aight i have a 95 ls and when i push the brakes they work semi good .. but when i come to a stop and hold the brake pedal down it slowly travels to the floor ... does that mean i have air and just need to bleed the lines or does it mean my master cylinder is going bad ... because i heard both .... and if its the master cylinder how do i check that ... i have new pads and rotors to put on but dont want to until i figure out why my brake pedal might be doign this ... thanks