Vacuum query .. Again!

[Mad4slalom]

Evening All, I have one for all the vacuum afficianados ! Now I have had a situation since I had the 72 where on every start up my headlamps and wiper door would open and then close again. For the first year I just presumed that this was testing the system. It all worked properly using the headlamp switch and or the h/lamp and wiper door overide switches under the dash. When I finally realised that the opening and closing on startup was not actually supposed to happen I tried various things , filter / check valve, loose or split hoses but nothing was apparent. Now , Here’s the thing, I started up the vette for a run this eve and was suddenly aware that the hlamps and wiper door did not open and close. They work properly via the hlamp switch and over rides and for the last four or five start up’s have not opened and closed. My passenger side headlamp had also started to lag behind the drivers side lamp by about 5-8 seconds, this seems to have caught up now. I havent really touched anything, anyone have any ideas as to what may have changed to cause this .? Fingers crossed it carries on behaving itself.

 

[Roscobbc]

My thoughts would be to begin with basic's - firstly check for vacuum leaks, so vacuum reservoir first and simply follow the vacuum lines and motors. Even though vacuum piping many not appear damaged, like tyres the tube can develop micro-cracks which may only leak at specific low - or high under-hood or cabin temperatures. Bends are agood place to start. Ideally it would be ideal to test the vacuum installation without the engine running and a full (er' 'empty') vacuum tank and a 'sharp' ear.......but you won't have too much time!

 

[Mad4slalom]

My thoughts would be to begin with basic's - firstly check for vacuum leaks, so vacuum reservoir first and simply follow the vacuum lines and motors. Even though vacuum piping many not appear damaged, like tyres the tube can develop micro-cracks which may only leak at specific low - or high under-hood or cabin temperatures. Bends are agood place to start. Ideally it would be ideal to test the vacuum installation without the engine running and a full (er' 'empty') vacuum tank and a 'sharp' ear.......but you won't have too much time!

Thanks rosscob, do you think they were opening because the vac tank had emptied when motor was switched off. So next time it was started they went to default “open” position , then , as the motor built vacuum again they closed and worked as normal, Until the next time the motor was switched off and the vac tank would drain again . This cycle would then just repeat over and over. The only thing is that even if i switched off and started again instantly they would still do it even though in that moment the vac tank should still have had some pressure. Maybe just see how long it carries on working properly rather than disturb something and it reverts back to the opening issue 🫣

 

[Emc]

You definitely have a vac leak

 

[Mad4slalom]

Hi gavin, this is what is baffling , I must have “Had “ a vac leak, but do I “Have” a vac leak at this moment? As it is all working properly. I switched out the filter and check valve you sent me just to eliminate them and made no difference at the time. I just wonder what has changed, can a hose leak seal itself ? the other thing that may be just in my head is if I have vacuum advance and i was losing vacuum somewhere , would that affect the running? Its just that the car seems to be accelerating more smoothly now the lights and door are not opening on start up. I will test again today and report back.tho I am half expecting the situation to revert back to the opening and closing . Even if it does tho it gives me hope that it is just a leak and will really try to find it. The only thing I have been using more than usual is the headlight overide pull switch so whether that Was the source of the leak and has sealed from use ? , what do folk think? thanks for help

 

[CaptainK]

I love it when things self fix themselves. Nice one.

My wiper door on my 68 opens a tiny fraction and then closes when I first start the car. Like you originally I thought nothing of it until I discovered it meant it was a vac leak. I keep forgetting about it as its not that obvious and I don't drive the C3 that often. So I forget to diagnose it. My plan was to cap off all the vacuum areas to limit down which pipe etc it is. I think it is just the wiper vac system. I have also been having naughty thoughts of getting an electric wiper conversion kit (and also electric headlight kit) - mostly because I don't choose to drive the car in the dark or rain, so I hardly ever use the lights or wipers. So the "on demand" usage of electrics seems ideal.

 

[Mad4slalom]

I love it when things self fix themselves. Nice one.

My wiper door on my 68 opens a tiny fraction and then closes when I first start the car. Like you originally I thought nothing of it until I discovered it meant it was a vac leak. I keep forgetting about it as its not that obvious and I don't drive the C3 that often. So I forget to diagnose it. My plan was to cap off all the vacuum areas to limit down which pipe etc it is. I think it is just the wiper vac system. I have also been having naughty thoughts of getting an electric wiper conversion kit (and also electric headlight kit) - mostly because I don't choose to drive the car in the dark or rain, so I hardly ever use the lights or wipers. So the "on demand" usage of electrics seems ideal.

Thanks captain, mine again today seems to be working properly, there is still sometimes a little movement of the wiper door but only a tiny bit where as it fully opened and closed every startup before. The headlights are still staying closed on start up and working perfectly via the switch. The sluggish passenger side one has also caught up again with the drivers side . Fingers crossed they stay working as they are. Still dont know after 2 and a half years why they have fixed themselves 🫣.

 

[teamzr1]

Was there not, if I recall a position of the light switch GM designed a vacuum position so that in cold weather to prevent the headlights
and cowl for wipers, to open ad stay open so that they would not freeze up ?

Someone needs to look in, like a 1972 owner's manual, and see if that function exists ?

 

[Mad4slalom]

Was there not, if I recall a position of the light switch GM designed a vacuum position so that in cold weather to prevent the headlights
and cowl for wipers, to open ad stay open so that they would not freeze up ?

Someone needs to look in, like a 1972 owner's manual, and see if that function exists ?

No , not in the headlamp switch , that is the function of the override switches for headlamps and wiper door , they are the two pull down switches below the steering column. These are and always have worked, the original issue was that the lights and wiper door would open and then close once on every start up.