[randers]

Most logical place to start? On my 78 The drivers side headlights pops up and down perfectly but the passenger side is very slow or delayed (goes up and down after drivers side).It still works but something isn't right. I have printed out the schematics but wonder if someone with a better analytical mind can suggest the best place to start.
Thanks

 

[C3blackvette]

My 80 was having the same problem (passenger side), I narrowed it down to the vacuum relay tree on that side. I took it out and tested it with a minivac to make sure. Going from memory, which is scary, I applied vacuum pressure to the center fitting (mine was yellow) and I blocked the bottom port (Green). It wouldn't hold vacuum so it was shot.
If it does hold, vacuum then I believe you need to put vacuum to the top metal port and the valve inside should move. Yours should be the same vacuum tree, but I am not sure.

I would check to make sure all of the hoses are in good shape first, especially where the hose end slides onto the vacuum fitting. I also checked the actuator and vacuum tank. Of course, the vacuum relay valve was the last thing I checked

 

[toobroketoretire]

Most logical place to start? On my 78 The drivers side headlights pops up and down perfectly but the passenger side is very slow or delayed (goes up and down after drivers side).It still works but something isn't right. I have printed out the schematics but wonder if someone with a better analytical mind can suggest the best place to start.
Thanks

The headlights will raise and lower at different speeds and there's nothing you can do about it. Even when they were brand new they did that so it's nothing to worry about.

The only way they could ever raise and lower at the same speed would be if they were gear driven, tied together, and driven from a common source. But being vacuum operated one will always move faster than the other because of varying friction in the parts.

The later C3's came with two relay valves in an attempt to raise and lower them about the same speed but it didn't accomplish anything major as they still didn't open and close at the same speed.

 

[7t9l82]

The headlights will raise and lower at different speeds and there's nothing you can do about it. Even when they were brand new they did that so it's nothing to worry about.

The only way they could ever raise and lower at the same speed would be if they were gear driven, tied together, and driven from a common source. But being vacuum operated one will always move faster than the other because of varying friction in the parts.
i agree
The later C3's came with two relay valves in an attempt to raise and lower them about the same speed but it didn't accomplish anything major as they still didn't open and close at the same speed.

i agree 100%:thumbsup3:

 

[C3blackvette]

randers,

When you posted that the passenger side is very slow or delayed, how long does it actually take to pop up after the drivers side is up?

 

[randers]

I would say 2 seconds- in the past they popped up and down pretty much together so something has changed!

 

[C3blackvette]

I would say 2 seconds- in the past they popped up and down pretty much together so something has changed!

The passenger side headlight on my 1980 was still coming up as I backed out of the driveway. I would of been very happy if both headlights opened within 2 seconds of each other.

 

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Randers, Toobroke is correct, if its only a couple seconds apart, theres nothing wrong with it. .. 10 seconds, yeah you probably have a leak. Like he said, they never open perfectly synced up. Mine are slow but its because I only have 6 in Hg vacuum .

 

[MIKE80]

Here you go.

http://www.corvette-101.com/vacuum.htm

 

[toobroketoretire]

Most logical place to start? On my 78 The drivers side headlights pops up and down perfectly but the passenger side is very slow or delayed (goes up and down after drivers side).It still works but something isn't right. I have printed out the schematics but wonder if someone with a better analytical mind can suggest the best place to start.
Thanks

Vacuum operated devices that are teed together will never operate at the exact same time. It is perfectly normal for one headlight to completely open before the other begins to open. If however there is a long lag before the second one begins to open that would usually indicate a leaking shaft seal in the second one or a very small pin hole in it's diaphragm.

 

[randers]

thanks much guys,I will let this one go and move on to other projects.

 

[C3blackvette]

Here you go.

http://www.corvette-101.com/vacuum.htm

Thanks for posting the site, its a good reference.

 

[toobroketoretire]

Thanks for posting the site, its a good reference.

Here's something I drew on AutoCad a couple of years ago to help folks understand what happens:

 

[randers]

Thanks-I printed it and will keep in my repair book for the future

 

[MIKE80]

Thanks for posting the site, its a good reference.

No problem.