I have a 99 suburban and have a bad braking problem. I have searched and searched but found no answer. So first my pedal would go almost the the floor and would have little brakes. Replaced the rear shoes and a wheel cylinder and bleed them. Worked great for a week then slowly got worse and worse till my pedal went straight to the floor. One of the rear cylinder broke also I went ahead and replaced both of them. Worked great for about a week again then got worse and worse. Now I've got the same issue have to press the pedal almost all the way down to stop and I checked the fluid and the master cylinder is full. The fluid is a little dirty. I'm honestly lost on this and have no idea what it could be. Any help would be greatly appreciated