My friend has a 2005 Peugeot 206. He brought it by for me to advise him on the brakes, and when I test drove it the brakes were soft and spongy. He then took it to a mechanic, and when he picked the car up the guy told him the master cylinder needs replacing. Upon test driving the car, my friend found the brakes were now worse to the point of being almost useless, and there was now a hissing noise whenever the brake pedal was pressed.
So he brought it to me again and left it with me to change the brake fluid / bleed the brakes. I checked the reservoir which was full. I lightly pressed on the brake and it did not float down to the floor. Pumping the brake didn't improve the softness.
So I went ahead and bleed the brakes. Front wheel drive, so I did it in an X pattern ( FL, RR, FR, RL ). The fluid clearly hadn't been changed in a long time, it came out a brownish color and seemed to have allot of tiny specs of rust floating in it. There were allot of tiny bubbles, and one bleeder seemed to have a huge amount of air. I coated the bleeder threads and tube connection with silicon grease to make sure air wouldn't get in from the outside, the tube was curved up and the other end was submerged in fluid, so I'm fairly certain the air I saw came out of the brake lines.
Anyways, after finishing I took it for a test drive. At first the brakes still seemed a bit soft, but they firmed up after some use. I got going fast and was able to stop fairly quick, and the ABS seemed to be working correctly.
However, I still hear the hissing / pishing noise when I push down the pedal, and on gentle stops the brakes feel a bit weak, although not really mushy anymore. The front break pads where replaced about six months ago and look good.
So, what could the mechanic have done that would cause that pishing sound when the brake is depressed, and taking into consideration what I've done so far, what else needs to be done, tested?