Brakes on 96 sunfire

I have a 96 Sunfire 2.4L w/98k miles. Recently my brakes started acting up. The pedal goes way down and is hard at the bottom. The brakes work but I'm not sure about stopping fast if I had to. The pads and shoes are all good. I checked the fluid and it was low so I added some but this did not help. Even pumping the pedal does not bring the pressure up. Is it possible that the low fluid level allowed air into the system and they need to be bled or is it more likely a master cylinder failure or booster failure? Thanks in advance, Guy

The master cylinder is probably going bad but air in the the system is a good possibility. I would bleed the brakes to see what happens but you may have to bleed the master cylinder as well. Finally, check the vacuum line to the booster. There is a one way check valve in the end if it went bad it may prevent any vacuum assist to the booster.

Thank you once again.