Headlight vacuum relay question/thoughts
Thread Starter
Pro
Joined: Aug 2014
Posts: 508
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From: Oscoda Michigan
Headlight vacuum relay question/thoughts
I know there are some folks on here that were around in "the day" when this system was designed. So why two relays? I just replaced my drivers side because the old one leaked causing that side to be lazy. Just for grins and giggles I hooked the headlights up using the one good relay, worked fine and both worked at the same speed and time. Did they use two for safety so only one side might fail at a time or is there a more sinister reason lurking in the closet? Oh by the way I sure love my old corvette she has already provided hours and hours of thought and tinker time, wouldn't trade it for the world. Mike
Racer
Joined: Nov 2014
Posts: 463
Likes: 129
I know there are some folks on here that were around in "the day" when this system was designed. So why two relays? I just replaced my drivers side because the old one leaked causing that side to be lazy. Just for grins and giggles I hooked the headlights up using the one good relay, worked fine and both worked at the same speed and time. Did they use two for safety so only one side might fail at a time or is there a more sinister reason lurking in the closet? Oh by the way I sure love my old corvette she has already provided hours and hours of thought and tinker time, wouldn't trade it for the world. Mike
I don't know the reason why two relays, but the system was not originally designed that way. 1968 Corvettes only had one relay. The second relay was added in 1969.
John
Heel & Toe
Joined: Dec 2013
Posts: 24
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My car from -69 has one relay. I have noticed that the right light opens some secunds after the left one. Lengths of the hoses????? The hoses to the right side are longer.
I dont know. I am not sure.
Greatings from Sweden Lennart B
Restoring a -69 conv (early) to original shape.
Racer
Joined: Nov 2014
Posts: 463
Likes: 129
Hey
My car from -69 has one relay. I have noticed that the right light opens some secunds after the left one. Lengths of the hoses????? The hoses to the right side are longer.
I dont know. I am not sure.
Greatings from Sweden Lennart B
Restoring a -69 conv (early) to original shape.
My car from -69 has one relay. I have noticed that the right light opens some secunds after the left one. Lengths of the hoses????? The hoses to the right side are longer.
I dont know. I am not sure.
Greatings from Sweden Lennart B
Restoring a -69 conv (early) to original shape.
Doing more research it looks as if it was 1970 was the year when the second relay was added.
The length of the hoses should be kept as close as possible to have the headlights open together, but I think a bigger factor is the condition of vacuum system and the actuators. Leakage in ether of these would cause them to not go up and down together.
On my 1968 the headlights didn't go up and down together. I just had the actuator re-plated and the seals replaced to see if that solves my problem. I haven't had time to install them yet to test.
John
Heel & Toe
Joined: Dec 2013
Posts: 24
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Lennart
Doing more research it looks as if it was 1970 was the year when the second relay was added.
The length of the hoses should be kept as close as possible to have the headlights open together, but I think a bigger factor is the condition of vacuum system and the actuators. Leakage in ether of these would cause them to not go up and down together.
On my 1968 the headlights didn't go up and down together. I just had the actuator re-plated and the seals replaced to see if that solves my problem. I haven't had time to install them yet to test.
John
Doing more research it looks as if it was 1970 was the year when the second relay was added.
The length of the hoses should be kept as close as possible to have the headlights open together, but I think a bigger factor is the condition of vacuum system and the actuators. Leakage in ether of these would cause them to not go up and down together.
On my 1968 the headlights didn't go up and down together. I just had the actuator re-plated and the seals replaced to see if that solves my problem. I haven't had time to install them yet to test.
John
With best regards
Lennart B
I Think the vaccum can be the problem. I have a carburator from Edelbock,?????? ///LennartB
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
the carb has nothing to do with the vacuum, you should be coming straight off the intake.
Also, it's tough to get them to open and close exactly the same, length of hose won't matter, vacuum at one end is the same at the other. friction won't be a factor at the low flow we're talking about with these.
what happens is, parts get replaced. no 2 valves, relays, etc. are going to be the same unless made with the same parts and same spec.
I've got a bunch of relays, and they all work at different rates due to how much lube was used when it was made, age/how stiff it got, etc. In fact, one of them is brand new (bought a setup from a guy on here) and it leaks around the housing where it wasn't crimped tight enough...point is, there is a lot of variation in the materials and assembly/tolerances of these things. vacuum is the least of it...
Heel & Toe
Joined: Dec 2013
Posts: 24
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Yep, this is why. Originally they had one (my '68). they went to two seperate relays so at least one would work.
the carb has nothing to do with the vacuum, you should be coming straight off the intake.
Also, it's tough to get them to open and close exactly the same, length of hose won't matter, vacuum at one end is the same at the other. friction won't be a factor at the low flow we're talking about with these.
what happens is, parts get replaced. no 2 valves, relays, etc. are going to be the same unless made with the same parts and same spec.
I've got a bunch of relays, and they all work at different rates due to how much lube was used when it was made, age/how stiff it got, etc. In fact, one of them is brand new (bought a setup from a guy on here) and it leaks around the housing where it wasn't crimped tight enough...point is, there is a lot of variation in the materials and assembly/tolerances of these things. vacuum is the least of it...
the carb has nothing to do with the vacuum, you should be coming straight off the intake.
Also, it's tough to get them to open and close exactly the same, length of hose won't matter, vacuum at one end is the same at the other. friction won't be a factor at the low flow we're talking about with these.
what happens is, parts get replaced. no 2 valves, relays, etc. are going to be the same unless made with the same parts and same spec.
I've got a bunch of relays, and they all work at different rates due to how much lube was used when it was made, age/how stiff it got, etc. In fact, one of them is brand new (bought a setup from a guy on here) and it leaks around the housing where it wasn't crimped tight enough...point is, there is a lot of variation in the materials and assembly/tolerances of these things. vacuum is the least of it...
When I check the system after the change of sealings and the hoses. I put the vaccum on both sides of the actuators for 5 minutes and no loss of vaccum. Goasts or??????????
Lennast B
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Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
places the actuators leak: inner diaphragm, outer seal, rust pinholes through the steel housing (extremely common and often overlooked).
the relays leak internally through bottom with bad o-rings or warn housing, tears in the main diaphragm, or improper crimp of the metal to plastic connection. the bottoms of the relays are open to the atmosphere, and should have a felt or foam filter. they go missing, bugs and dirt get up in there and ruin the o-ring and sealing area.
the entire headlight system is out in front getting hit with the weather, rain, bugs, etc. although the vacuum design is sound, the execution was not the greatest...
hope this helps.
Heel & Toe
Joined: Dec 2013
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Greating from Sweden Lennart B
Safety Car
Joined: Oct 2007
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From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
I only installed 1 relay, this way they raise up and down at the same time,
thought it was a waste to connect two relays for the same job.
Redundancy is for the space shuttle, not my weekend joy ride.
thought it was a waste to connect two relays for the same job.
Redundancy is for the space shuttle, not my weekend joy ride.