danh77

This is on my 77. Both headlights open and close as they should but they don't operate in unison, should they? If it makes any difference the drivers side opens and then the pass side opens a few seconds later. They do make a pretty good clunking noise upon opening. Is there something I should check on or should I just be thrilled they function? Thanks for any and all help

Iceaxe

The short answer is NO, they will not open in unison.

The longer version is the headlights on your car are on two separate and partially isolated vacuum systems. Theoretically they will open in unison if everything is functioning perfectly, but in the real world that seldom happens.

On most well functioning systems the headlights open and close within a second of each other. If one of your lights is lagging behind by several seconds it's usually the relay valve associated with that headlight that is at fault.

REELAV8R

Be thrilled that they function. My 77 does exactly the same thing. I like it. It's a uniquity to the car and it's era.

sullyman56

When I bought my 77 the headlights would open part way and then close. I replaced all the vacuum lines and replaced an actuator and relay. They work now, but like yours, they don't open simultaneously. They do open within one or two seconds of each other and they also make a noticeable clunk as well. I suppose we should be happy that they work.

Alan 71

Hi d,
The system is designed so that the headlights open simultaneously….. and on many, many cars they do. We hear only about the cars on which they don't.
Because there are 2 separate vacuum relays controlling 2 actuators it's possible for them not to.
The easiest way to get an idea of what's going on is to reverse the hoses (large red and green stripes) running from the relays to the actuators.
This allows the opposite side relay to control the right and left actuators.
If the slow opening door switches to the left side you'll know it's a problem with the right side relay.
If the right side door continues to hesitate opening you'll know it's the right side actuator.
So, give it a try?
Regards,
Alan

danh77

Thanks I will give that a try. When I was in college I had a 73 and they didn't work in unison and actually the rt side didn't go but half way up on its own, so I was curious if I had a problem starting that I could fix before it gets worse

mortgageguy

I've always understood that they would not open in unison. The drivers side would always open first because it gets the vacuum first because they are routed in a series. I've even been told that NCRS judges will time the units fully expecting the left side to open first.

mortgageguy

Let me restate that. It's not that they are routed in a series, but the left side has a shorter hose run and reaches full vacuum earlier.

Alan 71

Hi mg,
I really don't think any NCRS Flight Operations Judges are 'timing' the open/close function, and also, I believe the expectation for a system operating normally is for the doors to open and close very close to simultaneously.
Regards,
Alan

Iceaxe

Alan, just curious what you consider Simultaneously? I've spent a lot of time working on my vacuum system and the right headlight still trails the left by about 1/10th of a second. It's about as close to perfect as I've been able to obtain (or seen) but if you are watching it's easy to see one light is trailing the other slightly and I get two distinct clicks instead of one if they were opening in unison.

I'm just asking because I want to know. I've only been around C3's for two years now and still have a lot to learn. Thanks for all your input, I've learned a lot from your posts.

Alan 71

Hi I,
????
If you can hear 2 different clicks (I'd say bangs) I think they can be closer.
I guess I would say if it happens close enough together that you don't even have time to begin to wonder if the second is going to open or close you're doing fine!
Regards,
Alan

I still have all the original components and hoses and they open and close at the same time.
The point that mg raised about the difference in length of the servo supply hoses has no effect once the engine is running, and the vacuum is supplied and a reserve stored in the tank.

Dave J

Alan is right. If the vacuum system is in good condition, the headlights will open just about at the same time. It's when a relay or a actuator has any type of leak the rule goes away.

I have actually connected vacuum gauges to each actuator hose leading to the actuators and timed the vacuum strength, with the result being the same on each side. I believe the difference in 1/10th of a second is probably the difference in the effort it takes to operate the mechanical portion of the headlight door opening. The adjustments must be equal on each side, and normally are not.

Another factor is the time it takes for the vacuum system to leak down after engine shutoff. If it will not hold vacuum for more than a minute or 2, you have vacuum leaks that will affect operation. FWIW, both of my cars hold vacuum well past the NCRS standard which is 15 minutes I believe.

Iceaxe

I'm well inside of this measurement, when I pull the switch both lights pop up instantly, it's just that the RH is about 1/10th of a second behind the LH.


I'll work on cleaning and lubing the mechanical side with the linkage and bushings and see if that helps. I did notice the linkage was a little dirty.

Thanks!

SWO vette

I bought my 77 new and they have never opened together. Ones is slower. My 72 opens together-go figure.