If master is too small, you won't be able to get solid pedal or none, even tho all is bled good. Even smaller amounts like 1/8" make a big diff. I didn't believe it, and tried it, never did have good brakes, till I got correct size Master. 80 series is a Big rig, close to 1-1/2" bore I bet, and 20 series only has about 1". Am I correct? The clutch sides are usually 15/16", and may stay the same on those.
It's about "Volume" needed to run all the brakes, not just Pressure.
