Cormac87

I put an electric vacuum pump before the filter and check valve to get an overall picture. I noticed (with both headlights and wipers in the off position) I am getting two obvious areas leaking and wondered if this was normal. One is the left front headlight relay is taking in air at the relay’s filter. The right side one is NOT doing the same. I am assuming the leaking left relay is bad or going. This left headlight rises more slowly than the right.
The other area is the wiper door safety switch. I notice that the short hose that goes through the firewall and is an open hose/vents is also taking in air through the vent hose. Are both these normal or indications that both are bad?

Iceaxe

Your vacuum system should have no leaks and should be able to hold vacuum.

Cormac87

OK Thanks Iceaxe. I replaced both components right after posting the question, and made a big difference. Both headlights close identically. How long should I expect vacuum system hold vacuum after turning off the engine? 15 seconds, 15 minutes, 15 hours? Everything works as it should, but I suspect I still have very minor leaks, because it appears the system loses vacuum in 10-15 seconds after shutting engine. Try to establish a baseline target for repairs. Again, thanks.

CanadaGrant

My 69 which also has the wiper door holds vacuum for about 90 mins. One area that most people miss when rebuilding and installing new seals, relays/actuators and lines in the system is the small vacuum line off the funny little T fitting on the drivers side of the firewall in the engine compartment that goes to the heater/ defroster controls in the console and the time that vacuum will remain can depend on what position the controls on the console are left in. Later cars without all the wiper door stuff will (or should) hold vacuum for longer.

Iceaxe

I worked on chasing vacuum leaks in my 1970 for an entire year. I was eventually able to get my system to hold vacuum for a week, which many C3 owners considered impressive. YMMV

Cormac87

Grant, I often wondered about the vacuum controls for the heater/defroster as most diagrams do not show them. I have not studied that/those components nor looked for it. Would you mind taking a photo of the T location. My car is a 1972 convertible. Are the vent doors in the rear of the interior vacuum operated? As I learn vacuum system, I am working from the obvious to the non. Thanks for your time and input.

CanadaGrant

Here is a link to a good pic of an aftermarket fitting with a description of where it is. It supplies vacuum for the heater/vent controls and yes, the vents in the rear are also vacuum operated.
https://www.corvettecentral.com/c3-6...irewall-303303