1998 concorde brakes

since winter began i have been hearing air sound (like air deflating from tires) when i depress my brakes. it sometimes goes away when the car warms, but not always. at times as well, the brake pedal is difficult to depress. it then improves again. i have noticed vibration through the steering wheel when on the interstate. occassionally, lately i have also noticed that the front brakes feel as if they are engaging slightly without depressing the brake pedal. for instance, the car does not move when in gear and idling) the front brakes then smell as if the brakepads are overheating (burnt smell on front). i replaced the pads and rotors this week with no improvement. any ideas? any ways to test without replacing power booster, etc. thanks for any help.

Chances are the brake booster diaphram is ruptured and leaking vacuum causing the hissing sound, you will most like have to replace the booster. if the pads are dragging thet usually indicates the slides (where the mounting bolts go through on the caliper are binding and not allowing the caliper to slide or "float" sometimes they can be freed up by removing them and applying some grease to the slides and reinstalling. It is also possible the caliper piston is binding and not retracting enough to allow the brakes to totally release, if that is the case the caliper must be rebuilt or replaced.