80 vette, ls1 setup.

Everything is new except the hoses but they all appear good condition. I tested the older parts using the how to test them article and they do work.

Engine has not ran for two months. Started it, tried the lights and the driver side popped open quick while the passenger side struggled. However, once the engine was warm the lights would not even try to open. So far, thats the closest I have had them work since I started to modify the car years ago. One thing I noticed is I have great vacuum by the one way valve/filter but by the time it goes under the dash it is very little. So I decided to bypass the light switch and override... hooked it up direct from the one way valve and still nothing.

I am stumped and getting very very very

What would you suggest?

 

Since you have already modified it keep this in mind. I'm changing my whole headlight system on the 76 so the electric one on it will be for sale later on this year.

 

how much? first dibs

 

It's a lot easier to learn about the vacuum system and then fix the lights, rather than re-engineer the car.

 

Learning how the vacuum system works instead of guessing about it.

Check the inline filter (white plastic). If memory serves, it is a one way valve.

 

Thats new. Installed correctly. I have the whole diagram memorized now.

I just don't understand how/why the headlights would not work then the car sits for two months and one headlight pops up perfect while the other stutters. Then they stop working after the engine is warmed up. Even bypassing the switch it still did not work. However, hook up vacuum gauge and they work.

Even though hoses are new going to replace the main ones towards the engine... maybe one got melted, pinched or something that I don't see.

 

Hi g,
Trying to figure out just what you have.
You say "everything except the hoses is new"; but then you say you "tested the older parts".
Just what parts did you replace? And did you test the new parts before you installed them?
It's very rarely the hoses. It's often a problem with the headlight switch, the headlight relay, the headlight actuators; or the way the hoses are hooked up. It's very easy to get the hoses mixed under the dash or at the relay.
What trouble shooting guide are you using; and does your vacuum pump have a gauge on it?
Regards,
Alan

 

My 71 would not lower headlights once engine was turned off, but would work ok while running,,,,indication a vacuum leak.

With just a couple pieces of rubber hose, a vacuum guage and a mtyvac vacuum pump I was able to troubleshoot and find the problem. If you have a schematic and a bit of common sense, just connect one of the hoses to the vacuum source on the intake manifold and just hook the other end to different places while measuring vacuum with the guage,,,,you will be surprised just how easy it is to locate the failing or leaking system.

Hooking the test hose to the engine works better than a vacuum pump as the vacuum pump requires a whole lot of pumping to build up or should I say reduce air pressure,,,,such as excavating the tank,,,takes just a couple of seconds to do so with the engine running.

Corvette as usual does not make it easy to squeeze your hands down to the tank fixtures to swap hose around but if hands are small it can be done.

Turns out on my car, that when I isolated the windshield wiper door assembly from the rest of the system, all then was ok. I have a leak somewhere in that system that I will deal with later. I already know that the main actuator assembly for the door is leaking,,,the problem is that a replacement is about 140 bucks,,,,no rebuilt kits available that I've found yet. The little if ever driven in the rain, I think that I will let it go for now.

Now if I can just get my speedo out to clean the inside of its fogged up lense,,,the gasket has apparently failed and lets contaminants in. A somewhat rotten job,,,,now that I'm into it, seems not worth the effort but I'm already buried. Probably a good time to change light bulbs and lube tach and speedo cables too.

 

New check valve, new filter, new actuators relays. Tested the actuators and they were perfect. The headlight switch is original, the coffee can canister is ~5 years old and the override switch is new.

One thing I noticed is I have more vacuum at the check valve but lose it by the time it comes into the car. Thats why I am thinking pinched or broke line.

The articles I used are

http://forums.corvetteforum.com/c3-tech-performance/2736499-how-your-headlight-vacuum-system-works.html
http://www.corvette-101.com/vacuum.htm

 

Did you troubleshoot the headlight switch? It is the least fun part to replace.

 

Just because a part is new doesn't mean it's working correctly. I would suspect the passenger side relay. While you "tested the actuators and they were perfect", you didn't say you tested the relay.

Since the driver side headlight operated properly, your passenger side problem at start-up is somewhere in the part of the system that is unique to passenger side headlight.

That means all parts that are common to both headlights are likely just fine, including filter, check valve, light switch, bypass switch, vacuum reservoir, and related connecting hoses.

So concentrate on parts and hose connections for the passenger side headlight. A couple years ago I started this thread, which is now a sticky, that might help:


The Willcox website also has nice vacuum system schematics and how-to testing tutorials.

Good Luck!

 

Willcox Headlamp Vacuum System Diagnostic Video 1968-1982




It's only a few weeks old.. but it shows you how to test each item in the system.