The brake lines that connect the master cylinder to the proportioning valve must be disconnected from the master cylinder. These two fittings can be a real pain to break loose. Start by applying plenty of WD-40 (or like substance). Using a flare wrench, try to break the fittings loose. If the flare wrench starts to spread open or the fittings have been rounded in the past, use a pair of vise grips to grip the fittings. Have a small container ready to catch the brake fluid that is stored in the master cylinder.