[bonesbmx]

hey guys
i was wondering how does a master cylinder fail? today on i push on the pedal and it goes to the floor when i pump it its fine and firm but every so often it pushes down to floor again. i happen to have new pads drums and brake cylinders for both front and back so i installed them. pedal is firmer but still every so often goes to floor i gotta pump them to get it back. i took to brake shop they blead lines and told me the master is going. just wanted to hear from you guys first. everything is new even the lines so it would have to be either cylinder or booster right?
thanks