69 Barracuda 318, brake pedal sags

>If you can put a toe under the pedal and manually return the pedal to the top of it's travel, and if the brake-lites then go out,;then the brake-lite adjustment is correct. If you then remove your toe, and the pedal flops down, then it's a pushrod adjustment solution.

Pushrod adjustment
>It's the springs inside the M/C that return the pedal to it's proper parked position,via the pushrod.The clip at the top of the M/C bore, keeps the piston from traveling too far, and coming out. So it's parked position is engineered in. And so you have to synchronize the pedal's parked position, to the M/Cs parked position.

>Assuming the pedal-bushings are free ,If the adjustment is too short, the pedal sags. This will show up, immediately after a new install
> It's also possible that the pushrod started out too long. Then the Compensating port was closed. Then, over time the pedal drops, as the pads or shoes wear, and compensating fluid is never introduced. This will begin to show up weeks after a new install.

>Hang on there is another possibility.
Inside the M/C, after the guts are installed, are three chambers. Two of those are for pumping fluid out to the slaves, and the third chamber is between them. If this chamber is full of air, then it is theoretically possible for the weight of the pedal to push the rearmost piston ahead until it hits the backside of the front one. Of course if it did that, it would take the pushrod with it, and then the pedal would also sag. The result of this, if the frontmost piston is plumbed to the front brakes, would be very poor braking as only the rear brakes would work.
If you suspect this, you will have to figure out how to fill that inter-piston chamber with fluid. This is most easily done by bench-bleeding it with one end slightly elevated, and watching for the air bubbles to finish escaping from that chamber thru the compensating ports.