I have a 1972 coupe and if I get on the gas to pass someone on the highway the drivers headlight goes up. When I let off the gas it goes back down. Also, when I turn on the headlights the drivers light goes up quickly, but the passenger side takes several long seconds. Anyone know what might cause this?

 

You have the infamous vacuum leak somewhere in the headlight system​​​​. Could be a hose is cracked or a vacuum relay. Use Google and search for some posts that give step by step instructions on troubleshooting. Welcome to the ancient world of vacuum controls. 😬😬😬😬

 

The fact that one headlight goes up before the other is nothing to worry about. Almost all of them do this.
The headlight raising on hard acceleration is a loss of vacuum in the small switching line. The small line that goes through the over ride and headlight switches then goes to the top of the switching relays under the header bar.
when they have vacuum the relays switch to the close the headlight doors. When they have no vacuum they switch by spring pressure to the open the headlight doors position. The large line is supplied by engine vacuum just the same but has the vacuum storage tank for back up. And the small line is connected differently and doesn't get much help from the vacuum storage tank.
The first place to look for your issue is the vacuum check valve. Generally very near the base of the distributor, just drivers side. If the check valve doesn't hold. Your headlights pop up under acceleration. As engine vacuum drops to near zero under wide open throttle conditions.

 

Thanks for the responses. I changed the check valve years ago, but I will start there again. My mechanic wasn't too keen on tracking down any vacuum issues.

 

I second the check valve.

 

Hello,
Dr. Rebuild has a trouble shooting guide for the headlight system that allows you check the operation of each component individually.
It doesn't make it easy but it does help you to determine where the problem (s) likely is.
I believe the guide is just $4.
Regards.....

 

Thanks Alan I will follow up with that.

 

I picked up a smoke machine for $100. It comes with all sorts of adapters. Runs off of Baby oil. I was trying to chase a vacuum leak on my engine.

 

Go electric, I did this recently and significantly happier with mine.

 

Nahhh, something really satisfying about repairing the stock system.

 

A sub par (if there is one)electric headlight system is still better then a 100% working pneumatic system.

 

My factory system worked perfectly for 45 years. That's actually pretty reliable when you think about it. No car is actually designed to last that long.
I have rebuilt and repaired the system. It holds vacuum like Fort Knox. So, maybe it won't last another 45 years. Maybe it will. But electric motors and there switches can also fail.
Nothing perfect. The vacuum system is actually very simple once you understand it. And very reliable.

 

I made my own smoke machine for less than $10 Works great. Burns baby oil so it makes your engine and garage smell fresh.

 

I use a cheap harbor freight vacuum pump and use an extra long air hose as a vacuum line. I place the pump in another room and use a remote light switch ot activate the pump. With a gauge at the intake line I can see when I get to 15 inches then shut it off. Its a lot easier hearing a leak of finding a leak without the engine running. The system holds 2 different vacuum systems. One to tell the headlights and wiper doors to open and the other to do it. Since yours is opening and then closing it is most likely the hose that goes to the top of the top of the actuator relay. THat hose pulls up on the valve that is internal to the relay and when you lose vacuum it lowers that valve openning the headlights. That hose comes from the headlight switch. Since you are losing vacuum on acceleration and deceleration then you most likely have a leak in the supply line after the one way valve or the lines that attach to it, the tee that goes to the wiper door, the headlight switch on both sides and at the relay valve. if you cut off a 1/2 inch to inch of each end that is plugged into those items then you will most likely solve the issue of the accel and decell.

slow headlights are a leak on the other side that controls up and down forces. Again you have a leak most likely from the actuator relay to the relay them selves. on the slow headlight. IF its slow going up and fast gong down then is just the upside hose, if its both then its the vacuum line that is the supply side of the realy

 

https://www.corvette-101.com/vacuum.htm



Can't you check each part to find the problem?