Headlight Actuator Relay Valve?
Thread Starter
Racer
Joined: Aug 2013
Posts: 480
Likes: 95
From: Georgetown Kentucky
Headlight Actuator Relay Valve?
I've gone through checking the vacuum to see why my headlights aren't opening and closing and the problem appears to be both Actuator Relay Valves. 12" to 13" of vacuum at 800 rpm at the manifold side (same reading I get at the manifold). About 2" on the other two ports of relay that go to either the front or back side of the vacuum diaphragms that move the linkage for the headlights. Both actuators seem to just be leaking vacuum significantly.
My question is can these be reconditioned or do they need to be replaced?
I don't know what the inside of the relays look like but if there are seals in there .... I guess they've dried up.
The headlights do go up and down when vacuum is manually applied to front and back side of the headlight diaphragms. John
My question is can these be reconditioned or do they need to be replaced?
I don't know what the inside of the relays look like but if there are seals in there .... I guess they've dried up.
The headlights do go up and down when vacuum is manually applied to front and back side of the headlight diaphragms. John
Drifting
Joined: Jul 2006
Posts: 1,259
Likes: 154
From: Deplorableville Nebraska
Let's see here, lots of vacuum to the middle relay port, and not much coming out of the top & bottom ports. Classic case of original relay leakage syndrome. Your relays are shot. Most of the vacuum is being lost around the seal of the relay's internal pistons. The fix is to simply replace them, or you can get them rebuilt. Not many places rebuild these, and from a 74 there is not much value to them.
If you want to make sure they are bad, connect a short piece of spare hose and block the bottom port. Try to blow through the relay. You shouldn't be able to if the seals are good.
If you want to make sure they are bad, connect a short piece of spare hose and block the bottom port. Try to blow through the relay. You shouldn't be able to if the seals are good.
Pro
Joined: Nov 2013
Posts: 730
Likes: 37
From: Catoosa Okla
Willcox has an excellent vacuum headlight troubleshooting chart that's sure to isolate the issue. My 74 had 2 leaking relays and a leaking canister seal. Also, my vacuum hoses were in pretty rough dry rotted shape. I went ahead and went through the entire actuator assembly, cleaning, painting and a good lubrication. Works like brand new now!
Safety Car
Joined: Sep 2013
Posts: 4,355
Likes: 2,633
From: Draper Utah
A new relay is $25, and takes 10 minutes to replace. Why waste time messing with a bad/questionable one?
Personally I keep a spare vacuum relay around because they are cheap and swapping in a new one is the fastest and easiest way to see if a relay is bad. Your mileage may vary.
Personally I keep a spare vacuum relay around because they are cheap and swapping in a new one is the fastest and easiest way to see if a relay is bad. Your mileage may vary.
Thread Starter
Racer
Joined: Aug 2013
Posts: 480
Likes: 95
From: Georgetown Kentucky
Thanks everyone …. replacement was what I thought would be the answer but just want to get some experienced opinions.
Dave J … thanks for tip and I’ll try your tip on checking before I pull trigger on ordering.
Patro46 … yep Wilcox’s info was great but didn’t actually show how to test relays unless I missed that.
Iceaxe … I’ve had this ’74 for 32 years … not bad that I never had to replace these before so I don’t mind that part and it was interesting learning how it all worked finally.
Dave J … thanks for tip and I’ll try your tip on checking before I pull trigger on ordering.
Patro46 … yep Wilcox’s info was great but didn’t actually show how to test relays unless I missed that.
Iceaxe … I’ve had this ’74 for 32 years … not bad that I never had to replace these before so I don’t mind that part and it was interesting learning how it all worked finally.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
This is the first link I've posted from the new site.... You guys can't see this portion of the site yet.. but it's giving me a chance to see if things will be normal. 
Here is the vacuum chart, and the info on testing the relay both the pic and the video from the website.
I'm not real happy with my first search results either..
Here is the vacuum chart, and the info on testing the relay both the pic and the video from the website.
I'm not real happy with my first search results either..
Thread Starter
Racer
Joined: Aug 2013
Posts: 480
Likes: 95
From: Georgetown Kentucky
That's a really good drawing of the headlight vacuum system. The only difference on my '74 is the two (2) brass fittings label as "1" in your drawing are both actually located between the bumper brackets on the Vacuum Tank, about 4" apart. Thanks
Dave J ... both relays failed the test tip you provided. Thks
Dave J ... both relays failed the test tip you provided. Thks
Last edited by Jcpstrat; Apr 25, 2015 at 11:27 AM. Reason: Added addition info.
Racer
Joined: Jan 2014
Posts: 334
Likes: 6
Like Dave mentioned above, the relays can be deceiving. Here's how I tested mine:
https://www.corvetteforum.com/forums...s-of-pics.html
They were the culprit; they would move but not hold vacuum.
Good luck!
https://www.corvetteforum.com/forums...s-of-pics.html
They were the culprit; they would move but not hold vacuum.
Good luck!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Instructor
Joined: Oct 2014
Posts: 215
Likes: 12
From: Conyers Georgia
This is the first link I've posted from the new site.... You guys can't see this portion of the site yet.. but it's giving me a chance to see if things will be normal.
Here is the vacuum chart, and the info on testing the relay both the pic and the video from the website.
I'm not real happy with my first search results either..
Here is the vacuum chart, and the info on testing the relay both the pic and the video from the website.
I'm not real happy with my first search results either..
Quick question, is there a test I can do with to check to ensure I have the vacuum lines hooked up correctly to the the headlight switch, without pulling the dash to confirm. I am 99% sure I am right, but want to confirm. I installed new actuators and relays and the light open, but slow and then after sitting over night, they did not want to open the next day. Just your thoughts would be appreciated.
Racer
Joined: Apr 2012
Posts: 257
Likes: 0
Let's see here, lots of vacuum to the middle relay port, and not much coming out of the top & bottom ports. Classic case of original relay leakage syndrome. Your relays are shot. Most of the vacuum is being lost around the seal of the relay's internal pistons. The fix is to simply replace them, or you can get them rebuilt. Not many places rebuild these, and from a 74 there is not much value to them.
If you want to make sure they are bad, connect a short piece of spare hose and block the bottom port. Try to blow through the relay. You shouldn't be able to if the seals are good.
If you want to make sure they are bad, connect a short piece of spare hose and block the bottom port. Try to blow through the relay. You shouldn't be able to if the seals are good.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
I was gonna post that it is relay, not relay's, but I see they went to 2 relays for headlights in late '69 or '70.
what exactly was the reason for change to two relays? seems pretty redundant, you only need one right? it's not like you would ever want to raise just one and need to control them individually, or am I missing something?
just curious...
what exactly was the reason for change to two relays? seems pretty redundant, you only need one right? it's not like you would ever want to raise just one and need to control them individually, or am I missing something?
just curious...