Cannot fit caliper w/new pads on rotor(rear brakes)

hi Ed.
It's nearly time to install the new brake pads. But there's one more step to complete before you can do that. You have to manually retract the caliper piston.
If you look at the inside of the caliper you'll see a cylindrical piston coming out -- this part pushes on the inboard side of the brake pad. You'll see that it has adjusted itself to match your worn-out pads, so you'll need to reset the piston to its original position before the caliper, along with your new (and thicker) brake pads, will fit over the rotor.

Before you reset the caliper piston, it's a good idea to remove the cap that covers the brake fluid reservoir. If you don't, you'll be fighting against a significant amount of brake fluid pressure.
Now that the reservoir cap is removed, this is the part where you'll need that C-clamp. Place the end with the screw on it against the piston. You can use a small piece of wood to protect the surface of the piston, if you choose. As you turn the screw, the clamp will increase the pressure on the piston. Keep tightening it until you're able to slip the new pads into the caliper and fit the caliper and the new pads over the brake rotor.
If you find that the piston isn't properly retracting, don't force it. You may have a caliper that's been designed with a piston that slowly turns as it extends. If that's the case, then you'll need a special tool to thread the piston back into the caliper. A brake caliper tool -- a tool specifically designed to retract this type of brake caliper piston -- is available for purchase at most auto parts stores. If you can't find one there, then you can order the tool online -- or if you're really lucky, maybe your neighbor will have one that you can borrow for the afternoon.
Once the brake caliper piston has been fully retracted, you can re-cap the brake fluid reservoir. It's not a good idea to leave the cap off of your brake fluid reservoir for any longer than is absolutely necessary. Debris or even water may find its way into your brake's hydraulic system. Brake fluid is hygroscopic, which means that it absorbs and retains water. Water in the brake lines leads to serious safety concerns and more complex repairs than the relatively simple pad replacement that you're finishing up with right now.
Installing the new brake pads themselves is just a simple matter of slipping the new pads into the slots where you found the old ones. If they don't easily fit in with your hands, you may want to tap them in gently with a hammer or rubber mallet. Then, replace the pins or bolts that held them in place and you're nearly done.
Next, move the caliper back into position on the brake rotor. Make sure it fits snugly, and tighten the bolts that hold the caliper in place. Make sure everything is back in place and then give the brake pedal a few pumps from inside your car just to make sure the pedal feels right to you. It may take several pumps of the pedal to get the brakes to properly seat themselves into their new position.
The rest of the brake repair is easy. Put the wheel back on, tighten the lug nuts, remove the jack stands and lower the car to the ground using your jack. It's just like changing a tire. Remember to fully tighten (and properly torque) the lug nuts once you have the vehicle back on the ground.
Also, don't forget to test drive the car to make sure that your brake work was successful. Fixing brakes is one thing; making sure they work properly is another.

if you need more info go to this link.
there is youtube videos showing you how to do it.

how do you open brake caliper so new pads fit Google Search

Depending on vehicle. Find level ground and park there. Put chocks in front and behind wheels not being lifted. Loosen lugs, jack up vehicle, set jack stands, lower vehicle on jack stands, remove lugs and wheel. Open hood remove brake fluid cap. Remove two bolts holding caliper, pull caliper off rotor disc and bracket, remove pads, place a used pad in front of caliper piston, use a c clamp to push caliper piston in caliper, remove c clamp and old pad, hang caliper up, remove 2 bolts holding caliper bracket, remove bracket, remove rotor, install new rotor, install caliper bracket, install new pads, install caliper, repeat this on other side, put cap back on brake fluid tank, remove bleeder fittings and keep pressing brake pedal until an even flow of brake fluid sprays out. Install bleeder fitting. Make sure brake fluid doesnt get on paint and is contained and disposed of correctly, top off fluid install wheels and raise car up remove jack stands, lower car and break in new pads

Remove the caliper mounting bolts and remove the caliper. Replace brake pads as necessary. Special tool is required to retract caliper piston to fit over new pads. (see picture below)
Retract piston in caliper using special tool to rotate clockwise and make sure the notch in the piston is aligned properly so the tab on the inner pad will fit in properly.
Reinstall caliper assembly and caliper mounting bolts.

you should'nt have any tension on the parking brake,unless it's on. check the parking brake to insure that it's in the off position. chock" the rear wheels,to make sure the car does'nt roll while you're jacking it up and "always use jackstands,do not trust your jack" does your brake caliper piston have a + on it?it will be on the brake caliper piston itself, if so,then you need to back the brake caliper piston back in by turning it counterclockwise,auto parts stores sell a special tool to back the brake calipers back into place, i've always used a straight screwdriver,to turn the piston counterclockwise some do turn clockwise though to retract the brake piston. a simple call to the auto parts store where you're purchasing the brakes will tell you which way the piston will need to be retracted.other wise,it's a simple brake replacement,just push the brake caliper cylinder with a "C" clamp to retract the brake caliper, also,if you are replacing brake rotors,purchase the brake kleen to spray on the new brake rotors when you replace those.they have a clear film on them,you'll need to remove that film to insure no future issues with the brake rotors.simply spray the front and back of the brake rotors with this spray to remove the protective "film"and as always,thank you,for choosing fixya.com!

yes, you can rent one from Auto Zone, Advanced Auto Parts, etc.

Remove brake fluid from the master cylinder brake fluid reservoir until the reservoir is approximately 1/2 full. Discard the removed fluid.

1. Raise and safely support the front of the vehicle. Remove the front wheels.
   

1. Remove or disconnect the following:
2. Front brake caliper guide pin bolts
   

• Brake caliper by slowly sliding it up and off the adapter and brake rotor. Support the caliper out of the way with a strong piece of wire. Do not let the caliper hang by the brake hose or damage to the brake hose will result.
  

1. If necessary, compress the caliper piston into the bore using a C-clamp. Insert a suitable piece of wood between the C-clamp and caliper piston to protect the piston.
2. Outboard disc brake pad from the caliper by prying the brake pad retaining clip over the raised area on the caliper. Slide the brake pad down and off the caliper.
   

• Inboard disc brake pad from the caliper by pulling the brake pad away from the caliper piston until the retaining clip on the pad is free from the caliper piston cavity
  

To install:

1. Be sure the caliper piston has been completely retracted into the piston bore of the caliper assembly. This is required when installing the brake caliper equipped with new brake pads.
   
2. If equipped, remove the protective paper from the noise suppression gaskets on the new disc brake pads.
   
3. Install or connect the following:
   
   • New inboard disc brake pad into the caliper piston by pressing the pad firmly into the cavity of the caliper piston. Be sure the new inboard brake pad is seated squarely against the face of the brake caliper piston.
     
   • Outboard disc brake pad by sliding it onto the caliper assembly
     
   • Brake caliper assembly over the brake rotor and onto the steering knuckle adapter
     
   • Caliper guide pin bolts and torque to: 35 ft. lbs. (47 Nm) on 2002–04 models or 26 ft. lbs. (35 Nm) on 2005 models
     
   • Front. Apply the brake pedal several times until a firm pedal is obtained.
     
4. Check the fluid level in the master cylinder and add fluid as necessary. Road-test the vehicle.
   

For the rotors:

1. Remove brake fluid from the master cylinder brake fluid reservoir until the reservoir is approximately 1/2 full. Discard the removed fluid.
   
2. Raise and safely support the front of the vehicle. Remove the front wheels.
   

1. Remove or disconnect the following:
2. Front brake caliper guide pin bolts
   

• Brake caliper by slowly sliding it up and off the adapter and brake rotor. Support the caliper out of the way with a strong piece of wire. Do not let the caliper hang by the brake hose or damage to the brake hose will result.
  

1. If necessary, compress the caliper piston into the bore using a C-clamp. Insert a suitable piece of wood between the C-clamp and caliper piston to protect the piston.
2. Outboard disc brake pad from the caliper by prying the brake pad retaining clip over the raised area on the caliper. Slide the brake pad down and off the caliper.
   

• Inboard disc brake pad from the caliper by pulling the brake pad away from the caliper piston until the retaining clip on the pad is free from the caliper piston cavity
  

To install:

1. Be sure the caliper piston has been completely retracted into the piston bore of the caliper assembly. This is required when installing the brake caliper equipped with new brake pads.
   
2. If equipped, remove the protective paper from the noise suppression gaskets on the new disc brake pads.
   
3. Install or connect the following:
   
   • New inboard disc brake pad into the caliper piston by pressing the pad firmly into the cavity of the caliper piston. Be sure the new inboard brake pad is seated squarely against the face of the brake caliper piston.
     
   • Outboard disc brake pad by sliding it onto the caliper assembly
     
   • Brake caliper assembly over the brake rotor and onto the steering knuckle adapter
     
   • Caliper guide pin bolts and torque to: 35 ft. lbs. (47 Nm) on 2002–04 models or 26 ft. lbs. (35 Nm) on 2005 models
     
   • Front. Apply the brake pedal several times until a firm pedal is obtained.
     
4. Check the fluid level in the master cylinder and add fluid as necessary. Road-test the vehicle.
   

u have to turn the piston clockwise as you compress it.

Removal & Installation

1. Before servicing the vehicle, refer to the Precautions section.
   
2. Remove or disconnect the following:
   
   • Negative battery cable
     
   • Front wheels
     
3. Place a C-clamp over the caliper as illustrated, place a screw drive head against the outboard pad and hook against the rear of the caliper. Slowly tighten the screw drive and retract the caliper pistons into their bores and breaking the outboard brake pad from the caliper fingers.
   
4. Once the pad is free, slide the caliper in on the guides to provide clearance between the rotor and inboard pad.
   
5. Place an appropriate prytool through the center opening in the top of the caliper behind the inboard pad between the pistons using care not to contact the piston boots. Pry the pad to free it from the pistons.
   
6. Remove the two caliper guide pin bolts and position the caliper aside. Remove the brake pads.
   

Place a C-clamp over the caliper as illustrated


View of the caliper guide pins and boots (1), anti-rattle clips (2), brake rotor (3), outboard pad (4), caliper adapter (5) and inboard pad (6)

To install:

1. Completely compress the caliper pistons
   
2. Install or connect the following:
   
   • Brake pads with anti-rattle clips onto the adapter
     
   • Caliper and align the guide pin bolt holes with the guide pins. Install the pin bolts and tighten to 32 ft. lbs. (43 Nm).
     
   • Banjo bolt with new washers on each side of the hose fitting and tighten to 35 ft. lbs. (47 Nm)
     
   • Wheels
     
   • Negative battery cable
     
3. Check and adjust the brake system fluid level and road test the vehicle.
   

Try tapping around the rotor hat (the area that actually fits over the hub, where the lug bolt holes are) with a hammer. That usually will loosen up a rotor that's stuck due to heat, dust, etc. As for compressing the rear piston, they're a screw-in design, not a compression design like the front calipers. You need a piston retracting set (you can borrow them from AutoZone), and with that you can screw the pistons into the calipers. After removing the reservoir cap underhood, screw them all the way in so that you have ample clearance for the new pads over the new rotors, then pump the brakes a few times before you hit the road (put the reservoir cap back on first).

A big pair of channel locks will collaspe the caliper but it does take some muscle or you can release the brake line nut and releave the pressure but then you would have to bleed the brakes.