Headlight vacuum question
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From: Scott La
Headlight vacuum question
After opening the system and letting air in it how long should it take, with engine running to completely get vacuum in the system to operate the headlights? BTW its a 77 vette
Melting Slicks
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I get about a 10 second window after parking to get them down.
And it's been that way since '78. To me that's "normal".
-W
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For you guys that cannot raise or lower the lights without the engine running- this means that you have a serious, non-stop vacuum leak that is affecting the A/F ratio to the cylinders near the vacuum port. 
Melting Slicks
Joined: Apr 2001
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From: Olmsted Falls, Ohio
with MikeThis is a not a hard job to replace all the vacuum lines in the headlight system. I have seen the little round filters (up near the cowl) cracked
and leaking air, seen a small pinhole in hoses. Sometimes a devil to track down, easier to replace them all instead of one-by-one.
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From: Southbound
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From: Crossville TN
Except for those vacuum lines that 'see' sunlight or extremely high heat, the vacuum lines themselves are rarely the problem with your vacuum system. The most probable causes for significant vacuum leaks are:
#1 vacuum hose(s) pulled off or left off of a fitting.
#2 seals that are internal to vacuum components (ie, headlight relays, wiper safety switch, etc) are worn out and leaking.
#3 defective components like the wiper door solenoid/valve (behind tach...'68-72 only) or the check valve in the vacuum feed line from the intake manifold.
#4 heater control head vacuum manifold leakage (#1-#3 all can apply here, too).
This all sounds really complicated, until you learn that anything that operates with vacuum is merely an "ON/OFF" switch...it either passes vacuum or it seals vacuum. So checking any vacuum component is as simple as applying vacuum and seeing if it seals or not. Troubleshooting vacuum systems is easier than on electrical system. You just need to buy a little booklet on how these systems work and how to diagnose them. A simple vacuum gauge is a 'must'; they are available at all auto supply stores.
#1 vacuum hose(s) pulled off or left off of a fitting.
#2 seals that are internal to vacuum components (ie, headlight relays, wiper safety switch, etc) are worn out and leaking.
#3 defective components like the wiper door solenoid/valve (behind tach...'68-72 only) or the check valve in the vacuum feed line from the intake manifold.
#4 heater control head vacuum manifold leakage (#1-#3 all can apply here, too).
This all sounds really complicated, until you learn that anything that operates with vacuum is merely an "ON/OFF" switch...it either passes vacuum or it seals vacuum. So checking any vacuum component is as simple as applying vacuum and seeing if it seals or not. Troubleshooting vacuum systems is easier than on electrical system. You just need to buy a little booklet on how these systems work and how to diagnose them. A simple vacuum gauge is a 'must'; they are available at all auto supply stores.
