Well, I could be wrong, but usually there is enough fluid in the master cylinder to last till your pads need changing. SOOOOOOOOooooo, maybe you have a leak, or maybe your pads are really close to needing changed and wonder about rotor thickness. Either way, BE real careful when you do a brake job, cause when you compress the pucks, that fluid has to go somewhere,... read all over your engine compartment and paint and brake fluid don't like each other along with whatever else it gets on.![]()