vac oper Headlights
Hi Stifler, let me intro myself first since I don't post to this forum very much.
i own a '70 vette and have had it for about 22 years. Do all the work myself including body work and paint. Maybe someday I'll take time to figure out how to put a picture of my car on the forum, but I guess not yet.
I haven't had to fix a headlight vac problem in along time but maybe I can help. If both your headlights do what ever they do in unison then I suspect that you either have a vac leak or poor vac from the engine. look at all your hose connects, put alittle spit on each joint to see if it is drawn into the line. look at your lines for cracks. The thingys that are down under the front valance near the middle of the valance between the headlights are the vacuum relays. These relays have two different sources of vac coming to them. the white hose is from the headlight switch via the manual override switch. I call this the control vac. just like an electrical control circuit which pulls in a relay to control a larger circuit which carries a heavier load. Then along the body of the relay you see three other hoses. the middle hose is from the vac tank. this is just a resouvoir so that you have vac all the time provided the check valve isn't leaking. When the white control vac from the switch pull the relay in one direction the headlights are pulled down an held there. When the vac on the relay is released the relay pulls the other way an the headlights go up. Now at this point i honestly don't remember, but it was suggested that the vac holds the headlights down and I think that is right because if you look at the drawing provided here, the white hose controling the relays is coming from the headlight switch via the overide switch. The overide switch is shutting off the vac when pulled so as to raise the head lights. In any case , if your lights are doing things in unison, then I think everything under the hood at least at the front end near the head lights are ok. The headlight switch and manual overide switch are a real bear to get to, but you may have to check them for leaks. As was said earlier, connect good vac directly to the white hose going down the side of the engine bay to the headlights. if the lights work up and down as you apply and remove vac then that stuff is ok. Another reason your lights maybe doing everything irradically is if the check valve is leaking back. Its purpose is to hold vac stable in the system while the engine will have varing vac based on load and RPM. I believe the check valve is the first little thingy after the vac port connection at the manifold. I think the drawing is labled wrong. Again your system could very well be leaking. The tank can leak too. Just find a way to put vaccum on each component and see if it holds it. Your lights could be mechanically binding at the pivot points of the buckets. You can check to see if the pivots are loose by trying to wiggle them. Disconnect the linkage and move the lights up and down to see if they are tight. And one more thing, if you have changed to a radical camshaft, overlap on the valve timing will reduse your vac to a point that vaccum components just don't work.
