No, swallowing saliva does not break fast, even if its a lot. Swallowing mucus does not break fast either: It is haraam to swallow mucus whether one is fasting or not, because it is considered to be dirty and it may carry diseases produced by the body. But it does not break the fast if a fasting person swallows it, because it does not come from blood and swallowing it is not regarded as food or drink. If he swallows it after it reaches the mouth, it does not break the fast. From the words of Shaykh Muhammad ibn ‘Uthaymeen, may Allaah have mercy on him. See al-Sharh al-Mumti’, 6/428.