Brake Problems

One other thing, when I press the brake pedal I hear what sounds like air escaping. I'm working alone so I can't be pressing the pedal and looking under the hood at the same time.

To bleed the brakes on the rear, you start with the right rear. Pump up the brakes with the bleeder closed, even tho pressure may not build up and hold the break pedal on the last pump. So obviously you are going to need 2 people to do this. Then open the bleeder valve and close it. Eventually you will work the air out. Repeat this process until all air is pushed out. Try to avoid pressing the brake pedal to the floor while pumping up the brakes.

That air sound is probably the brake assist releasing its vacuum.

Is there any sort of proportioning valve in the system or is it all controlled through the abs module?

Okay. I've replaced the frozen calipers on rear left, brake hose on rear left, vacuum booster under the hood (real pain in the wrench!) but now, different yet related problem. I have bled the lines, no air at all in the system. When I have vehicle off, the brake pedal is firm. Once I start it, the brake pedal goes to the floor. Any suggestions/ideas?

If for any reason the master cylinder had run dry, would mean that air had ben pumped down from the master cylinder threw the ABS unit. So the only way to bleed out the ABS unit would be to have a shop to do this as it requires a computer program to operate the valves in the unit to bleed the air out.

Also if this was not the case with the ABS unit, I would suspect the master cylinder would need replacing. When replacing a master, it needs to be bench bled before installing.