Headlight Trouble
Thread Starter
7th Gear
Joined: Dec 2006
Posts: 7
Likes: 0
Headlight Trouble
I know that the vacuum system for the corvette is prone to failure, but I checked the system and there is not a notable leak. The headlights move about 1/2 an inch and stop when turned on. When looking at the troubleshooting manual, I noticed that the engine is supposed to be making 18-20 inches of Mercury when measured directly from the manifold outlet. Throughout the entire system, I get 11 inches of Mercury. Is this low vacuum the cause of my headlights not going up (the manual said that some corvettes had a low vacuum) and if this is the problem, is there anything I can do to raise the vacuum level? Please help.
Instructor
Joined: May 2006
Posts: 223
Likes: 1
From: Kennesaw GA
The vacuum sounds low, but depending on your location and elevation, the cam you are running and how the car is tuned, that might be all you get. If the car is running properly, then you need to make sure the vacuum system is as good as it will get by checking your cannister and all associated relays for the headlights and wiper door depending on the year.
First off I would hook up a vacuum pump, like a Mitey Vac to the actuators on the headlights and see how much vacuum they take to open and close. You may just have some binding in the headlight mechanism that's causing the problem.
First off I would hook up a vacuum pump, like a Mitey Vac to the actuators on the headlights and see how much vacuum they take to open and close. You may just have some binding in the headlight mechanism that's causing the problem.
Race Director
Joined: Feb 1999
Posts: 19,659
Likes: 34
From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
11 inches should be enough to make them come up IMO. It will just make them slow. If you rev the motor does the vacuum come up?
I don't know which manual you are using to troubleshoot but here is a pretty good one that we all have been using for quite a while.
Look for the link on the left side of the page Vacuum Trouble.
I don't know which manual you are using to troubleshoot but here is a pretty good one that we all have been using for quite a while.
Look for the link on the left side of the page Vacuum Trouble.
Intermediate
Joined: Feb 2006
Posts: 46
Likes: 0
From: Tyler TX.
Headlight problems
Might want to check out the check valve to see if it's holding. It is a metal one-into-two disc looking thing located up by the firewall. If it's not holding as it should, the vacume is not 'building' enough to open the headlights.
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
mine acted similiar to yours on my 79, it was the rod seal on the main actuator, both were rotten, when they started to move they would start leaking and the headlight would only come up about 3", i installed new seals about $10 ea., fixed 
