Classic/Antique Car Repair: 1968 camaro 4 wheel drum brakes, 68 camaro, 1968 camaro

Question
QUESTION:  I have a 68 camaro with 4 wheel manual drum brakes. the system is all new except the proportioning valve, I've bled the brakes about 6 time looked for leaks and adjust the brakes and my brake pedal still goes down almost to the floor. The car will skid to a stop if I hit the brake hard but the brake pedal travel as me worried.

ANSWER: Several questions:
1. Is it power brake system?
2. Is the pedal firm when it is pushed down or is it spongy?
3. When you adjust the brakes do you tighten the adjuster until the wheel just barely turns and then back off about out 14 clicks?
4. Have you measured the drums to be sure that one or more is not worn oversize?
Brad

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

QUESTION: No they're not power they'manual, the pedal is firm but only at the bottom I have notthing until about 3/4s of the way down. and like I said bfore everything is new, and adjusted

ANSWER: I have one more question for you. When you first put the car together were the brakes good and then the pedal get lower as you drove it?
Brad

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

QUESTION: No I have never been able to get a good brake pedal

Answer
If I had the car in my shop with this history, I would have all four wheels and drums off. I would check each wheel for proper assembly paying close attention to the operating pins coming out of the wheel cylinders, self adjusters to make sure that they were on the proper side of the car. The adjusting levers should be marked R and L. Check to see that the adjuster screws are installed correct. They should  lengthen when the adjuster lever turns the screw. They can be installed on the wrong side. Check the drums with a drum micrometer to make sure that they are not oversized by more than .090". If everything is right we are back to the master cylinder.  Make sure that the pedal comes all the way back after each stroke. Check the free play, that is how far down the pedal goes before you begin to feel resistance. It could be the wrong master cylinder or push rod. If all checks then replace the master cylinder. Good luck.
Brad