As someone else mentioned, the clips must be installed properly and if they are not you will have an eratic pedal and sometime even a rattle.
Another posibility as others have mentioned is air in the system and you should bleed the system carefull and thoroughly to make sure all the air is expelled.
Still another posibility (but not nearly as likely) is that one of the cups in the master cylinder has collapsed. This can happen if the brake fluid is trashy from collapsing the pistons on the calipers, especially if you push them in very rapidly. This is a good reason (among many others) to change the brake fluid from time to time. If one of the cups in the master has collapsed, the master needs to be replaced.
