I'm about to loss my mind on this brake issue.1977 L82 4 speed Power brakes.
This car has been on jack stans for 2 years, so I installed 4 nelwy rebuilt calipers/ pads
After trying to use a number of bleeding systems.

1. The brake pedal has been stuck on the bottom.
2. THe first Master cylinder was the wrong year so bought the right one from ZIp
3. Bench bleed it.
4. put teflon tape on bleeders so I would not get air back into the system.
5. I got the motive installed using a top board and to C clamps no leaks
6 Bled all four positions inner and outer staring left to right rear, Then left fron to right.
7. removed the motive fron the MC installed the MC top piece.
8. I still have a ver hard pedal that will not come off the floor.
9. Brake light is on.
I have not run the engine, so can it be the distribution block valve stuck in the wrong position?
if so how does one reposition with out causing another brake bleeding issue?
The brake pads obviously are pushed out to the rotors, at least that's what I am inclined to believe.

Any help would be appreciated. I have already gone though 8 bottles of dot 3.

 

So when you bleed it - you have to 'lift' the pedal back up each time I guess? Bummer.

Have you looked at your distribution block? It has a safety sensor that triggers for pressure differential between front/rear and also sets the light and may need to be reset. I don't know that it would specifically cause your pedal to be stuck but it would potentially explain the light. Check threads for testing/resetting the distribution block (it's also often referred to as a proportioning valve but in the C3 I believe it's just a distribution block with the safety valve).

Seems like you've replaced most everything - What about hoses?

 

You are bleeding in the wrong sequence, right side first, right rear inner than outer, left rear same, right front, left front.
Never heard of putting tape on bleed screws.
Pedal should not be on floor with no pressure on pedal.
Is the pedal return spring broken?
Did you damage the master while bleeding?
Is the master piston sitting fully back in the bore?
Did you check clearance between master piston and booster rod using measurement tool?

 

Okay. Have same year motor and tranny and had similar problems. This is what I did and found. Had leaking caliper after I changed one on opposite side. Used my motive to push air through the lines .Placed on top of reservoir the motive and released the bleeder using existing fluid in master cylinder keeping an eye on fluid level in cylinder. I had brake light on also and lightly pumped brake to release light .The teflon on all bleeders could have blocked flow because I would never use teflon. I would and did replace bleeders and opened bleeders gingerly. It will take some time to get that fluid moving but using the pump on your motive with 15 lbs should get u bled rather quickly .
I also used this method on my C4 and worked perfectly. PM me if u have questions

 

Can you lift the brake pedal off the floor by hand?
Just for clarity, when indicating "Left" or "Right" is that you looking from the front or rear of the car?