rear pressure low in system HELP

I know its confusing.....many aftermarket master cylinders don't contain residual valves like the factory ones did...Also, some people say you only need them if the MC reservoir is below the floor which would allow bleed back from the higher calipers....but it won't hurt to have them on anyway.....The master cylinder you are using there appears to be a disc / drum application.....A disc/disc master cylinder has a longer stroke........The reservoir for the discs is larger due to the fact that as the pads wear the caliper extends more and is taken up with brake fluid....Whereas on Drums brakes the added wear is taken up mechanically with the self adjuster, thus a smaller reservoir.... One cheap fix you can try is to place a residual valve in the rear line somewhere and see if that helps ....the 2 lb. ones are for disc and 10 lb. ones are for drums....Also, I like to run the 2 inlet 2 outlet style proportioning valve so everything is regulated through that one prop valve......Just make sure you get a disc/disc valve....