The fluid has to be going somewhere. If the master cylinder was empty, you need to bleed the whole system, not just the master cylinder. Start at right rear, move to left rear, then right front and left front. Make sure the master cylinder never completely drains or you'll have to start all over again. Bleed the cylinders. Calipers until there are no air bubbles in the fluid stream.
If the system continues to drain after bleeding, check the rubber brake hoses to the cylinders/calipers and the diverter and proportioning valves for leaks. Also check the steel lines for leaks. Thoroughly clean the brake booster(what the master is bolted to) and check the rear seal of the master cylinder for leaks. Also, with the engine running, loosen the master cylinder to booster bolts and listen carefully for air hissing. If heard, the booster is leaking and needs to be replaced and has most likely sucked the master cylinder piston seal out.
Saturday, September 17th, 2011 AT 8:27 PM