olelucky

i just reinstalled my engine after a complete rebuild. Previously, all the vacuum system worked correctly. Now, when i first start the engine, the headlights come up for a few seconds then go back down. After that they work correctly with the switch. I did install a higher lift cam. I'm pulling 12-13 on the vacuum gauge. Is the lower vacuum doing this or do i have something connected wrong? thanks
1972 350

Alan 71

Hi ol,
Do the headlight function properly thereafter while the engine is running?
The winking headlights may be a sign of the 'servo' side of the headlight system (large hoses and actuators) receiving full vacuum before the 'control' side of the system (switch and relays).
I'd check ALL the hose connections and if you're using original hoses trim about 3/8" off the ends of the hose to insure a good seal on the various component's nipples.
The amount of vacuum available right at start-up could have an impact on what you're seeing but check the hoses too.
Regards,
Alan

Here's a further explanation from NCRS Member Jack Humphrey.
Each vac controlled item (headlight doors and wiper door) is serviced by TWO separate vac lines: (a) the servo line (vac that actually makes the door open/close) and (b) the control line (vac that tells the servo which way to go--open or closed). If there are leak(s) in the system (generally when there's a leak due to age there's also more than one to track down and kill!), when you're under low native vac conditions (initial engine startup, hard accel), the reservoir tank that's in the system to supply continued vac lacks the capacity to feed vac and the 'circuit bias' (stay open or closed) 'droops' causing the fluxuation of the movable item.

olelucky

thanks Alan, I think I've tracked it down to the headlight relay valves. I replaced both last year along with both actuators to freshen up the vac system. So i didn't think they would be bad this soon. I kept the old ones and hooked them back in. The lights work correct now, just a little slow. I'll order another set. thanks for the help

Alan 71

Hi o,
The actuators and relays available now are notorious for not functioning properly after a short period or even when new.
Glad you got it sorted out!
Regards,
Alan

mikem350

As been said MANY times before, check all new vac components BEFORE you install them.

If you dont have a vacuum pump, a cheap one at HF is in their brake bleeder kit. Decent hand pump with a gauge.

mrvette

DAMN CHINA JUNK has invaded the entire auto parts industry....it's stupid already......BTDT, years ago, thankfully a deer jumped out from front of a minivan and claimed my operating headlights, another headache alleviated.......in the 3 years I had the operating headlights, I worked on them about a dozen times....and each time it was yet another fault, not my doing....relays, seals, even the vac canister, valves, you name it....stupid crap that in fact is not needed......see sites for current looks of the front end......

08Indy

Great Post!

Quick question. Should both headlights go up at the same time?

If so and one is lagging behind the other I would assume that it would be an issue with the parts and hoses associated with the side that is lagging. Is that correct or could it be something else?

SwampeastMike

When everything is tight and working properly they'll pop up quickly and essentially at the same time. A significant lag usually mean there's are significant leak(s) on the slow side. Worn (often the plastic bushings) or misaligned parts can though make one slow by requiring more motive force to operate.

08Indy

They headlight buckets have been completely rebuilt and lubricated.

Interesting though, when I use the over ride switch they practically come up at the same time! Could it be the yellow line from the tank to to relay? By the way, relays and actuators were rebuilt and they are good!

SwampeastMike

That's an odd observation

Check the blue stripe vacuum line that runs between the headlamp and override switches. A kink would cause that sort of operation. If it's not kinked disconnect that line at the override switch. With the headlamp switch on suck through the line--it should be easy--if not the vacuum switch in the headlamp switch is not opening (to atmosphere) fully.

08Indy

With the head light switch “on” if I pull a vacuum on the blue line won’t I just be pulling vacuum against the light switch? This is to check to see if it is sealing properly at the light switch? If it didn’t seal well at the light switch then would I have a problem with both head lights?

Thanks for the help!

SwampeastMike

I mean literally suck on that blue strip line like a straw. With the headlamp switch "on" it should be open to atmosphere so you can suck through it easily.

The entire control portion of the headlamp system is under vacuum with the headlamps turned "off" and the override switch pushed in. Either turning on the headlamp switch or pulling the override switch block vacuum and exposes the rest of the control system to atmosphere. The override switch directly opens the control to atmosphere while the headlamp switch does it indirectly via that blue striped hose. If the hose is severely kinked or the headlamp switch is just barely opening it will take too much time for atmospheric pressure to reach the vacuum relays and one will lag behind the other.

I can't figure out any other problem that would cause the doors to operate in near unison with the override switch but not the headlamp switch.

SwampeastMike

Every C3 Corvette owner should PRINT and study this post!

https://www.corvetteforum.com/forums...tem-works.html

Once you study operation is easy to understand and troubleshoot.

The Achilles heel of the system is the shaft seal on the double-sided headlamp door vacuum motor as it has to form a seal around a moving part subject to corrosion. Fortunately, that seal only comes into play with the headlamp doors open. If you have a vacuum tight system in the "normal" (headlamps off) mode but the doors won't go down properly (or at all) without the motor running or very shortly after turning it off the problem is almost certainly related to that seal be it the seal itself or a rough shaft the prevents even new rubber from forming a good seal. Oiling/greasing the shaft is only a temporary fix.

BLUE1972

When there is no vacuum to the headlight vacuum relay the headlights will pop up. I would check the vacuum check valve.

If you have low vacuum it may take a minute to build up enough to properly operate the system.

Use a mini-vac to test the relay valve for a leak. Any large or medium leak will cause the headlights and wiper door to pop up when the car is started and then return to normal.

I just had the issue on my 72, it was the safety air valve under the wiper arm that failed and caused the wiper door and lights to open and close on start up,

08Indy

OK I finally had a chance to “suck” on the blue hose and with the headlight switch open, you can hear the air going through the switch!
With the switch closed you can still “suck” on the hose however you can’t hear anything .

SwampeastMike

You should be able to hear the air and easily suck through that line with the headlamp switch open because it closes off the other line (it has vacuum) and exposes that one to the open air inside the switch body. You're able to suck on the hose with the switch off yet not hear the air because there's now a path open through to the intake manifold. The switch passed the test...