Classic/Antique Car Repair: power brakes with drums on 1966 mustang convertible, rear shoes, power brakes

Question
I have never had the power brakes on a classic. On my new 66 when I press down on the pedal it slows down reel good but at the end of the stop it doesn't want to stop, I have to press hard. The brakes do not pull either way when braking. Should I bleed them or Check for shoe adjustment or do you think the booster might have a seal problem? The fluid level is good with no leaks. Thank you, Eric

Answer
  Everything in me tells me to tell you your master cylinder has gone out and it bleeding back through on itself. Replace it and you will be done.
  BUT, let's check a few inexpensive things first. Check your rear brake shoes and make sure they are adjusted out as far as possible. This can also be checked by partially applying the parking brake and seeing if that 'fixes' the problem. If so, you are simply over-ranging the ability of the two drum systems to work together. Keeping the rear shoes tight will keep this in check.

  Also, if your master cylinder is leaking, it will be between it and the power booster on the bottom side. The leak may be very slight.

  It does not sound like a booster seal problem or air in the lines from what you have described.