Deuce brakes

[Jake0147]

We also don't call air brakes "air over mechanical spring brakes"

I agree that it really doesn't matter what they are called as long as they work.

Only the parking brake would be "air over mechanical spring"... Quite right, but since all conventional brake systems end in mechanical braking, that part is dropped from the nomenclature and assumed to be there unless otherwise stated or implied such as hydraulic retarders, regenerative braking, etc. Then they'd have to be mechanical over before anything as well, as you always have to push a pedal, lever, or maybe even a switch, then it'd be electric over mechanical over whatever... That part is assumed as well.

I really don't care what they're called either. M35Tom is very correct, the hydraulic link can be technically broken while the brakes are in operation. Yet the connection is there in one form. Take away the air in mid stop, and the brakes continue to work based on the fluid alone. So even in an interrupted state, the hydraulic system remains a primary system, and the air remains secondary.