BMW Repair: 1984 318i Brakes, clutch slave, visible spot

Question
Hi Don:
My brakes grab fine and the car stops well, but then the pedal fades and drops while I wait in line at the stop on a hill.  Almost to the floor.  Pressure comes back when I pump the pedal.  Is this a failed master cylinder?  How do I differentiate between a failed master and a failure at a caliper?

Answer
If you are not using any brake fluid,I would check the linings on the rear to make sure that they are adjusted well.If after the adjustment and the fluid in the master cylinder is full and not leaking at any visible spot I would try bleeding the brakes starting with the right rear,left rear,clutch slave,right front,left front.Finally after all is done if the pedal still goes to the floor and you can pump and hold but creeps down then I would say it is the master cylinder.Make sure when bleeding that you don't bleed reservoir dry you don't want to have to start all over again.