Peculiar issue- Brakes- 1989

[DegosaithE]

Well i tried searching, i truly did but seems that either this is an easy fix or one that is unique to me.....

2 things:

I replaced my Brake Master Cylinder little less than a month ago due to first one leaking in the rear. Got brakes was fine..

Then my O2 sensor started popping off every now and then and without it i could hear the clanking so i kept just putting it on handtight since i was never at home but within 3 days i torqued it down with a wrench.... problem arises when i get above 4k rpm i can hear a soft clanking but nothing in terms of major discomfort, figure it could be just my exhaust since the clanking isnt necessarily loud or inconsistent, its just a soft slowly rising with rpm exhaust sound yet a little more distinguishable from the exhaust. Reminiscent of 02 completely off but not.... hard to explain

Here is my problem, about a week ago i lost all the pressure in my brake pedal, i push it down completely and it does stop making me think that either front or rear arent responding (my guess is front since the stopping seems less powerful than that of a front). I figure hey, might be need new pads although i expected some sort of warning rather than all pressure loss, plus kind of self assured on new master cylinder since there is no decrease in fluid levels and im not leaking; plus when installing it i did so correctly although i overbled it to make sure there were absolutely no bubbles. Right now im sittin in my garage with my wheels off staring at my pads which arent completely worn (not to a point of the metal warning piece touching the disc) and wondering if im correct in assuming its the pads. I figure i will bleed the brakes and find out if there is leakage, but i need another person for that thus im gonna hafta do it tomorrow.

At a moments glance, what do you guys think the problem might be? Week ago working fine, then for a day or two it got really soggy then its completely gone. I did the test of turning the car off and pumping to see if there is pressure and there is plenty as soon as car is off, but when i turn it on the resistance is completely gone. This means from what i read that master cylinder is doing its job and i might have a leak somewhere... although i can not detect it after inspecting the front hoses.
Modified by DegosaithE at 1:26 PM 1/5/2010

[Cone Junky]

First off, don't assume the new part is a good part. Your symptoms describe a hydraulic leak. So there is either an obvius external leak or an internal leak (master cylinder).Unless they fell out, brake pads should not cause the pedal to go soft.Definitely do a thorough visual inspection, then I would raise all four wheels off the ground. Have someone press on the brake pedal while you try to spin each wheel. This may reveal a dead or leaking caliper if some of the wheels lock and others still spin.Otherwise it looks like you need to return the master cylinder for warranty and start over.

The exhaust leak will have to be left to someone who can actually hear it and help you pinpoint it.