I haven't posted much here as I've been having more fun driving after I completed SNKVNNM some 6 years ago, but a couple of years ago, I replaced my manual brake system with a Whitby power brake system and while I've had no major problems, I thought I was having an issue with the master cylinder since day one. A year ago, they thought like I did, that the MC could be bad and they sent me a new one.

I FINALLY got that installed but it's behaving the same way; the main issue: if you press hard on the brakes, fluid in the front reservoir bleeds into the rear reservoir via what I suspect is a check valve to equalize the pressure in both sections of the bore in the MC, but the rear reservoir keeps filling up until it starts to bleed out of the vent hole while the front get's low.

So my big question is: do I need a proportioning valve such as the one that normally comes from the donor? I got rid of that when I had manual brakes but after thinking about the transition to power brakes, it came to mind that perhaps I need the proportioning valve. Would that solve my problem?

TIA