How much vacuum for headlights
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
How much vacuum for headlights
I know the vacuum system has been dealt with ALOT. But...
I had a leaky vacuum reservoir and by past it and the headlights worked fine, a little slow, but not bad. Tested the new tank ... no leaks, installed it and now the lights barely move and never come all the up. I have tuned the 350/350 to Lars's specs (runs great). According to my vacuum gauge, I am only pulling 10 psi at the connection to the manifold. Could that be my problem?
If I had hair, I'd pull it out!
I had a leaky vacuum reservoir and by past it and the headlights worked fine, a little slow, but not bad. Tested the new tank ... no leaks, installed it and now the lights barely move and never come all the up. I have tuned the 350/350 to Lars's specs (runs great). According to my vacuum gauge, I am only pulling 10 psi at the connection to the manifold. Could that be my problem?
If I had hair, I'd pull it out!
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Mine will come up at 10" of vacuum, so probably not your problem, at least not all of it.
If you idle it up to 1500 to 2000 do your headlights come up then and what is your vacuum at that point? If you have a stock engine then you should have at least 17" or so of vacuum at idle.
If you idle it up to 1500 to 2000 do your headlights come up then and what is your vacuum at that point? If you have a stock engine then you should have at least 17" or so of vacuum at idle.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
Mine will come up at 10" of vacuum, so probably not your problem, at least not all of it.
If you idle it up to 1500 to 2000 do your headlights come up then and what is your vacuum at that point? If you have a stock engine then you should have at least 17" or so of vacuum at idle.
If you idle it up to 1500 to 2000 do your headlights come up then and what is your vacuum at that point? If you have a stock engine then you should have at least 17" or so of vacuum at idle.
I've been looking at the post "How your vacuum system works" Figure 4 has got me confused. Figures 2 and 3 refer to a vacuum tank, but figure 4 says "To Air Tank". Any idea what is meant by that?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
The headlight system is one of the items on mine I have not had to work on so far. So I'm not the guy to tell you where exactly to look.
I would start by tracing out hoses and see if I have a serious leak somewhere. It sounds like that could be a problem. Either that or the headlight actuators themselves.
If 20" won't bring them up then you have a significant loss of vacuum somewhere along the line or at the end of the line (actuator).
I would start by tracing out hoses and see if I have a serious leak somewhere. It sounds like that could be a problem. Either that or the headlight actuators themselves.
If 20" won't bring them up then you have a significant loss of vacuum somewhere along the line or at the end of the line (actuator).
Drifting
Joined: Jul 2006
Posts: 1,259
Likes: 154
From: Deplorableville Nebraska
The author used his 3 illustrations, and the fourth is from another source. In his case, vacuum tank and air tank are interchangeable, or the same thing.
Ten lbs of vacuum is more than enough to operate your headlights, that is if they are not leaking. You need to check each component for leaks. Are your actuators and relays original?
Ten lbs of vacuum is more than enough to operate your headlights, that is if they are not leaking. You need to check each component for leaks. Are your actuators and relays original?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
The headlight system is one of the items on mine I have not had to work on so far. So I'm not the guy to tell you where exactly to look.
I would start by tracing out hoses and see if I have a serious leak somewhere. It sounds like that could be a problem. Either that or the headlight actuators themselves.
If 20" won't bring them up then you have a significant loss of vacuum somewhere along the line or at the end of the line (actuator).
I would start by tracing out hoses and see if I have a serious leak somewhere. It sounds like that could be a problem. Either that or the headlight actuators themselves.
If 20" won't bring them up then you have a significant loss of vacuum somewhere along the line or at the end of the line (actuator).
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
The author used his 3 illustrations, and the fourth is from another source. In his case, vacuum tank and air tank are interchangeable, or the same thing.
Ten lbs of vacuum is more than enough to operate your headlights, that is if they are not leaking. You need to check each component for leaks. Are your actuators and relays original?
Ten lbs of vacuum is more than enough to operate your headlights, that is if they are not leaking. You need to check each component for leaks. Are your actuators and relays original?
Thanks for the input.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
The actuators and relays are not original, but I don't know how old they are. I've had the car for 6 years. Looks like I will go through the entire system. The part that's really getting me is the fact that they worked when I bypassed the old vacuum tank and now don't work with the new vacuum tank. One giant step BACKWARDS!
Thanks for the input.
Thanks for the input.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Here's the link that your looking for.
The author goes into great detail about how the system works.
https://www.corvetteforum.com/forums...tem-works.html
Inside his write up is a troubleshooting guide on how to test each part.
http://www.corvette-101.com/vacuum.htm
The author goes into great detail about how the system works.
https://www.corvetteforum.com/forums...tem-works.html
Inside his write up is a troubleshooting guide on how to test each part.
http://www.corvette-101.com/vacuum.htm
Pro
Joined: Oct 2011
Posts: 554
Likes: 82
From: San Jose CA
Here's the link that your looking for.
The author goes into great detail about how the system works.
https://www.corvetteforum.com/forums...tem-works.html
Inside his write up is a troubleshooting guide on how to test each part.
http://www.corvette-101.com/vacuum.htm
The author goes into great detail about how the system works.
https://www.corvetteforum.com/forums...tem-works.html
Inside his write up is a troubleshooting guide on how to test each part.
http://www.corvette-101.com/vacuum.htm
Wow that is one heckuva resource, thanks Peterbuilt!
Last edited by Jim__H; Feb 18, 2015 at 01:19 AM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Measuring 10"Hg at the manifold port (when idling) doesn't mean that 10"Hg is all your engine will make. You could have lots of little leaks in the system that cause it to drop significantly [without having a major leak]. To know what vacuum your engine is capable of making, you need to remove and plug off ALL the vacuum system lines from the manifold (except for vacuum advance can) and THEN make your measurement. If you get significantly more than 10"Hg, you have some leaks.
The most common place for leakage, when you have headlamp opening problems, is worn vacuum relays at the headlamps.
The most common place for leakage, when you have headlamp opening problems, is worn vacuum relays at the headlamps.
....Start with know good base Vacuum. Disconnect all Vacuum lines.