large travel and soft feel have nothing to do with te booster.
The travel is determined by the MC size and in that respect long travel and soft feel don't go together, a small MC will have a softer pedal (requires less effort) but also a longer throw to displace an X amount of fluid for the same pedal ratio. The other way around for the larger bore MC.
Longer easier toss to the pedal with smaller bore....shorter but harder as you moving more cross section of fluid to manage same volume with larger bore....
what you said above seem the opposite....
Eitehr way, with a vac or hydrobooster,
the pedal and master are still connected mechanically, the only difference is the vac booster has the diaphragm(s) to give assist, the booster has an assist piston, controlled by the spool valve.
right, except for that spring in the vacuum boosters the sharks used....about a inch diameter and inch long between input and output shafts....allows another ~1/2 inch compression within the booster, and maybe 2" at the pedal....only thing my observations can explain ....so the m/cyl goes to full compression , but the pedal still travels....it's a messed up feeling to me....and like I said, most cars feel that way....
but the A to B direct comparo upon install the HB system instantly made the truck m/cyl way too much...so back to stock diameter...
So, without worrying about what kind of assist, the only factor is MC size.
The HB simply gives a very different feel. The "firm" pedal feel with the HB is not necessarily because you have rock hard brakes that are bled properly (something you can get w/ a vac booster too!!) but it's the way the booster operates. for instance, if you have the engine off and pump the pedal until and then start the engine with slight pedal pressure, the pedal first sinks and then you feel it getting pushed back again. This is the chamber being pressurized, the pressure you describe as a rock hard pedal is simply the pressurized system you feel. Only if you do not apply the pedal will the power chamber be bypassed directly to the return line. Depressing the piston will pressurize the chamber.
Depressing the pedal moves the spool valve, closing off the return port first, more pedal will move the spool valve enough to open the pressure port from the pump to pressurize the chamber and this forces the assist piston forward. Release the pedal and the return spring moves the spool back, closes off the pump input and then opens the return venting the pressure in the chamber to the pump.
