ok, trying to figure out the headlights on this '71... what makes 'em pop up?... when I shoot air down the vacuum lines after manually raising them, they drop down fine, but for the life of me, I dont understand how theyre suppose to work? (can ya tell this is my first vette?)

thanks in advance,
Timbo2 :confused: :confused:

 

I can also tell you are a newbie.. you'll have better luck in C3 section.

basically engine vaccum runs the headlight doors and the wiper door on all 68-72 cars. is there any reason why you are opening them manually?

 

There are two vacuum lines that operate the headlights. A large line and a small line. The large line goes to the vacuum reservoir and provides vacuum to the actuators through the control valves. The small line is the control line and runs from the headlight switch to the control valve. If the control line has no vacuum then the valve moves to the open mode and routes vacuum from the reservoir to the side of the actuator that opens the headlights (that way if you get a hole in the control line then the headlights default to the up position). If the control line has vacuum then the valve will move to the closed mode and routes vacuum from the reservoir to the side of the actuator that closes the headlights.

It's a vacuum system so to properly troubleshoot the system you need to suck air out of the lines not add it.

To troubleshoot the actuator remove the actuator vacuum lines from the control valve (make sure you remember which one goes where) and suck the air out of the lines one at a time with a vacuum pump (you can get one from autozone etc. for @$30). One line should raise the headlight the other should lower it. If it doesnt then its a bad actuator or a hole in the line to the actuator, swap hoses to make sure it's not the hose.

To troubleshoot the valve, manually lower the headlight then disconnect the control line from the valve. Then disconect the vacuum line from the reservior. Then suck the air out of the line that you disconnected from the reservior. The light should go up since there is no vacume in the control line.
If the actuator was good and the light still won't go up it's a bad valve or a hole in the line to the valve, swap hoses to make sure it's not the hose.. Check both valves.

If both of those tests were good then re-attach the vacuum lines to the reservior and suck air out of the other side of the reservior. If they don't go up then you have a leak in the reservior. connect right to the reservior to take the long hose out of the equation.

If all of those tests were good chances are you have a leak in the large line going to the reservior.

Hope this helped,
David



[Modified by GATOR454, 1:00 PM 12/12/2003]

 

It's a moderately complex system. There's a diagram of it at http://www.corvettefaq.com under the "Misc" section. You're probably having trouble with the actuator relay valves since you can suck 'em down but you can't suck 'em up. These have seals inside which give out over time. You can rebuild them (search the archives--someone posted instructions a couple years ago), but it's a lot easier to buy new ones. Kind of pricey (about $70 a pop last time I checked), but you can run your headlights off of one of them if you use connectors to run all the hoses to it.

JB