new member to the site, need some help with my brakes.

I have a 1976 Monte, I was driving to the gas station the other morning when i thought i heard a pop then my brake pedal went all the way to the floor still alowing me to stop just not very quickly. First thing i did was replace my master cylinder and still the pedal got floor. The next thing i did was replace my power brake booster and still no dice. I have bled the brake lines multiple times with no success. When i take the bleeders of im getting fluid but when i put them back on the problem still remains. Before I replace all my brake lines i wanted some feedback from you guys maybe i missed something??

 

When you replaced your Mast Mast were Cylinder did it come with a Proportioning valve? Does it have individual hoses to each brake or is there a splitter for the rears?
Could you tell where the pop sound came from? Anddoes your brake booster rely on a Vacuum line? Have you done any mods to the brakes that may be at fault? Do you have Disc all around, or do you have rear drums? What is the condition of you brake calibers?
These are the questions I would ask myself.

 

The master cylinder did not come with a proportioning valve but there is one on the line, there is a splitter for the rears, pretty sure the pop came from the booster after i took it off there was alot of rattle inside it, it is vaccum line, no brake mods they are all drums, and the calipers are in good condition not new however. Im going to try the proportioning valve next it slipped my mind until you reminded me. I'll let you know the results.

 

Could also be a simple vacuum leak too. Check to see if the brake booster line is in good condition and is still connected to the manifold, I have had mine blow off before.

 

Here is what I think happened.... Generally a brake booster will let go when a master cylinder starts to leak thus causeing the fluid to eat away at the boosters rubber seal.
Since you said you replaced the booster..did you replace it with a new one? or a used one? Brakes are just as important as the driveline... I would never consider "Used" parts when it comes to brakes... If you did get a "used booster" I could also be faulty.... Recommend getting/purchaseing a new one.

The 2nd question I have...Did you bench bleed the master cylinder...Before... You installed it back in the car? If you didn't...Theres the reason you still do not have a solid pedal.

 

Like Dave suggests, tha master cylinder too can have air trapped in it, in turn causing a no pedal situation. You need to have a helper pump the brakes about 4 times and then hold the pedal down while you crack open one of the steel line connectors on the master cylinder. repeat 2 or 3 times. Insure your fluid level is always topped of. Then repeat on the 2nd steel line ln the Mstr Cyl. Now go and bleed your brakes all over, insuring you keep the fluid topped off at all times.

Just did a used $15 master cylinder from pic-n-pull on my GMC about 30 min ago.

Did it all by myself using an adjustable trekking pole, drain pan and the bottle method. Took all of 15 minutes.

 

Brake booster and master cylinder are both new. I bled the master cylinder with a helper (pumping the brakes) also vacuum line is good. I have not messed with the proportion valve yet. I'm leaning towards that being my issue I should know by tomorrow afternoon and I'll be sure to let you guys know how it goes.

 

By pumping the brake pedal with the lines attached doesn't bleed the master cylinder as its drawing air back into it from the air in the lines...

A proper master cylinder bleed consists of running plastic flexible lines (that came in the master cylinder kit) and filling the reservoir with fluid and putting the flex tubing into the resevoirs and recycleing the fluid back and forth just thru the tubeing(one on each chamber)....that way you will visibly be able to see all of the air removed from the master cylinder... before you can even begin to think about bleeding off the rest of the system.

If you did not bleed the air out of the master cylinder properly....
Your just chaseing your tail...