I have traced my headlight door problems to the control valves, I think. When I apply vacuum to the diaphram port, the plunger will operate ok. But when I apply vacuum to any of the "operating" ports, they don't hold any vacuum.

There are three ports on teh operating side, one received vacuum from the engine, and the other two supply vacuum to either side of the actuator. One side closes the actuator, the other opens. I can connect my pump to the middle port (engine vacuum) and hold my fingers over the other two ports, and it will not hold any vacuum. I have done this with the "control" plunger (diaphram) in both positions, and with the pump on all varoius ports. They will hold no vacuum. It's like the seal around the plunger part of the valve has lost its seal and it doesn't driect the vacuum to the proper port.

Is it strange for both control valves to have the same problem? This car has been stored in a dry barn for the last 7 years.

If it is the control valves, can they be re-built ?

By the way - The "leaflet" (it's called a book, but it only has 10 pages) Troubleshooting 1968-1982 Corvette Headlight and Wiper Door Vacuum Systems was the best $12.00 I ever invested. Written by Frank C. Prow II. Available at your favorite Corvette supply house. (No I don't receive royalities !!)

Thanks All :troll

 

Here's what I have and the valve is not rebuiltable.

HEAD LAMP RELAY VALVE
DESCRIPTION: Disk shaped steel with an internal diaphragm attached to a black plastic shaft. The upper steel housing has one small metal port connected to a small white vacuum hose. The black shaft has 3 vacuum ports connected to large vacuum hoses. The top port is used to supply vacuum to the actuators to close the headlamps. It is marked with the letter "R" and a red dot; red hose. The center port is the vacuum supply marked with the letter "Y" and a yellow dot; yellow hose. The bottom port is used to open the headlamps and is marked with the letter "G" and a green dot; green hose.
LOCATION: The relay valves are mounted between the headlamps.

FUNCTION: Relay valves control vacuum to the headlamp actuators to open and close the doors.
TROUBLESHOOTING: Disconnect all 4 vacuum hoses. Remove the filter at the base of the relay and inspect it for damage and to make sure it isn't clogged. If it is clogged, the headlamp doors may open slowly.1. Block off the green port and attach the vacuum pump to the yellow port. Vacuum pressure should be maintained. If not, the relay should be replaced. Failure of this test does not mean the relay will not function at all. What it does mean is that once the car is turned off, the holding tank will not hold a vacuum because the yellow port is always open to the vacuum storage tank.2. Apply vacuum to the small metal port and note if the valve moves freely up towards the diaphragm. If is doesn’t, the valve is frozen and the relay needs replaced. 3. Release the vacuum at the small metal port. The valve should sharply snap toward the filter end. Slow movement indicates either a worn spring or the valve is sticking. This will cause the headlamp doors to open slowly. 4. Apply vacuum to the small metal port. Pinch off this hose to maintain vacuum pressure and remove the vacuum pump. Block off the red port and apply vacuum to the yellow port. If vacuum is not maintained, replace the relay.

Hope this helps.
Terry

 

I don't think it would be unusual for both relays to be bad after sitting for any length of time. Here is the rebuild procedure I used. http://iotech.no/corvette/ Click on technical......then "headlight relay repair". The rubber valve (they call it a seal) looses it's fit against the plastic housing over time and will not hold vacuum. The idea with the O-rings is to flare the cup at each end of the valve. I was able to install o-rings without going through that whole procedure by cleaning the cups.....swabbing some 3-M weatherstrip adhesive in them and pressing the o-rings in tightly until it dried. You have to stretch one of the o-rings over the valve for the top cup. I think the o-rings I used were 5/16 X 3/16 X 1/16 thick. I've also heard that if the rubber isn't too hardened you can soak the valves in something called rubber restorer and it helps to make them more pliable.......possibly enough to make them seal again.
Hope this helps

 

Here is a 2nd rebuild procedure......I havn't used this so don't know how well it works. http://www.corvette-101.com/ click "vacuum trouble" Then "headlamp relay valve" then (at the bottom) "headlamp relay repair"

 

I tried repairing my valves. Out of the 2, 1 was a complete failure. The other worked for a day or two then wouldnt seal well in one position. I would try rebuilding them if you have the spare time. New ones are like 60 dollars each. Definately expensive little pieces.

 

I guess I got lucky on mine.....both have been holding for 2 years now. It's a pretty good chore getting them apart and then back together, but since my wife has me on a vette allowance I figured it was worth a try at $60 each. I got to put that money toward some new rocker moldings. :yesnod:

 

Here's an alternative (middle of page) to those relays if you don't mind non-stock.
http://members.surfbest.net/danespac...lact/index.htm

Dane