Head light vacuum?

[Bill E.]

Hello all, how long after the engine is shut off should the head lights still retract on a 1974? If not right away where do I start to look for vacuum leaks? Thanks, Bill

[Edward J.]

Re: Head light vacuum?

Bill, I don't think anyone has timed how long the headlamps will work after shut down, everything is relative to how well the headlight relays and actuators are sealed,along with vaccum hose connection & integrity, check valve sealing also. on a 30+ year old car I would say you'd be lucky to see 45 sec.

The best way to check integrity of the system is a smoke machine which is generally a automotive shop type tool, it emmits smoke in the system and if there a leak, smoke will billow out that area.

[Joseph K.]

Re: Head light vacuum?

I agree with Edward but I am not familiar with the smoke tool. If it is a pressure system be very carefully pressurizing a vacuum system. It could be very tricky. Not sure if its recommended on some of the parts because they are made to work with vacuum.

[Michael W.]

Re: Head light vacuum?

Any tool that introduces pressure into a vacuum system will not replicate actual operating conditions. Many of the major vendors sell troubleshooting guides that will quickly isolate the faulty components. Some of these guides are available on line at no charge IIRC.

[Edward J.]

Re: Head light vacuum?

Guys the smoke machine is a great tool to traced out vaccum leaks, vac. hose connection problems in a headlamp or wiper door system, it is a machine that has a built in pressure regulator and emmits smoke into the system to locate a leak,and we all know how difficult that can be with c-3 cars.

I use this machine at my automtive shop on a daily basis,which is great also for new car fuel evaporation leaks.

[Harmon C.]

Re: Head light vacuum?

The relays have leaked on most systems I have checked out. For a PV I would want at least 15 minutes for the lights to open. I would ask the team leader what he wants because if the system is perfect it will hold an hour or more.

[Bill E.]

Re: Head light vacuum?

On a good day the vacuum system on my car will hold for about 5 seconds so I've got some work to do. Bill

[Randall K.]

Re: Head light vacuum?

Bill - I found on my '72 (while working on other heating/cooling issues) that I had multiple vacuum actuator and vacuum relay failures, so check them all - including the heating/cooling and wiper door parts. The guide from Doc Rebuild is an excellent tool for troubleshooting the system and for testing individual components. A handheld vacuum pump (brake bleeder) is essential. I use a vacuum pump (AC evacuation pump) for system testing.

Good luck!
Randy

[Michael W.]

Re: Head light vacuum?

Here is one of the best troubleshooting guides:

http://www.corvette-101.com/vacuum.htm

[Michael D.]

Re: Head light vacuum?

A My-T-Vac tool is handy.

[Bill E.]

Re: Head light vacuum?

Here is one of the best troubleshooting guides:

http://www.corvette-101.com/vacuum.htm

Michael, thanks for the troubleshooting guide, I'll start working my way through the tests. Bill

[Michael W.]

Re: Head light vacuum?

Glad it's of use. Don't be surprised if you find a multitude (veritable plethora for Chuck G) of leaks and check each component for function as well as being air tight. If the relays are original, they also may be slow in reacting due to dried grease on the sliding piston. Remove the filter on the bottom and give the exposed end of the piston a quick shot of silicone spray.