The left headlight on my '69 doesn't always go down when the light switch is turned off. The right headlight is very slow to go up. The entire car was recently rebuilt. The door that covers thewindshield wipers is also not going up. After having the problem last night, the left light assembly went down on its own! Help! I've got a spook in the system.

 

Troubleshooting involves many steps, so let's start with a test to narrow it down:

Locate the vacuum splitter/valve that is connected to the intake manifold on one side and then splits into 2 hoses. One hose goes past the brake booster into the vacuum tank. The smaller hose goes through the firewall.

With the engine idling, pull the small hose off and put your thumb over the connection on the splitter/valve.

Let us know if the headlights and wiper door pop up or not.

 

Ok, pulled the hose and put finger over the valve... nothing happen except the enging ran a little rough... now what..

 

I have the same problem on my 68, which wasn't used for years. Someone suggested I spray some silicon lubricant inside the headlight actuators. That helped a lot. One still won't go down by itself, but they open much faster now and the other one closes by itself. I did this about a year ago and it hasn't caused any problems. I don't know if this is a recommended thing to do, but it definitly helped.

 

http://www.corvette-101.com/
Click on vacuum trouble. That's about all the help I can provide as my system seems to work pretty well.

 

Next is to isolate the bad part(s) of the system. You can start with the headlights. Pull the hose going from the vacuum tank to the wiper door and plug the fitting on the tank. If you have leaks in the wiper door circuit they are now plugged so you can concentrate on the lights.

For your headlights you have 2 vacuum relays located in the center front of the nose (68 had only one, you didn't specify year).

By taking the center grill out you have access to the relays. Unscrew them from the car but leave the hoses hooked up.

You will need a vacuum gauge now.

Disconnect the center large hose from the relay (there are 3 in a row, plus a small one at the end of the relay). With engine running measure vacuum. This is the supply hose and should have the same vacuum as the engine.

If it has vacuum, reconnect it. Pull the small hose. Light should go up.

If it doesn't, pull the hose going from the relay to the front of the actuator. Measure vauum. If you have no vacuum, the relay is bad. If you have vacuum the actuator is bad.

That's a start. Once you have this done and working we can move on to the control circuit if necessary.

 

Check the four helper springs on the units and see if they are all there. I would then try lubercating and see what happens.

 

My headlights are acting as an airspeed indicators. They work fine at a stop but at 85 MPH, or 70 with 15 MPH headwind etc., they will pop up and stay up until I stop. I've lubed everything and the springs are all there. Should I replace with stiffer springs??

 

As long as we are troubleshooting the vaccum circuits. My headlights will pop up if I stay on the gas for a long period of time, for instance, getting on the interstate. What would be a cause of this?

 

Vacuum leak. When you're on the throttle there's very little vacuum. The system stores vacuum in a tank which should keep the vacuum relays pulled. You have a leak so after a while enough leaks out to where the vacuum relays can't pull anymore. It takes 2-3" of vacuum to pull the relays. It takes just about none to pop the lights up. So when you are below 2-3" the lights come up.

 

This could be my problem too. The higher speed also means I have my foot in the throttle and less vacuum. However, my lights do seen to pop up more in a headwind.

So, does the tank have a leak or a leak in a line from manifold to tank?

 

This is where you have to do the detective work. The leak can be just about anywhere. Hoses, behind the dash, headlight actuators, vacuum relays... Best advise I can give is to use a handheld vacuum pump and test one piece at a time. For instance, plug the output ports on the tank, then pump up a vacuum in the tank. Watch the gauge for a leak. If that is ok, connect one headlight and test again. If that's ok add the second light, etc etc. Sooner or later you'll find something that leaks.

 

Really strange. My right headlight opens up at night and stays open until I start the engine and create vacuum.

I would think the “at rest� position would be down. What unseen forces are causing the light to open?

I like vacuum issues almost as much as electrical, NOT!

Looks like I’m going to have to learn. Where can I pick up a vacuum pump??

 

The failure mode for the lights is actually the up-position. Makes sense from a safety point of view. Supplying vacuum via the control circuit (headlight switch) makes them go down. Cut the vacuum and they go up.

Your problem sounds like you have a problem with the vacuum relay for that light. It switches to the open position and you have enough vacuum left in the tank to pop the light up. As a test you could try swapping the relays around and see if that makes the other light do it. The relays are about $50 ea and are located in between the headlights.

As for a vacuum pump, I use one of the cheapo mity-vacs available at any autoparts store for $20 or so.

 

I don't want to highjack the thread, but...

I understand, this makes sense, but then why don't the lights go up on their own overnight, or even after months in my garage? I'm guessing it's because there is no vacuum on the relay either, therefore the actuator system is closed and there is no way for the actuators to move?
If I took the hose off the actuator, should the light go up? Just wondering if I have to make an adjustment to the "closed" position, they might be closed "too much".

 

If you cut the vacuum alltogether the lights don't move at all. There's no spring pulling the light up (or down) in case you pull the hoses off the actuator. That's why I think the problem could be the relay. Only way for the light to go up is if the relay commands it up.