Replaced rear breaks, 2007 spectra, breal pedel is solf, goes to the floor. how do I firm up break pedel, never broke any lines.

Have you checked the master cylinder for leaks and around the brake booster? You may have a bad brake light switch.

Sounds to me that your power brake booster is bad or your portioning valve might not be working correctly there is a button on the portioning valve that can be pressed try that or replace it!

you have a leaky brake booster from the sounds of it

Do you have rusted out brake tubing or a blown
brake flex hose
Obviously & rarely do brakes go to the floor
Can't see the issue from the internet

Try pumping the brake pedel. If the pedel travel comes up, the rear brakes need to be adjusted. If the pedel does not come up, it could be a bad master cylinder or a broken brake line.

The rear brakes on the Spectra will always engage less than the front brakes. If you have to push hard on the brake pedal then you probably have air in the brake lines from the last brake pad replacement. The brakes need to be bled with this method: Use 1/8 inch 2 foot long hose from parts store and attach from bleeder valve ball on the brake caliper to a bottle partially filled with brake fluid. End of hose should be submerged in bottle. With second person holding brake pedal to floor, slowly turn bleeder valve counter clockwise (loosen tiny bit) with wrench and watch for dirty brake fluid to create bubbles in the bottle. When bubbles start, quickly tighten bleeder valve back to tight. Second person lifts foot while valve is tight and then pushes pedal to floor again and THEN you again open bleeder valve slowly turning counter clockwise and watch for bubbles. Repeat until no more bubbles can be created in the bottle where the hose is submerged. Move to next caliper and repeat. For a firm brake pedal you will need to repeat this on all four calipers. My 2003 Kia's rear brake pads "fell apart" and never wore out in 190000 miles because they do not get used. The braking power is primarily in the front disk brakes on this model. Removing and replacing the rear drum brake linings did not even require me to bleed the brake lines. They weren't that tight before or after the replacement procedure.

air in brake lines or faulty master cylinder

you need to hold in the metering valve.when you bleed the front brakes.long as the valve closed off you wont be able to bleed front brakes.better to get extra help.hard to bleed by your self .

try bleeding the brakes as a system. start by making sure the master cylinder is full. then have a Friend step on the brakes and release 3-5 times. the last one they should hold as you break lose the bleeder on the passenger side rear, then do the driver side rear ,(check fluid) next passenger front and then the driver side front do each wheel until you don't see any or hear any air, thats the way i have always bleed brake systems. hope this helps

refill the master cylinder with the proper break fluid then jst bleed them again and you should be good to go