If you have drum front and drum rear, I would throw the metering valve away. If you have disc front and drums rear, I would throw the metering valve away. If you had disc/drum you would be using a combination valve. The combination valve has a metering valve, proportion valve, residual valve and pressure differential switch, all in one unit.
Disc brakes usually have the pads riding right up against the rotor, when the brakes are off. The rear shoes are out away from the drums, especially if they are adjusted too loose. When you first apply brake pressure, the disc brakes will want to act immediately and nose-dive the car. The metering valve will stop pressure to the front discs until there is at least 40 psi on the rear cylinders. This will overcome the shoe springs and start pushing the shoes against the drums and give you some drag, before the front discs begin to work. No nose-dive.
Did they give you any info with the metering valve? Was it clear which was the inlet and which two were the outlets? There is a rubber boot on one side of the valve. Did they tell you to take the boot off and hold the pin out while you were bleeding the brakes???
