Probably beating a dead horse but here goes. For quite some time my brakes have been spongy. The car stops ok but I think the pedal travels too far before starting to grab. I've bled all the brakes in the past with no improvement. Last weekend I replaced both rear calipers and bled just the raer brakes this time. If anything the brakes are slightly worse than before. Between the two calipers I've probably pumped out a small jelly jar of new brake fluid. Is that enough to clear the lines of air? Is it possible my master cylinder is bypassing fluid internally?
You probably do not have the rear caliper e-brake section adjusted properly. There are e-brake levers on the back of the calipers, these often need to be manually adjusted in order to get the rear brake pads right out against the rotors. If not adjusted properly, you end up with a low pedal as you are using up a lot of pedal travel just to get the rear pads out to the rear rotors.
Do this: Take the rear wheels off, use an 11/16" wrench to turn the e-brake lever "towards" the e-brake cable that is attached to it. You should see the caliper piston move out of its bore. Pull the lever back to it's "off " position, and watch the piston.....if it moves back into it's bore, then you will need to manually hold the piston out when you return the lever. Turn the lever again, and stick the tip of a screwdriver into a groove that will be exposed on the piston. Hold the piston out....while you move the lever back. Keep doing this until you can only move the e-brake lever about 1/2" to 1" of play.
Repeat on the other side, and then see how the brake pedal feels. You should also test your e-brake from the pedal in the car. Put it on, then release it and make sure that both calipers are released at the rear. If not, you probably have some seized e-brake cables. If having a park brake is not a big issue for you (auto trans) then just manually release the brakes at the rear, and don't use the park brake again.
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