Odd Vacuum Line Hoses on Newly Purchased 1977 C3
 

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.
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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.

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.

77 vette equelizer linkage
 

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

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prototype 1, prototype #2 uses a 1/2 center rod less flex
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upper linkage connection points.this link uses a clevis for top link connection. 3/8"
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links from rod out to upper linkage
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equalizer center 1/2" rod assembly

77 vette headlight door equalizer link
 

Ok I think I have a moving attachment. The timing on the light doors is slightly off, I have since retimed them

It will accept an MP3 file but I tried an MP4 and it wouldn't take it.

I went advanced and it wont accept any file over 20 MB, so I wacked it back to 14 it was 22 MB. It`s the limits they are using, I guess. you might need to go to full screen to view and hit the side arrow. I like the way light doors work, It was just a simple project I made for myself to do. and no vacuum leaks with all original hoses and valves. Not ready to go to electric motors yet

I don't see any attached file. 😟

Well i guess I don`t have this mastered, I can see what I did was downloaded several pictures from my files (oops) I was just after the headlight doors. You can see them if you click on the red IMG-3674.mov, then the download manager pops up, click on the download complete statement and it take you to a big black screen, (the first screen is blank) click on the right arrow botton and it should take you to the video, Its not very long. There`s other pictures on there that I did not know about (sorry no porn) There`s a NP 246 transfercase picture from a 2000 Silverado 2500 4x4 for sale $600.00 obo, if any one or know someone that is interested app.80k miles orginal from what i can tell. I`m sorry this turned out to be so difficult, but i`m not a computer geek, my kids are i`m not. Still trying

Downloaded the file and got no video, just a steady sound like wind. Don't worry about it. I get the idea. Maybe you should patent it and see if there is any aftermarket interest.

I have put the idea out to several people, it doesn`t seem to be a lot of interest in something like this. Anyone having headlight door problems gp to electric openers and done.. I`m old school I will play with it till it`s dead. Why GM used vacuum doors I have no Idea, but like most products they produce it comes down to cost. If GM can save $30.00 a car x 50k cars it adds up. If I do any patents it would have to be with my new wife. (sore subject here) long story. I could manufacture in small volumes`s, but i don`t think there`s enough demand. Karolysaurusrex, sorry for the side track, how`s vacuum investigation going? That small vacuum line was originally plugged into the vacuum fitting on the back of the intake manifold, I think. It should work ok where it is. I looked on my 77, it`s plugged into the manifold, I changed it to a larger line thru the firewall some time back. Good luck keep us posted.

Downloaded the video on my PC and that worked.

Hello everyone,

It's been a long hiatus - I've had to travel for work and did not have much time to tinker with the corvette. Thomas77 was correct, that small hose lead off to the HVAC controls. I ended up confirming this with a diagram I received with the HVAC hose replacement kit from volvette.com. I'll post a picture of this tomorrow, or early in the week if I can get to it.

I tested the vacuum actuators (diaphragm cans) for the headlights with a hand vac pump and found that they both worked. However, I forgot to test the headlight relays. After replacing all of the vac hoses and doing some troubleshooting with the HVAC vac system, both pop open pretty quickly (not simultaneously, but I'll take it). However, only one of them shuts. I have a feeling it's the that headlight relay.

I ended up tearing into the dash to find a battery drain, and in the process I replaced all of the vacuum hoses and all of the valves which I found to be leaky in the HVAC system. (leak tests were done with a vacuum hand pump) I should mention that none of the HVAC controls were working before this either. Here are the items I replaced (excluding the hoses):
Temperature control valve
AC water shutoff valve
Heater hose water shutoff valve
Blower motor and fan

HVAC controls work now, although that temperature control valve is not the best. If the lever isn't placed perfectly, it'll leak. It feels cheap and plasticy. Also, that AC water shutoff valve (see pic, its atop the heater box) has a really stiff spring. I can't move the temperature control lever all the way to "cold" without that spring forcing the lever right back. The old and leaky AC shutoff valve I replaced also did this, and I expected the new one to be less stiff or more lubricated. But no amount of tension/length adjustment in the control cable could overcome that spring without me holding the lever all the way to "cold". On top of all that, the air being blown by the fan is very weak, even at full blast. I can barely feel the air with my hand up against the vents, although it is there. So, more puzzles to solve.

I also had the chance to calculate my fuel mileage, since I fulled the tank up for the first time while counting miles on the ODO. I got 7mpg! Something is seriously off, maybe with the carburetor or fuel pumps. Cold starting is very difficult and takes multiple pumps of the gas pedal, so I'm guessing it might be an issue with the fuel system.
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You're making progress. For the fuel system problem and hard starting, check the choke valve when the engine is cold to make sure when you floor it and release it that it is fully closing and the accelerator pump is squirting a shot of gas in at the same time.

Welcome to the engineering marvel of the C-3`s. No the HVAC control is not impressive, I replaced my 77 controller a few years back The old one completely fell apart and the temp lever broke in half. The new one is flexy, 77 was the first year for that controller. It takes time to find the sweet spot on the controls.you might try hooking up your vacuum pump to that valve, I think that spring is strong to compensate for the vacuum. play with it. The air volume is not great even on its best day, make sure the max vent servo and door is working right. I hope you have the right fan and motor, It will make a difference if the engine is running, more voltage faster fan. If you want to see how much crap is inside your hvac case in the bottom. you can pull the fan speed resistors from the top of the case, (two screws) and see the bottom. debree coats the front of the evaporator. and slows down air flow, might be a good time to vacuum and blow out the vents. (if you haven`t already) 7 mpg thats impressive, Are you smelling gas when you park? ( I had to replace my fuel pump return line, it cracked and had a strong smell in the gerage leaked all over the top of the fuel tank) Hopefully your fuel is not more than 10 percent ethenol. check your engine oil to be sure that you don`t have a fuel pump leaking into the engine oil. Cheap made gas burns faster for some reason . Good luck. Keep us posted

I read an article years ago that said you could use a C4 fan to move a greater volume of air. It did require a spacer between the fan and the ductwork.

Mr. 73 shark I saw the article about C-3 fan performance you were referring to I believe, It was an article on Digatal Corvette forums on 1/3/2014. Interesting article.
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Good find. I'll have to look it up again and print it out. Since I currently have the engine out, it would be a good time to do this.

Found a fan and motor on rockauto, a/c delco for $38. I can`t find a ready made 1" spacer, but amazon had 1"x12"x12" plastic for about $25. I will make a spacer. I think it`s worth a try, thanks for peeking my interest..

You may have to post a link to that particular thread on Digital Corvettes as they changed their password requirements since the last time I was on there which was a lot of years ago. I asked for a new password.

I seem to remember from when I read the article that they used a piece of 3/4" plywood for the spacer. If I'm looking at this right, the extra portion of the C4 fan will actually be inside the spacer which will limit its effectiveness to increase air flow.

Let us know how it works out for you when you get it done.

There was no password, it was an old story I ran across. I will go back and see how i found it. when i saw the story i remembered what you said about the C-5 fan and motor. this guy was using two pieces of 1/2" plywood glued together to make 1" spacer. then he mixed up some fiberglass resion to coat the wood for water proofing. I will search for the post.

I found it by google search Poor C-3 Air flow-Blower Motor. And it took me to Digital Corvette story. No log in No password, I did get the date wrong it was jun 3 2014 not jan (reading has always been hard)
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C-3 hvac modifications

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Thanks, found it.

I see that he used a C5 blower. Is that what you got?

tThe fan and motor in that picture is a NAPA motor and fan and their proudctsare always good, But I went with A/C Delco I saw in another picture, I find it easier to order from rockauto sometimes. This a/c delco is for a 96 corvette, were the off set motor and fan makes the fan 1" longer. so thats why the spacer, and its a larger amperage motor (so they say, haven`t seen the spec. difference) So longer fan and motor. I will try anything once, I found more pictures, the spacers
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look to be plastic, they look like mock-ups and not for sale.(how easy would that be to just buy a spacer?)

Also found a reference chart on amazon (should be right) They made this fan and motor for a lot of vehicles.

https://cimg3.ibsrv.net/gimg/www.cor...c48c02aea1.jpg

From what I can find 1984 C-4 cars used two fan types, some like C-3`s and a longer one. C-5 used all long types, looks like. Spec`s on the blower motors and fans are not very good. So beware . Found numbers that should be good, two are from these pictures above. NAPA BK #655-1778 used from 86 to 96 corvetts, A/C Delco #88959521 and GM # 12491240. So 86 to 96 corvette fans should work. DIY on the spacers as far as I can find.

Let us know how it works out and if you notice increased air flow. I'm still worried that the extra portion of the fan being partially hidden by the spacer and whether or not that will restrict its contribution to increased air flow or not.

Ok I will check it out, got the fan and motor today. It will be a few days for the 1" plastic. I will let you know, once I get it together.

Don't waste your time fixing what was junk, when the car was new. install electric headlight motors, and be done with it.