All brake tubes on all these cars are 3/16 but there's a catch...........fittings such as t he original drum warning switch or the later combo prop valve, and the master, have special fittings, which were designed so things could not be hooked up incorrectly
I guess anything could happen.........rust, etc in the system, stuck valve, and there's talk of expanding (plugged) brake hoses
Just exactly what does it do?
No pedal
soft pedal
leaking down pedal
poor stopping performance
Can you determine if front or rear is not working well.........try a skid on dirt, etc?
A booster adds a second layer
Booster could be bad
You might have low vacuum to the booster
Last, when "mis" matching parts, you can create a situation where you just won't get good performance. Smaller rear wheel cylinders teamed with a too large master, for example.