper from the brake assembly, exposing the brake pads, and hang the caliper from a suspension component, using the bungee strap. Do not allow the caliper to hang by its hose, as this may cause damage.
• Grasp the inner and outer brake pads and pull them from the brake assembly. Take note of how they were positioned, as the new brake pads must be placed in the same fashion.
• Place the new brake pads on the brake assembly in the same position the old ones were.
• Position the c-clamp over the caliper so the screw portion is contacting the the caliper's piston--the metal cylindrical object inside the caliper--and the fixed portion of the clamp is contacting the rear of the caliper.
• Tighten the c-clamp until the caliper's piston is fully pressed into the calipers body. The top of the piston is even with the caliper body when fully pressed in.
• Loosen the c-clamp and remove it from the caliper.
• Place the caliper over the new brake pads and hand-tighten the upper and lower caliper bolts.
• Tighten the upper and lower caliper bolts to 26-foot pounds, using the torque wrench and a socket.
• Repeat Steps 4 through 13 for the brake pads on the other side of the vehicle.
• Place the wheels back on the vehicle and hand-tighten the lug nuts.
• Remove the jack stands from under the vehicle and gently lower it to the ground.
• Tighten the lug nuts to 100-foot pounds using the torque wrench and a socket.
• Press and release the brake pedal repeatedly until it feels firm.

Take the rotor off and check the ebrake. If the rotor is hard to get off then the ebrake is holding it on and is most likely your problem. It won't be your master cylinder or proportioning valve because it is only affecting one side. Any questions feel free to email me at [email protected]

For front brake pads replacement you need only usually wrench set, inclusive 7 mm allen key also.
But for rear brake pads replacement you need obligatory a special caliper piston pressing tool, in order to press back rear caliper piston with parking brake automatic adjustment!!!
For front brake pads. First you must verify yours front brake disc diameter: 280 mm or 288 mm. After that you can buy the brake pads (with wear sensor). For change front brake pads you must raise vehicle, remove wheels, extract the retaining spring of the caliper, and remove the caliper as follow:
1. Do not disconnect the brake hose from the caliper, and do not allow the caliper to hang by the brake hose!
2. Remove top and bottom caps (on back side of the caliper) for access to guide pins, then unbolt and remove them from the brake carrier. Remove the caliper.
3. Now you must thoroughly clean the brake calipers (free of grease).
4. Remove outer brake pad from brake carrier.
5. Pull inner brake pad out of brake caliper piston.
6. Check up the brake fluid level on the reservor, and emptying if neccessary!
7. Push piston back into brake caliper housing.
8. Install inner brake pad (with expanding spring) in brake caliper piston. (Arrow marked on pad - if exist, must point in direction of brake disc rotation when vehicle is moving forward).
9. Install outer brake pad into brake carrier.
10. Bolt brake caliper housing to brake carrier using two guide pins. Tightening torque is 25 Nm.
11. Install both caps.
12. Insert retaining spring into brake caliper housing. Important: Depress the brake pedal firmly several times while the car is stationary so that the brake pads adjust to their normal operating positions!!! Check brake fluid level and top up if neccessary!!!

No do not use a c clamp to press the rotor back in unless you plan on breaking your clamp !!!! On that particular model of (Tiburon) the calipers screw back in.

Remove the wheel, remove the 2 bolts holding on the caliper to the caliper carrier. You will need a large C-Clamp or a cailper piston tool. Place an old brake pad against the piston in the caliper and use the C-Clamp to push the brake pad against the piston to collapses the piston into the caliper. Also open the master cylinder cap and place a towel around the area to catch any brake fluid that would come out of the master cylinder as you collapes the piston, this is normal, but doesn't always happen, depending on the level of fluid in the master cylinder. Install the new pads and reinstall the caliper and wheel. Make sure you pump the brake pedal a few times before you take off, to get the pads against the rotor.

break lug nuts loose
jack up car place stand under car
remove lug nuts and wheel
remove brake caliper
take out pad on outside of caliper
place a brake caliper press on pad next to piston of caliper and compress piston back in caliper
remove press and replace pads
reinstall caliper and wheels set car down
REMBER TO GET IN AND PUMP BRAKE PEDAL A COUPLE TIMES OR YOU WILL NOT HAVE ANY BRAKES WHEN YOU MOVE YOUR CAR!!!!!!
check fluid in master cylinder
take your time

When you replace the pads you have to retract the pistons into the bore. As the pads wear they stay extended from the brake caliper. The new thinkness of the pads will not allow the pads the slip over the rotors until you retract the pistons. Your pistons may be the type that have to be turned back into the bore.Good luck.

actually theres a special tool that connects to an air pump hose that expands the caliper back but you can use a vise if your very careful with pressing it back or locking clamp that you can use like a vise but this requires hand presure loosen bleed screw then use the vise