The Camaro vacuum system (Fig 12-15) is like that of a Corvette headlamp system in that they use a vacuum reserve tank with capacity for one and half cycles without the engine running, a vacuum relay valve and an actuator. The actuator is a piston type rather than a diaphragm type. This piston moves to the vacuum side of the actuator as directed by the relay valve. There is no manual valve in the cluster are of the Camaro system.
Instead there is a provision on the relay valve that when moved to one side will vent the relay valve diaphragm to atmosphere. This in turn will cause the relay valve to move and route vacuum to the open side of the actuators; consequently opening the headlamp doors. As with the Corvette vacuum system, the headlamp doors on the Camaro can be manually opened in the event of malfunction as follows:
(Fig. 12-18) Pull outer edge of the door towards the center of the car until the door locks in open position.
Provisions for headlamp alignment are the same as units with the hideaway feature. Door adjustments are accomplished through shims, slotted holes, and floating cage nuts (see Figs 12-13).
It is recommended that the headlamp doors and windshield wiper access door be set in open position during vehicle operation in inclement weather to avoid freezing of the doors in closed position.
source: Chevrolet Service News Volume 39, September-October 1967 - Number 9