C3 1970 Headlight Vacuum Troubleshoot

[Don Justham]

Just ran new vacuum lines on my headlight vacuum system and the lights will not raise. Don't know if they worked before I changed the hoses so I dont think the hose are to blame. I have checked them and they are hooked up correctly. What are the steps to take in trouble shooting the vacuum system? Can I unhook certain hoses to see if there is any air flow? Please outline the trouble shooting steps if you would. Thanks

[Jack H.]

There are a number of threads...

in the archieves on this subject (troubleshooting Shark vac systems). It's not as easy as a quick check this/that answer.

Typically, you start with a booklet from one of the major catalog houses (Dr. Rebuild, Corvette Central, Mid America) and first understand how the system works. Realize there are TWO parallel vacuum circuits servo (vac that actually moves this/that) and control (vac that tells this/that when to open/close) and how they're routed. Then, you methodically go look for fault(s).

[steve principle]

Are you sure the hoses are hooked up properly? *NM*

[Michael W.]

Re: C3 1970 Headlight Vacuum Troubleshoot

Are you sure you have vacuum in the system? If nothing is happening at all, check the hose going to the intake manifold.

[Don Justham]

Re: C3 1970 Headlight Vacuum Troubleshoot

Went through the vacuum checks and there is vacuum at the actuator but I don't know if it is enough. Obviously it is not enough as it wont raise or lower the lights. Don't know what to do next.

[Patrick H.]

Re: C3 1970 Headlight Vacuum Troubleshoot

I'd bet odds it's the actuator relay that mounts under the nose of the car, one for each side.

BUT, before you go replacing parts, buy the two vacuum guides. One is from and sold by Dr. Rebuild. The other is marketed through MidAmerica and others, and is also sold through the NCRS store. Otherwise you could end up wasting a lot of money on unnecessary parts.

Patrick