Vacuum query,

[Mad4slalom]

Hi all, after realising that my wiper cowl. And headlamps are Not Actually supposed to open and close once every time the engine is started, I am in the process of trying to find a leak or faulty component. Perhaps someone here may have had similar symptoms and have an idea where to look.
I have as well as the opening and closing on start up, passenger side hlamp is slow to open and close.
If i pull down the headlamp over ride under the column the head lamps open but the wiper door opens as well.
If I pull down the wiper door over ride under the column just the wiper door opens.
If I pull out the headlight switch, the headlights And the wiper door open!
I disconnected the 3 lines to the vacuum storage tank and connected them together to by pass the tank but that made the headamps and wiper door open and close randomly and repeatedly!! So I reconnected the tank back to normal. The 72 had all new lines when rebuilt and all still look as new . Got to download some info to study but any suggestions as to where to start would be appreciated. I have checked filter and check valve and think they are good., I am guessing it is possibly an issue in a part of the system that affects bothe wiper door and headlamps ? TiA

 

[johng]

Afraid I can't help with the wiper door as my car doesn't have one. This file gives a good explanation of how the headlights work though. I'd say your first thing to check is the check valve. If that is letting by on the headlamp switch side then on start up you will have no vacuum to the control side of the relays so the headlamps will come up. As soon as vacuum builds up through the headlamp switch the relays will operate and the headlamps will go down. Alternatively you might have a small leak on the headlamp switch circuit which would have the same effect.

 

[Mad4slalom]

Afraid I can't help with the wiper door as my car doesn't have one. This file gives a good explanation of how the headlights work though. I'd say your first thing to check is the check valve. If that is letting by on the headlamp switch side then on start up you will have no vacuum to the control side of the relays so the headlamps will come up. As soon as vacuum builds up through the headlamp switch the relays will operate and the headlamps will go down. Alternatively you might have a small leak on the headlamp switch circuit which would have the same effect.

thanks I will take a look at that.,I thought the check valve felt good , maybe I will get one sent down to iliminate that and abfilter too.

 

[Corvetteville]

I believe this diagram is for a 72.

 

[Mad4slalom]

I believe this diagram is for a 72.

Yes, mine does have two overide switches under the steering column. The wiper door on does as it should and opens just the wiper door but the headlamp one , as well as opening the headlamps , Also opens the wiper door

 

[Chuffer]

Have you got a vacuum gauge and test kit Mad4 ? They are not expensive and I found it very useful tracking down leaks on my 1980 . I also found that my non return valve was not ` non returning ` and the filter was missing which didn`t help awefully much .

 

[Mad4slalom]

Have you got a vacuum gauge and test kit Mad4 ? They are not expensive and I found it very useful tracking down leaks on my 1980 . I also found that my non return valve was not ` non returning ` and the filter was missing which didn`t help awefully much .

thanks chuffer, yes I bought a mitie vac ready for this, looking at the diagram that corvetteville kindly posted I can see the door and the lights are linked by hoses to the check valve and the bulkhead relay? (I think) I still dont understand exactly how the system operates so will keep reading and checking for leaks etc and try to learn more. QUOTE="Chuffer, post: 45335, member: 189"]
Have you got a vacuum gauge and test kit Mad4 ? They are not expensive and I found it very useful tracking down leaks on my 1980 . I also found that my non return valve was not ` non returning ` and the filter was missing which didn`t help awefully much .
[/QUOTE]

 

[CaptainK]

Ah vacuum leaks. Fun times. I'm thinking mine might have a slight leak somewhere and I suspect its the wiper override switch under the dash. Both overrides work fine, the headlight one doesn't display a warning light (is it supposed to?), but the wiper ones does fine. But when I turn the wiper override off, for a wee bit it still stays faintly lit before then going out

Be interested to see how you get on.

 

[Mad4slalom]

Ah vacuum leaks. Fun times. I'm thinking mine might have a slight leak somewhere and I suspect its the wiper override switch under the dash. Both overrides work fine, the headlight one doesn't display a warning light (is it supposed to?), but the wiper ones does fine. But when I turn the wiper override off, for a wee bit it still stays faintly lit before then going out

Be interested to see how you get on.

Will keep you posted, gavin kindly gave me some things to try next. I wasnt even aware that the over ride switches lit up, I will have a look at mine , is that just when the lights are on or if the over ride switches are pulled without the lights on?

 

[teamzr1]

Have you tried to mix some water and soap in a bottle and spray the whole vacuum system down to see bubbles form
where leak is ?

 

[Mad4slalom]

Have you tried to mix some water and soap in a bottle and spray the whole vacuum system down to see bubbles form
where leak is ?

no , but a good plan ! thank you

 

[antijam]

Is a vacuum leak going to blow bubbles since it's sucking rather than blowing? Soapy water might seal a leak temporarily and if it was significant you'd get a change in engine note.

 

[CaptainK]

Will keep you posted, gavin kindly gave me some things to try next. I wasnt even aware that the over ride switches lit up, I will have a look at mine , is that just when the lights are on or if the over ride switches are pulled without the lights on?

On my 1968, when I pull the override switch for the wiper, a red warning light appears on the right hand side of the centre dashboard console (aka the bit above the radio) saying something like "Wiper Override". I don't get one when I use the headlight override. Bulb might have gone though.

 

[Mad4slalom]

On my 1968, when I pull the override switch for the wiper, a red warning light appears on the right hand side of the centre dashboard console (aka the bit above the radio) saying something like "Wiper Override". I don't get one when I use the headlight override. Bulb might have gone though.

you learn something every day, hadnt heard of that , I thought you meant the overide switch lit up, I have not not noticed this lamp but will check today .

 

[Chuffer]

Is a vacuum leak going to blow bubbles since it's sucking rather than blowing? Soapy water might seal a leak temporarily and if it was significant you'd get a change in engine note.

Absolutely not IMO . As you say , a vacuum leak is sucking not blowing so you won`t get bubbles .

 

[Roscobbc]

Absolutely not IMO . As you say , a vacuum leak is sucking not blowing so you won`t get bubbles .

If you do get bubbles you'll know something is seriously amiss. Irrespective of suck/blow if you try any vacuum assisted component once the engine has been running and 'charged' the vacuum tank up.........you'll stand a better chance of hearing any leak if you've sprayed a soapy water solution over key vacuum pipes and components. Best visually inspect every length of the rubber vacuum tubing for degrading and perishing by bending the tube.

 

[teamzr1]

Absolutely not IMO . As you say , a vacuum leak is sucking not blowing so you won`t get bubbles .

If not thinking there would be no air leaking out than use like a minivac (other side of it) or a low PSI set air compressor and push the air
from the hose where it connects to the block, and soapy spray would bubble at the point of leak
This way can test with engine off.

 

[Mad4slalom]

Afraid I can't help with the wiper door as my car doesn't have one. This file gives a good explanation of how the headlights work though. I'd say your first thing to check is the check valve. If that is letting by on the headlamp switch side then on start up you will have no vacuum to the control side of the relays so the headlamps will come up. As soon as vacuum builds up through the headlamp switch the relays will operate and the headlamps will go down. Alternatively you might have a small leak on the headlamp switch circuit which would have the same effect.

Took the 72 out today for a run and a wash. I noticed that the sluggish passenger side headlamp is not at all sluggish at 40miles an hour, but at idle or just over it is very lazy, if it is fine at speed and the actuator seal has a slight leak , would it still not be slow? The car does have a mild cam but nothing too choppy, could this cam reduce vacuum enough at idle or low revs to cause the issue?
After i turned off the motor the lights and wiper door opened once on residual stored vacuum but would not close again. ( until i started up and built up vacuum again) still have the issue of headlamps and wiper cowl opening and closing once on every start up.

 

[teamzr1]

The CAM grind will greatly affect low end idle to mid-range RPMs
Not seen as badly with older cars but much worse with the computer controlled engines of today as it adjusts
fuel and timing as what MAP/vacuum is reported

The part of the CAM grind that affects vacuum is the LSA (lobe separation)

Narrow/Tight LSA cams make excellent low-end torque and have a beautiful power curve.
But nothing comes without a cost, and idle vacuum suffers as LSA shrinks.
This causes the engine's street manners and tuning to become fickle.
A cam with a tighter LSA will require a looser torque converter, may not be able to run vacuum-assisted brakes, and doesn't play nice with fuel injection.
Also effects the line pressure of auto tranny and not too good auto shifts

That loopy idle that is universally loved, and part of the allure of a tight LSA cam, is actually misfire caused from a combination of exhaust dilution in the intake manifold and poor cylinder filling at idle.
It creates an unsteady manifold vacuum condition that, on a fuel-injected engine, confuses manifold air pressure (MAP) sensors, making it hard for them to regulate fueling.
The intake air control valve (IAC), which regulates idle speed, also has to work overtime and often attempts to "catch" the idle, but usually shoots high or low. These issues can often be worked through by an advanced tuner, but always present

This maybe why you see headlights open/close at low speeds and worse at idle since LSA of CAM
Also, can be with older parts, are stiffer and require more vacuum pressure

Some of this can be helped with a vacuum reserve canister installed
Here is an example of one

https://www.amazon.com/Competition-Cams-5200-Canister-Aluminum/dp/B00062YEJK

LSA Guide

LSA at a Glance​

Narrower LSA:

• Moves torque to lower rpm
• Increases maximum torque
• Narrow powerband
• Increase chance of engine knock
• Increase cranking compression
• Idle to mid-RPM vacuum and quality is reduced
• Valve overlap increases
• Decreases piston-to-valve clearance

Wider LSA:

• Raise torque to higher rpm
• Reduces maximum torque
• Broadens powerband
• Decrease chance of engine knock
• Decrease cranking compression
• Idle vacuum and quality is improved
• Valve overlap decreases
• Increases piston-to-valve clearance

 

[johng]

Took the 72 out today for a run and a wash. I noticed that the sluggish passenger side headlamp is not at all sluggish at 40miles an hour, but at idle or just over it is very lazy, if it is fine at speed and the actuator seal has a slight leak , would it still not be slow? The car does have a mild cam but nothing too choppy, could this cam reduce vacuum enough at idle or low revs to cause the issue?
After i turned off the motor the lights and wiper door opened once on residual stored vacuum but would not close again. ( until i started up and built up vacuum again) still have the issue of headlamps and wiper cowl opening and closing once on every start up.

I'd say you've got at least 1 and probably more leaks in your vacuum system and to find them all you will probably need to go around with your vacuum pump, test different parts of the system and keep isolating components until you find the leaks.
To start with I would pull off the hose from port C on Corvetville's diagram and connect your vacuum pump to this hose. You should be able to pull a vacuum (say 15 or 20 inches) and then it should stay there. If it does (and I suspect it won't) then put a cap on the non return valve port and the start the engine, the headlamp and washer doors should stay shut. Let us know how this goes.