My 73 has the popular headlight problem. When I turn on my lights they will not come up. If I lift them manually they are fine. When I turn my lights off they go down, first the left and then the right. What is the solution. Thanks

 

Very common on 30 year old cars. First, I would replace all the vacuum hoses in the headlight system (usually comes in a complete kits for your exact model year) including a new filter and check valve. Vacuum pulls them up, and you may have just enough to hold them up after manually opening them. The springs pull them down once the vacuum is released.

You may also need seals for the cannisters. They are sold separately, and much cheaper than a new cannister.

Didn't you want yet another weekend project on your favorite car?

Spike

 

don't think there are seals in the 73 canister. Your canister is actually a huge structural tube between the front frame horns.

DO they come up if you pull the switch, then rev the motor and snap the throttle shut?

Did they ever work before?

 

Actually, it takes vacuum to pull them down. There is a toggle link that "breaks over" at full open (kinda like locking your knees). The actuator is still needed to pull (or push) the "knee" to a bent position. The spring's probably just a counterweight (like on a grage door). You can lift them from outside by just pulling on the cover, but you need to reach up inside to move the toggle in order to lower them.

I'm guessing you have faulty vacuum relay(s).

 

It does have canisters. It also has a tube between the frame rails. I tested it this way ... I can pull off a hose from either canister, blow into the hose and the light comes up. Then suck on the hose and it goes down. It seems that it should produce forced air to open them and vacuum to close them. They will close but will not open under normal operation. Is there a particular part that converts the air from vacuum to forced air and vise versa?? Thanks

 

NO .... its been a while since i fixed mine but they work by vacuum on both sides of the diaphram in the cannister which is controlled by the relay mentioned before what you did by sucking and blowing on one hose makes the sytem work kind of opposite to how it was designed. when you blew on the hose (or pushed it with air)... what there should have been was vacum on the other side of the diaphram to pull it.

 

OH, I just realized, it could also be the signal line from the switch! It's vacuum, too. Runs from the vacuum canister to into the switch and then back out to the relays. Depending on the position of the switch, it sends vacuum to (or atmospheric vent) to the relay diaphragm(s) causing the piston to slide from one port to the other. Your signal hose and/or switch could be leaking.

 

Important stuff to check... headlamp switch, under dash "pull down" switch, make sure you have a vacuum filter and check valve installed. What you described as "canisters" are actually your vacuum accuators

If you need more help.

click here and hit "vacuum trouble" on the left

Hope this helps, I've got a 73 with working vacuum if you need pictures let me know.

--Mike

 

Could you get both of the headlights to operate off of one relay?

Sorry to thread hi-jack

 

I got my first vette back in August and one of the first things I did was the lights and the vacuum lines. First all the headlight actions work on vacuum to one of the two ports on the large vacuum canisters. The vacuum to each canister is controlled by a vacuum relay switch that is itself vacuum operated. On mine these were what had gone bad.

The way I found out way to connect a piece of vacuum hose to each port on the canister and suck! If the lights move or you feel resistance then your canisters are likely not the problem.

However you are likely to find as I did that it is the vacuum relay switches and not the actuator canisters that are the problem. The fact that you get any movement in your lights would indicate that the actuator canisters are functioning at least to some degree. A vacuum leak in the line is still a possibility and I would certainly eliminate that possibility first.

If the relay switches which are mounted to the underside of the middle of nose inboard from the actautor canisters are your problem do a search in this forum. There are a number of helpful posts including an excellent one on how to repair the relay switches. I did it and it was a lot easier than I thought it would be! And it cost me $5 versus the $50 or more to get new or rebuilt ones and my lights work great now.

Good luck.

 

Hope this helps, I've got a 73 with working vacuum if you need pictures let me know.

--Mike[/QUOTE]


Mike good job on that vacuum trouble shooting guide that will help out a lot of people. thks for the effort

 

Great Post!.....

 

Thanks, but could you help a newb and give the title of the thread with the repair instructions? There's a lot of headlight threads, and most of em I've read say to just replace the relay.

 

Sure. The early cars only had one for the lights. Not sure why they changed...

 

This is post I found the most useful. It was how I repaired my relays. I had to take one apart twice. One of these relays will run you ~$60 from Ecklers. While you might find it cheaper, I doubt you'll beat the $5 or so I spent at the local auto parts store on a variety pack of O rings. Plus if you know your relay is bad what have you got to lose?

http://forums.corvetteforum.com/show...t=vacuum+relay

 

Jumping on the end here but I had the same exact symptoms in my '78. It was simply the headlight switch that needed to be replaced. I really shouldn't say simple 'cause it wasn't easy getting to it. Here's apretty good link with vacuum system info.http://www.vettevacuum.com/index.html

 

Excellent post guys. I have been thinking of rebuilding my headlight relays for a while now. I think I will give it a try and see what happens. They are after all 35 years old. I don't think I can do any damage to them.

 

 

Here's a link....once there click "relay repair".
http://iotech.no/corvette/.
Use this mainly for disassembly. You need (2) 5/16" X 3/16" by 1/16" thick O-rings and some weatherstrip adhesive or RTV to hold them into the cups at each end of the rubber piston. No need to grind the axle ends or add washers. Push one in the bottom cup and keep some pressure on it until it sets up.....then strech the other o-ring over the piston and do the top cup the same way. The whole idea is to flare the cups so they make good contact with the cylinder.