Master Cylinder pushrod questions

I had the same results as you are getting.

Had a concern on one of my race cars.
It is a 1967 Barracuda that came with drum brakes.
It still had the original pushrod that came in it.

The problem I had was no pressure to the rear brakes, fluid would only dribble out.
They brake pedal was low & mushy.
The front brakes would lock up.

I found out the push rod was too short by accident.
My boy left the starting line & the pedal push rod came out of the MC & rested on the outside of the MC piston & the pedal was setting up high.
I asked him how the brakes feel, He said the brakes were the best he has ever had in that car.

I bought a adjustable push rod & fitted it to the length that worked.
Fixed my brakes by doing this.

Also search the forums by master cylinder push rod length.