I'm not sure if my tucks are plumed the same way yours is, but the master cylinder does not provide any pressure to the brakes (well, if the 'vac in inoperative it does provide a little pressure via the control lines... but not enough to stop rapidly).
The 'vac provides all the pressure. Any modification of (well, my truck, at least) would not involve any changes to the master cyl, just a proportioning valve at the end of the vac hydraulic cylinder.
This is for a Series I, II or III vac.
Any system involving a remote vacuum assist the master cylinder is just a control valve and a fluid reservoir. The vac does all the heavy lifting (typically 1000-1500 psi for a series III vac).
Last edited by pfarber; 03/06/2014 5:54 PM.
