Steel brake lines

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.