Hello fellas. I just wondering how can you tell if the front brakes or rear brakes calipers are going bad? Or How can you tell if the master cylinder is going bad? I'm just confuse on how the brakes system works like for example, When do the rear brakes start braking like during stop and go or during hard braking?

Car Specificaitons:
2002 V6 3.8L Mustang
Mods: Magnaflow muffler
K&N Air Filter