Replaced right rear caliper

Was brake system bleed?

Do you have four steel lines leaving the master cylinder? Did you pedal-bleed the system with a helper, and did he push the pedal all the way to the floor?

What do you mean by "no pressure"? If you mean the pedal can be easily pushed to the floor with no resistance, the master cylinder was likely damaged and is leaking internally.

If you mean there is no fluid pressure to the right rear brake, and there are four lines from the master cylinder, that system uses a valve in the master cylinder to block fluid flow. That valve must be reset before fluid will flow to the right rear or the left front.

Bleed the system properly and I bet you'll have brakes

Silly me. Sorry for forgetting this important detail, but if you have the parking brake lever built into the caliper, it is extremely difficult to get the air out of the hollow piston. It is hollow because that's where the screw and actuator lives for the parking brake. You might need to stand the caliper up so the hole for the brake hose is straight up, then fill it with fluid. We used a squirt bottle with a built-in plastic straw but an eye dropper will work too.

Once it's back on the car, you must adjust the piston out by working the parking brake. The piston will not be forced out by pumping the service brake pedal. Well, actually it will, but it will go back in when you release the pedal. The only way to get it out is by activating the parking brake. If it doesn't work or you're afraid a cable might be rusted tight, use a large channel-lock pliers to work the lever by hand. You shouldn't have to stroke the lever more than four to six times. Until the piston comes out and contacts the pads, there won't be a good pedal.