To diagnose the operation of the vacuum amplifier of the brakes, it is necessary to have an engine and several times squeeze the brake pedal. Then shut down the engine and start the engine by pressing the brake pedal. If the pedal vacuum amplifier is slightly applied forward, the amplifier is fine.
If this is not the case, check the reliability of the attachment of the vakumen hose to the intake manifold and to the second connection in the vacuum amplifier housing.
You need to remove the hose to test the reverse flow vacuum valve. Instead, you need to insert a rubber pear and squeeze it in. The air shall pass through the valve, and when released, the pear shall remain compressed.