Hello everyone, first-time C3 owner here. I just purchased a relatively nice 1977 Corvette with the 4-speed manual and an L82. According to the previous owner, it's "all original except the exhaust".

It has an issue with the pop-up headlights where they open very slowly, with the driver side lagging behind the passenger side considerably. When the lights are turned off, only the driver side light side closes, and only after a minute or two of delay. I looked into it, and this seems to be typical behavior when the system has a vacuum leak.

I went ahead and inspected the hoses under the hood today, and found that the fitting which threads into the intake manifold was loose. Thinking I just spotted the leak, I added some silicone grease to the threads and tightened it back down. But, the headlights still had the same issue. Nothing changed after I tightened the fitting down. I then sprayed some O2 sensor cleaner near each fitting I could find for these hoses, but I heard no change in the idle of the car. I even had my wife looking at the tach for any spikes.

I also noticed that the hoses were not connected the same way as they are in many of the diagrams I've found online. See the attached picture. My index finger is pointing to part "G" in the diagram, and my thumb is pointing to a tee which does not belong there. This tee was added to hose "B" in the diagram, and the small hose protruding from it leads off to the bulkhead on the passenger side. What on earth is going on here? I plan to look behind the dash tomorrow, and I'm hoping someone on here has seen something like this before and can give me an idea of what to expect.

 

You need lube the rod the lights ride on. That may help but the real problem is probably the diaphragm cans.

 

Welcome to the forum. You need a small hand operated vacuum pump with a gauge on it to check each actuator on the headlights to see if they hold a vacuum. You can also measure the vacuum with the engine running at each headlight actuator.

 

Welcome from Idaho, I`m not positive but on your hose B the small vacuum line could be going to the hvac control on the center console,( you could unhook it with the car running and see if it controls the hvac) the only other small vacuum line is on the right side of the engine and it runs to the heater hose shut off valve to the hvac valve-switch in the console. looks like someone changed it. It should work fine that way. On my 77 I replaced the seals on the vacuum servo rods they go bad, but the diaphrams in the servos were fine. I did add a check valve in the vacuum line at the vacuum air tank. seemed to help vacuum supply. One problem I had was keeping the vacuum lines on the vacuum valves by the headlights .they would fall off at times so I put spring band clamps on them, so far so good. When you get the vacuum leeks solved and the pivoits lubricated and the light doors don`t work together and it drives you crazy, you can check out my pictures, there is a equalizer bar I built for that very reason (becuse it drove me crazy) Its very easy to build, got all the parts off amazon and it works great. Still want to try using one vacuum vacuum servo to see how fast it will go but haven`t had a lot of time to play with it lately. I hope some of this helps.

 

Because of differences in the friction, spring, and diaphragm, the headlights will probably never operate simultaneously.

 

• That`s true vacuum also takes the path of lease resistance, rarely do you see the doors open and close at the same time on C-3s. I started playing with them to see if I could get them to operate together, and you can. Built 3 prototypes, first one i used scrap lying around 3/8" rod 27" long angle iron with 3/8" drilled holes for pivot mounts . Though it was to flexy, I changed it to 24" long with heim joints on a 3/16x1 1/2" flat steel, Still to flexy. The third one I used 24" 1/2" rod, not bad, I think 1/8"x 1 1/2" angle iron would be a better mounting plate. with 3/16x1" welded to the 1/2 rod. So using 4 heim joints and 2 clevis`s with steel i`m at about $60.00 for the parts, that`s what I`m using now, It works well. I do have moving pictures but I`m not sure how to post it. They do move together . I think it`s cool. My wife just rolls her eyes, so hard to impress.

 

I think but not sure that you can post a video the same as a picture by going to the "Go Advanced" button in the reply box below.

Pictures of all your mechanical linkage would be cool also. 👍

 

I will look at that, forums is new to me.thanks

 

No problem. We were all new at one time. I know it took me awhile to figure out all of the tricks and it is sometimes different in various forums depending on which software they use.

 

I have pictures at thomas77. It won`t let me post videos.


prototype 1, prototype #2 uses a 1/2 center rod less flex

upper linkage connection points.this link uses a clevis for top link connection. 3/8"

links from rod out to upper linkage

equalizer center 1/2" rod assembly