87 stang MC has three ports. If the bottom Port goes directly to the left front caliper and the right caliper comes from the proportioning valve how are both calibers portioned?
That answer is they are not. Only the rear brakes are reduced in pressure. The line going into the combination valve is used by the valve if the front brake pressure is lower than the rear brake pressure. The shuttle valve will then move and put full brake pressure to the rear brakes. This was in case of a leak or issue with the front brake pressure. There are baffles in the MC reservoir that will keep fluid on rear brakes if the fronts develop a leak.
That answer is they are not. Only the rear brakes are reduced in pressure. The line going into the combination valve is used by the valve if the front brake pressure is lower than the rear brake pressure. The shuttle valve will then move and put full brake pressure to the rear brakes. This was in case of a leak or issue with the front brake pressure. There are baffles in the MC reservoir that will keep fluid on rear brakes if the fronts develop a leak.