Vacuum issue .

[Mad4slalom]

Hi all, out for a little blast last eve, had lights on 1st position, sidelights on , headlights down . I stopped to top up fuel, by the time I paid and came back to the car, I started up and started to drive out of the forecourt I noticed the headlamps came up unevenly, the wiper door sort of opened and closed and I could hear the astro ventilation flaps in the rear area opening and closing. I then drove off and they settled down and seem normal again now. I know the vacuum tank in the fender is supposed to hold enough vacuum for a couple of operations without motor running , I dont think mine has ever managed that so I think it had lost vacuum while i was refuelling and when I drove off immediately after re starting motor there was insufficient vacuum so the wiper door and lights tried to open as they fail open, by which time the motor had made more vaccum so everything closed again? Is my take on it a possibilty? Maybe a slight leak in head lamp switch ? as normal daytime driving i have no lights or sidelights on so issue of low vacuum doesnt show itself ? Any ideas or suggestions appreciated. TiA

 

[Chuffer]

Hi all, out for a little blast last eve, had lights on 1st position, sidelights on , headlights down . I stopped to top up fuel, by the time I paid and came back to the car, I started up and started to drive out of the forecourt I noticed the headlamps came up unevenly, the wiper door sort of opened and closed and I could hear the astro ventilation flaps in the rear area opening and closing. I then drove off and they settled down and seem normal again now. I know the vacuum tank in the fender is supposed to hold enough vacuum for a couple of operations without motor running , I dont think mine has ever managed that so I think it had lost vacuum while i was refuelling and when I drove off immediately after re starting motor there was insufficient vacuum so the wiper door and lights tried to open as they fail open, by which time the motor had made more vaccum so everything closed again? Is my take on it a possibilty? Maybe a slight leak in head lamp switch ? as normal daytime driving i have no lights or sidelights on so issue of low vacuum doesnt show itself ? Any ideas or suggestions appreciated. TiA

Firstly check the non return valve in the vacuum line to the manifold . It may half failed allowing air to slowly seep back into the system . If that checks out OK then check for leaks with a vacuum test kit , they are not expensive . The technical definition of a vacuum is `f**ck all in a pipe ` , so if you have more than `f**ck all ` in the pipe you have no vacuum !

 

[Emc]

Cut 1/2" off every hose you can find, the ends tend to swell over time

 

[Chuffer]

I don`t know how many inches of mercury the C3 draws in vacuum but another reason the vacuum system may loose it`s efficiency could be old and perished hoses that could collapse under normal atmospheric pressure of 14 psi .

 

[Roscobbc]

Typical vacuum reading 'at carb' should be between 15 to 18 or more HG........if you have a 'cam' perhaps as low as 10 -12 hg. This is where your vacuum accessories start to struggle - the headlamps will be slow lifting, if you have a wiper flap perhaps that too......power brakes will perhaps take a few minutes of the engine running to create enough vacuum in the reservoir........

 

[Mad4slalom]

Typical vacuum reading 'at carb' should be between 15 to 18 or more HG........if you have a 'cam' perhaps as low as 10 -12 hg. This is where your vacuum accessories start to struggle - the headlamps will be slow lifting, if you have a wiper flap perhaps that too......power brakes will perhaps take a few minutes of the engine running to create enough vacuum in the reservoir........

It has a street cam , no power brakes, I will take it out again and see if it is still playing up. When I first got the 72 , the headlights and wiper door would open once and then close on every start up. After a couple of years it suddenly stopped doing this and has been fine apart from the odd random event.

 

[Chuffer]

Typical vacuum reading 'at carb' should be between 15 to 18 or more HG........if you have a 'cam' perhaps as low as 10 -12 hg. This is where your vacuum accessories start to struggle - the headlamps will be slow lifting, if you have a wiper flap perhaps that too......power brakes will perhaps take a few minutes of the engine running to create enough vacuum in the reservoir........

Interesting figures Ross , I did not expect it to be as high as 18 HG or more . Most of my experience and training in vacuum operated systems is on steam locos ( needless to say ) because the braking systems are either fully vacuum operated at 24 ins HG on Great Western built locos or combined steam / vacuum at 21ins HG on other types . Being able to test and find faults in the complex systems was a crucial part of our training.
Those of us of a certain age will remember the erratic nature of vacuum operated wipers on Ford Prefects et al that nearly flew off the screen when you came off the gas !!

 

[Mad4slalom]

Cut 1/2" off every hose you can find, the ends tend to swell over time

Thanks gavin, should i put back dry or a bit of rtv as well?

 

[Roscobbc]

Interesting figures Ross , I did not expect it to be as high as 18 HG or more . Most of my experience and training in vacuum operated systems is on steam locos ( needless to say ) because the braking systems are either fully vacuum operated at 24 ins HG on Great Western built locos or combined steam / vacuum at 21ins HG on other types . Being able to test and find faults in the complex systems was a crucial part of our training.
Those of us of a certain age will remember the erratic nature of vacuum operated wipers on Ford Prefects et al that nearly flew off the screen when you came off the gas !!

Back in the 50's and 60's vacuum operated items in American cars was quite the norm (or hydraulically operated like Cadillac). I recall the 1966 Galaxie 428 4 speed coupe I owned.... whilst having 'manual' wind-up windows all around.......it had vacuum operated internal door locks for the two rather large doors, seat-back releases for the front individual bucket seats and the 'airflow' ventilation extraction flap on the rear deck (much like earlier C3 Vettes....but 'powered'). Those vacuum operated items (like our headlights and wiper flaps) are surprisingly powerful.

 

[antijam]

Although the use of vacuum for ancillary operation on cars has diminished since the '70's, vacuum operated linear motion actuators - such as those used for door locks - have traditionally been simpler, cheaper and more reliable than electrically powered alternatives. Some manufacturers, notably Mercedes-Benz, used vacuum for several mechanical functions from the '60's to well into this century. The Intake manifold vacuum initially used was replaced by a system of electrically powered vacuum and pressure pumps and on the later Mercedes PSE (Pneumatic System Equipment) the change from vacuum to pressure was obtained by simply reversing one pump. The vacuum/pressure PSE system on my old 2002 Mercedes R170 SLK was a great deal more complex than on my '71 'Vette, not only operating the central locking but the alarm, demister, interior light and several other systems as well.
Fundamentally very reliable, the systems Achilles heel on the SLK was that the PSE pump was located in the boot in an area where it could get wet and malfunction. If this happened you can well imagine the sort of havoc that ensued. Since so many things usually failed at once, diagnosis (and subsequent replacement of the PSE unit) was relatively easy.

 

[Mad4slalom]

Although the use of vacuum for ancillary operation on cars has diminished since the '70's, vacuum operated linear motion actuators - such as those used for door locks - have traditionally been simpler, cheaper and more reliable than electrically powered alternatives. Some manufacturers, notably Mercedes-Benz, used vacuum for several mechanical functions from the '60's to well into this century. The Intake manifold vacuum initially used was replaced by a system of electrically powered vacuum and pressure pumps and on the later Mercedes PSE (Pneumatic System Equipment) the change from vacuum to pressure was obtained by simply reversing one pump. The vacuum/pressure PSE system on my old 2002 Mercedes R170 SLK was a great deal more complex than on my '71 'Vette, not only operating the central locking but the alarm, demister, interior light and several other systems as well.
Fundamentally very reliable, the systems Achilles heel on the SLK was that the PSE pump was located in the boot in an area where it could get wet and malfunction. If this happened you can well imagine the sort of havoc that ensued. Since so many things usually failed at once, diagnosis (and subsequent replacement of the PSE unit) was relatively easy.

We used to run vw LT diesel vans and they had a vacuum pump run off the cam for , I presume , brake servo vacuum, I think a spring kept a pushrod in constant contact with the camshaft but would stick on over run approaching junctions etc and you would get a horrendous clacking metal on metal tapping similar to a stuck hydraulic lifter , Scared the hell out of me first time it happened.!

 

[Emc]

Thanks gavin, should i put back dry or a bit of rtv as well?

Dry

 

[Mad4slalom]

Update, I now have the use of a decent vacuum pump, I have disconnected the vac pipe between the manifold and the vac filter. Watching a youtube video it shows a guy connecting the vac pump to the hose and then after switching on pump , going around all bits of the vacuum system listening for air leaking.
When discussing this casually with a friend , he said ,”you will struggle to hear a leak with a vacuum pump” and that i would be better pressurising vac system with a foot pump. ? Any thoughts appreciated on rights or wrongs .

 

[teamzr1]

If you used a spray bottle with soapy water while having a vacuum, you could see bubbles where leaks are ?
Better would be using a smoker

 

[Chuffer]

If you used a spray bottle with soapy water while having a vacuum, you could see bubbles where leaks are ?
Better would be using a smoker

That`s a new one on me .. looking for bubbles being sucked in and not blown out !!!!

 

[Mad4slalom]

If you used a spray bottle with soapy water while having a vacuum, you could see bubbles where leaks are ?
Better would be using a smoker

Would’nt that suck the liquid “into” the vacuum not “blow” bubbles out ? Have used that method to test for gas leaks.

If you used a spray bottle with soapy water while having a vacuum, you could see bubbles where leaks are ?
Better would be using a smoker

That`s a new one on me .. looking for bubbles being sucked in and not blown out !!!!

That was my thoughts too .

 

[Roscobbc]

You'd see the soapy bubbles being drawn-in by the vacuum tube (or 'not' if you don't have a damaged/perished section)

 

[teamzr1]

That`s a new one on me .. looking for bubbles being sucked in and not blown out !!!!

Very few bubbles (not water) would get pulled in and being that area than would be needing repair there would be no issues with those bubbles

Instead, use like 5-10 PSI from an air compressor or hand pump and lightly spray the soapy water would find leaks

 

[Mad4slalom]

Very few bubbles (not water) would get pulled in and being that area than would be needing repair there would be no issues with those bubbles

Instead, use like 5-10 PSI from an air compressor or hand pump and lightly spray the soapy water would find leaks

I connected up the vac pump this eve . As vacuum built, the lights and wiper door opened as they do on every start up and closed again I can pull down on the over ride switches and they operate as intended. . I have’nt tried the bubblemix yet but couldnt hear any leaks. Maybe try bubbles then pressurising with air. I was hoping that some vette owner somewhere would have had the exact same issue and could have said what was causing it. Weird that everything works as it should , except for the opening / closing on startup. Plus the fact it corrected itself once and has been fine for 2 years !
Any suggestions

 

[teamzr1]

Where did you insert your vacuum pump ?
How much pressure was the pump creating ?

Could it be higher than what the vacuum system has from the engine
and if so, maybe you overcome the problem with higher vacuum pressure ?
Do both headlight doors act the same ?

Do you have a C3 service manual ?
If not the oldest this website has is 1982 but should do and is complete service manual download it here :

Free Service Manuals for Chevrolet vehicles | Operation CHARM

Detailed repair/service/workshop manuals for many Chevrolet vehicles, including electrical diagrams, recommended bolt torques, and estimated labor times.

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