C3 headlight vacuum

[Mike Ivanich]

C3 SLOW headlights question:

It takes 3 minutes for my headlights to come up - many of the vacuum components and all lines have been recently replaced. I have 18lbs of vacuum at the reservoir, only 8 lbs at the headlight actuators - I am trying to find out what the vacuum readings should be. Thanks.

[Jim T.]

Re: C3 headlight vacuum

Mike vacuum readings should be in inches of vacuum not pounds. There are some troubleshooting manuals available for the C3 vacuum system. I don't have any yet and don't have a solution to your 3 minute wait for the headlights to come up. Do they both come up at the same time in 3 minutes? You could get a vacuum loan a tool from Auto Zone and perform a leakdown test on your headlight vacuum motors and see if they are holding applied vacuum. If I had to wait that long for headlamps to come up I would pull down the underdash control and raise the headlights by hand before I started the car. They should stay up. C3 headlights can be operated manually very easily.

[Michael W.]

Re: C3 headlight vacuum

Sounds like one or both of the relays are leaking with that much of a loss. You should have very little drop in vacuum throughout the system.

[Harmon C.]

Re: C3 headlight vacuum

Mike I replace all relays. I have found them to be the cause of most system leaks. On old vettes they both always leak. I have a box full of leakers if someone knows a fix please post it. Second is the seal on the canister rod. I have yet to find a hose that cutting off a little won't fix it. If one buys a long hose at the hardware you can feed the vacumn from another car so you can hear the leaks. I use an air tank and A/C vacumn pump. Lyle

[Roberto L.]

Re: C3 headlight vacuum

Hello, on relay valves I use to open/uncrimp the metal ring which surrounds the upper metal cup. I use a suitable screwdriver and with patience I manage to separate the metal piece. Usually I found a broken rubber diaphragm. I repair it with a flexible bond, reassemble, recrimp the ring and the relay valve holds vacumm like a champ. But the ring bad finish will be clearly visible, so from the resto stand point, it's a low point. No problem in the hidden headlight valves but in some 69/70 like my 70 there is a relay valve very visible in the firewall...

Another problem is in the rubber piston, you may dissasemble it from the back and clean trying to restore the rubber flexibility to aim in the sealing. Other people have used small o-rings with good results, not my case I'd say...

Ok, if I lived in USA I would try to locate good valves, but living far from there (like Argentina) you need to check all options.

Roberto, NCRS #30019, RMC