I have a 2006 Scion Tc. I started having brake issues about 3 months ago. The back brakes were at little squeaky, then eventually in turned into a grinding. I was backing out of my driveway when i heard a loud grind and then a thud. The grinding stopped but I noticed my car was a lot harder to stop, meaning the pedal was very soft and almost going to the floor. I didn't have the time or the money to fix them so I kept driving on it for about another week when my front pads started grinding. By this time my pedal was going all the way to the floor. I finally changed the front and rear pads. No more grinding but the pedal was still going to the floor. So after some research I decided to replace the master cylinder. I didn't help one bit. I was looking into replacing the brake booster but I decided to take it to a mechanic. They inspected the entire braking system an decided that it was the master cylinder even after I told them I had already replaced it. They had my car all day and called me back after replacing the master cylinder and said it is still going to the floor. They said I have power brakes and the brake booster makes it easier for the pedal to move, that's why when the car is off you cant move the pedal very easily. So I know it's not the booster, but I have no idea what else it could be. They said they are going to keep it a few days to see if they can figure out what it could be. Any suggestions as to what it could be would be appreciated.

I should add that when I changed the rear pads I noticed there was no inside pad on the drivers side. I am assuming that is what the loud thud sound that I heard and both front a rear pad were horribly unevenly worn. All most no pad on the inside and hardly any wear on the outside. I know that has to do with the caliper pins moving or not but the mechanic didn't even mention the pins.

 

It sounds like there may be a leak in the brake line or a problem with the ABS system, causing the loss of pressure in the braking system despite replacing the master cylinder. Try to inspect your brake system for any visible signs of damage or leaks. Look for any brake fluid that may be leaking or any worn out brake components, like calipers, pads, or rotors or best to take it to a mechanic.