Had a incident today that I've never experienced in all my years of messing with cars. A total brake failure! I'm talking to the floor, zero brakes, and the only way to stop the car was to hit the emergency brake and lock up the rear tires!
I was driving around to a few local junk yards looking for parts, when I pulled up to a light. Stopped just fine, but then suddenly the pedal dropped to the floor and the car started to roll. I immediately hit the E brake and it locked up the rear tires.
I pulled into a lot after the light turned, and checked all 4 wheels for a sign of a wheel cylinder leak. All dry, and no signs of leaks. Also opened the master cylinder to check fluid levels, and both reservoirs were full.
I climbed back in and stabbed the pedal to the floor to see if I had even a tiny bit of brakes, and it did stop if I had the engine in neutral and the car was not rolling more than 5 mph. I had about 3-4 miles to get home, so I drove very slowly and used the E brake to stop, with my E flashers on all the way.
I had the wife come out and pump the master cylinder when I got home, so I could watch the reservoirs while she did so. Saw the front reservoir is moving fluid, but the back is motionless. Pretty sure something in the master cylinder failed, but not sure why or what. I ordered a brand new one, and surprisingly they're only $40. Will put it on and bleed them, and hopefully that's the only problem. The rest is new front to back, and the master was rebuilt 10 yrs. ago, but I don't trust it now, so I wont rebuild it again.
I'm sure glad it failed when I was stopped, and not coming up on stopped traffic, as I'd be rebuilding the Canmaro again if it failed at any speed at all! Still scared the heck out of me!

 

ahh.. dang man thats scarry! err. im sure you know this but bench bleed your master before yeah install it makes it a ton easyer. i would eye over your vac lines to break booster just incase. take ur master off makesure u didnt like snap the break booster rod or somethin cause mine was kinda rusty but im sure yours is fine and i doubt that could ever fail. the last idea but it would take some looking is.....

check your soft break lines to the back and your front ones.

those can actually fail w/o leaking they just balloon up and back down w.o a question that could have happened? ur foots on break and it just gave out and balloned up in one of those soft lines and bam no breaks. doent take much of a balloon to make them not work.

 

no brake light? if u had fluid going somewhere the light should come on. otherwise u should be on the right track replacing the master cylinder. so it does not have abs?

 

they dont have ABS they just have a little sensor that controls the one break light if it like goes dry or something it comes on. or something idk how it works

 

No such thing as ABS in 1971. This is old school technology. Yes, I'm sure the vacuum booster is fine, as it doesn't have the hard brake issue that goes with lack of vacuum and good brakes.
I did get the brake light. The same light that lights up when you push on the parking brake, now stays lit all the time. That's what lead me to believe it was the master. You don't have to have it just "going somewhere" to get a light. It will also come on if the brake pedal goes too low, even if the piston is bleeding past.
I'm pretty sure the rebuild I did about 8,000 miles ago just gave up. The long 9-10 yr. storage it had from 1989-99 took it's toll on the brakes, and I guess the honing of the master just wasn't enough to last well.
Ordered the new master from Summit, so once it's on I'll know for sure. As for pre bleeding them, they usually come with the plastic hoses and fittings to purge all the air from the master, so once that's done I'll power bleed the whole system.

 

yeah a master was the first thing replaced on my 79.. 18$ reman from shucks and its great

 

yah u probly got it mastered. lol every time ive had to reset them brake lights its been a pita.

 

A brand new one from Summit was $39, so that's why I went new.

 

yeah. i didnt really care lol. stage 1. get it running. stage 2 get it running better. stage 3 make it look better than duck tape and a safety pin lol

my power valve in my carb blew out so it was running REALLY rich and dumping fuel out the secondary boosters. so i took 2 ziplock baggies and 2 zipties make the bags fit right over the boosters and zip tied them good (secondaries wont open so wasnt scared of backfiring or melting them into the engine) and made it home that way. it wasnt runnable much w.o me doing that because there was standing puddle of fuel on the blades and was flooding out bad.. but it worked!

new power valve and gaskets and a float level adjustment its better than it was before!

 

I had that happen just exactly like that in a Jeep Wagoneer years ago.
I was coming up to a stop sign at a T intersection and stepped on the brakes,it started to slow then suddenly the pedal went to the floor.
No brakes at all,I didn't have time to reach for the e-brake and cars were passing on the highway in front of me at 55 mph...yikes!
All I could do was whip the wheel to the right and drive into the bar ditch at 25 mph.
I had a buddy with me from work and we were going to lunch,should have seen the look on his face lol.
Good thing it was a Jeep and not a Camaro,didn't really do any damage at all.
I put on a new master after doing the same as you did checking it all.
It was good as new but I still got a little butt pucker at every stop sign for a while and to this day I never rush up to a stop sign and count on my brakes to stop me quickly.