I've been fighting brake problems with the dually. The pedal went to the floor last Friday. I checked the fluid and the front reservoir was low and the master cylinder was leaking. I replaced the master cylinder and turned the rotors since the truck has had a vibration when braking. It has brakes now but the vibration is just as bad. I noticed that the vibration was gone when the pedal was going to the floor. Could it be that the front reservoir is for the rear brakes and the vibration was gone since there were no rear brakes? I'm thinking that the rear brake drums need turning too.