No. If you decide to use the aftermarket proportioning valve, all you need to do is plumb it into the line TO the rear brakes. If the master cylinder is a dual reservoir and has a separate line that goes only to the rear brakes, yeah I guess you can plumb it at the master cylinder, but I've never done them like that.
Yes it is a dual reservoir, saw two videos of someone just hooking it into the rear brake line in between the master and the stock combination valve. So i think im gonna do it that way.
