Headlight Doors:Ghost in the machine
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Headlight Doors:Ghost in the machine
1976 Corvette and I switched the power brakes to the hydro-boost system because of low vacuum on new engine/camshaft and I prefer the performance and assurance of assist with the hydro-boost. Have added a separate electric vacuum pump connected to line going to interior controls, and manifold vacuum from one fitting to pcv and catch can, the other manifold vacuum source goes to the auto transmission and the headlights via a splitter. When I first start the car in the AM after a short while the headlight doors come up but I haven't turned the lights on. If I turn the lights on and then off, the doors stay up. If I push the below-dash switch in, and then out. the doors stay up. After driving around for a while the doors might come back down on their own, or not. Same thing the next day, I use the car as a daily driver. [Never intended to but I like it a lot!] I've ordered a new below-dash switch and the trouble-shooting guide on headlights and vacuum from Eckler. What do you think is going on? Thanks.
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
Up front there you have a vacuum 'relay' up there, maybe even two of them, there are 4 vac hoses going into each relay....3 large at about 1/2" OD, and one small signal hose to the main control valve....
the control valve needs vacuum to tell the relay to suck the lights DOWN, absence of vacuum on the small line will let the relay go to the default position, meaning put the lights UP......for obvious reasons....
so you need a vacuum wiring/routing diagram and go from there, but this maybe enough to get your started....
BTW the center large hose is under full vac from intake manifold....and so changes state in the relay, telling the canisters to life/drop the lights....
most frequent problems are the 'witches hat' seal on the operating canisters, where the output lever goes to the lights, maybe the relay itself......or some dries up hose over some ~35 years or so....
hate it when my hose dries up.....
the control valve needs vacuum to tell the relay to suck the lights DOWN, absence of vacuum on the small line will let the relay go to the default position, meaning put the lights UP......for obvious reasons....
so you need a vacuum wiring/routing diagram and go from there, but this maybe enough to get your started....
BTW the center large hose is under full vac from intake manifold....and so changes state in the relay, telling the canisters to life/drop the lights....
most frequent problems are the 'witches hat' seal on the operating canisters, where the output lever goes to the lights, maybe the relay itself......or some dries up hose over some ~35 years or so....
hate it when my hose dries up.....
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Joined: Feb 2014
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Up front there you have a vacuum 'relay' up there, maybe even two of them, there are 4 vac hoses going into each relay....3 large at about 1/2" OD, and one small signal hose to the main control valve....
the control valve needs vacuum to tell the relay to suck the lights DOWN, absence of vacuum on the small line will let the relay go to the default position, meaning put the lights UP......for obvious reasons....
so you need a vacuum wiring/routing diagram and go from there, but this maybe enough to get your started....
BTW the center large hose is under full vac from intake manifold....and so changes state in the relay, telling the canisters to life/drop the lights....
most frequent problems are the 'witches hat' seal on the operating canisters, where the output lever goes to the lights, maybe the relay itself......or some dries up hose over some ~35 years or so....
hate it when my hose dries up.....
the control valve needs vacuum to tell the relay to suck the lights DOWN, absence of vacuum on the small line will let the relay go to the default position, meaning put the lights UP......for obvious reasons....
so you need a vacuum wiring/routing diagram and go from there, but this maybe enough to get your started....
BTW the center large hose is under full vac from intake manifold....and so changes state in the relay, telling the canisters to life/drop the lights....
most frequent problems are the 'witches hat' seal on the operating canisters, where the output lever goes to the lights, maybe the relay itself......or some dries up hose over some ~35 years or so....
hate it when my hose dries up.....
I'll look into this tonight, appreciate the mental picture of the system up front--I suspect the vacuum lines are the culprit, and/or their connections with operating parts. Will replace the below dash switch when I get it also--seems like that should be working even with the symptoms going on right now but who knows. By the end of this project I'll have replaced every single piece of this car.
Le Mans Master
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From: mount holly NC
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How to test the headlight vacuum system:
http://www.corvette-101.com/vacuum.htm
http://www.corvette-101.com/vacuum.htm
Race Director
Joined: Oct 2008
Posts: 19,191
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From: Long Island
Double check your check valve. Any vacuum leak or low vacuum will cause the headlights to go up.
If the engine vacuum is too low, they make an electric conversion.
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Bllue72--thanks. Would prefer a blue 72 to my white 76. But they're all fun. I'll be spending my weekend in the carport, with the vacuum tester, driving myself crazy.
Race Director
Joined: Oct 2008
Posts: 19,191
Likes: 1,670
From: Long Island
Thanks,
It's a 22660 mile car I've had for 15 years. (72)
I'm rebuilding a 71, green that was painted red. The car is/ was a mess. I spent a lot of time on the systems. It was learn by reading / doing thing. I was a research/design engineer which helped....
I should have done a frame off on the 71 it's that bad. The frame is spotless.. go figure. Everything else was BUBBAED
I helped my friend with his 70, he has a roller cam and nuts-so engine parts. Huge carb... No vacuum. After checking all the lines, switches and valves.. it was apparent the issue was low vacuum. Hooked up a vacuum pump - 1/4 inch hose from my 1980 truck, the system worked fine.
He upgraded to electric, works great. I'm not fond on the look, as I like stock - he loves it
Any year is great, enjoy the car that is what is most important.... make it yours..
It's a 22660 mile car I've had for 15 years. (72)
I'm rebuilding a 71, green that was painted red. The car is/ was a mess. I spent a lot of time on the systems. It was learn by reading / doing thing. I was a research/design engineer which helped....
I should have done a frame off on the 71 it's that bad. The frame is spotless.. go figure. Everything else was BUBBAED
I helped my friend with his 70, he has a roller cam and nuts-so engine parts. Huge carb... No vacuum. After checking all the lines, switches and valves.. it was apparent the issue was low vacuum. Hooked up a vacuum pump - 1/4 inch hose from my 1980 truck, the system worked fine.
He upgraded to electric, works great. I'm not fond on the look, as I like stock - he loves it
Any year is great, enjoy the car that is what is most important.... make it yours..
Last edited by BLUE1972; Apr 18, 2015 at 07:33 PM. Reason: spelling
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Thread Starter
Navigator
Joined: Feb 2014
Posts: 9
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Thanks,
It's a 22660 mile car I've had for 15 years. (72)
I'm rebuilding a 71, green that was painted red. The car is/ was a mess. I spent a lot of time on the systems. It was learn by reading / doing thing. I was a research/design engineer which helped....
I should have done a frame off on the 71 it's that bad. The frame is spotless.. go figure. Everything else was BUBBAED
I helped my friend with his 70, he has a roller cam and nuts-so engine parts. Huge carb... No vacuum. After checking all the lines, switches and valves.. it was apparent the issue was low vacuum. Hooked up a vacuum pump - 1/4 inch hose from my 1980 truck, the system worked fine.
He upgraded to electric, works great. I'm not fond on the look, as I like stock - he loves it
Any year is great, enjoy the car that is what is most important.... make it yours..
It's a 22660 mile car I've had for 15 years. (72)
I'm rebuilding a 71, green that was painted red. The car is/ was a mess. I spent a lot of time on the systems. It was learn by reading / doing thing. I was a research/design engineer which helped....
I should have done a frame off on the 71 it's that bad. The frame is spotless.. go figure. Everything else was BUBBAED
I helped my friend with his 70, he has a roller cam and nuts-so engine parts. Huge carb... No vacuum. After checking all the lines, switches and valves.. it was apparent the issue was low vacuum. Hooked up a vacuum pump - 1/4 inch hose from my 1980 truck, the system worked fine.
He upgraded to electric, works great. I'm not fond on the look, as I like stock - he loves it
Any year is great, enjoy the car that is what is most important.... make it yours..
Really appreciate this forum--lots of help.