Classic/Antique Car Repair: power drum brake problem,, ashville nc, power brakes

Question
QUESTION: I have a 66 mustang coupe with drum brakes.  I put power brakes on it and now when the brake pedal is depressed you press the pedal and hold it, it is somewhat hard then it goes down and stops the car very well.  It is so aggravating when you have to stop you may throw everyone forward in the car.  You go from no stop to full stop.  I have more brakes than I have ever had.  I replaced the booster thinking it was it but no different.  I checked the vacuum and I got 19 inches.  I checked all the lines and they are good.  All the brakes are new.  All new wheel cylinders, lines, linings, and the drums have been turned.  We bled the brakes very good but do you think maybe there is still air in them?  I am running out of ideas.  thanks for all you help.

ANSWER: Can you tell me the source of the power booster that you put on the car? New old stock, rebuilt, from a donor car? If from a donor car what year and model? let me know.
Brad

---------- FOLLOW-UP ----------


Brake booster   QUESTION: Yes it is a aftermarket kit that is new.  Master cylinder and booster came as a bolt on package from Piratejack in Ashville NC.  I thought it was the booster and called them and they sent another one but it is doing exactly the same.
Thanks

Answer
Well this is going to be a full check of the braking system. I have one more question. Were the brake cylinders, shoes, lines and the drums turned when the power brakes were installed or did you drive the car at all before installing the booster and replacing all the brake parts? Let me know.
Brad