1971 headlights

[Paul Young]

Greetings,

On returning from a road trip this weekend I was climbing a Colorado pass at about 10k feet when my headlights came up without any invitation or other stimulus. I was surprised and watched them and in about a couple of minutes they went back down. I was driving my 71 and I did't let up on the gas to coast or do anything different to get them to retract. Does anyone else have a simular experience and possibly a solution or should I consult a paraphsycologist? The headlights work fairly normal most of the time with a little delay because of low vaccuum. I am interested in solving this mystery if anyone knows why this happens. My wife reminded me that it happened one other time. Thanks in advance. Paul 5962

[Jack H.]

Re: 1971 headlights

'Dancing' headlight as well as wiper door is symptom of vac system leak. On older cars (I've got a '71 SB too and it lives in Colorado at 8930 feet) like these there can be a myraid of leak sources both in the engine compartment as well as in the cockpit. To put right, you need to trap & Kill ALL the leak sources, then replace vac check valve as well as in-line vac filter (white disk between check valve and intake nipple).

Lots has been said on how to/where to and you'll find articles in the archieves. Summary is:

(1) Understand the system which in your case is dual vac circuit

(headlight and wiper door) with some parallel path/interaction.

(2) This can be done pretty easily with a phamphlet some sell some

give away "Troubleshooting Vac System" -- avaliable from Dr.

Rebuild, Mid America, NCRS merchandise library and other

Corvette suppliers.

(3) 'Knee jerk' reaction is to 'gut' the factory original hoses

and replace 'em all. Not wise in my mind because repro hoses

have slightly different markings than factory originals AND,

depending on when your car was built there may be evidence of

the transition from headlamp washer to no-HL washer in your

original hose set.

(4) Most leaks in hoses happen at nipple connections and simply

removing, inspecting and cutting off a short portion to get

to fresh rubber solves.

(5) Cleaning all the hoses with a silicon based lubricant (like

WD-40) does wonders to rejuvinate the rubber.

(6) Most leaks lie in functional block components (vac relays,

vac motors). MANY can be fixed without having to discard

and replace the factory original component via replacement

accordian seals, plugs, Etc. available from many catalog

sources.

(7) You can shotgun the system and 'gut' original parts to cure,

or spend personal time/$ to understand, troubleshoot and

maintain what's there at reduced component cost in exchange

for your personal time....

[Jack H.]

Re: 1971 headlights

'Dancing' headlight as well as wiper door is symptom of vac system leak. On older cars (I've got a '71 SB too and it lives in Colorado at 8930 feet) like these there can be a myraid of leak sources both in the engine compartment as well as in the cockpit. To put right, you need to trap & Kill ALL the leak sources, then replace vac check valve as well as in-line vac filter (white disk between check valve and intake nipple).

Lots has been said on how to/where to and you'll find articles in the archieves. Summary is:

(1) Understand the system which in your case is dual vac circuit

(headlight and wiper door) with some parallel path/interaction.

(2) This can be done pretty easily with a phamphlet some sell some

give away "Troubleshooting Vac System" -- avaliable from Dr.

Rebuild, Mid America, NCRS merchandise library and other

Corvette suppliers.

(3) 'Knee jerk' reaction is to 'gut' the factory original hoses

and replace 'em all. Not wise in my mind because repro hoses

have slightly different markings than factory originals AND,

depending on when your car was built there may be evidence of

the transition from headlamp washer to no-HL washer in your

original hose set.

(4) Most leaks in hoses happen at nipple connections and simply

removing, inspecting and cutting off a short portion to get

to fresh rubber solves.

(5) Cleaning all the hoses with a silicon based lubricant (like

WD-40) does wonders to rejuvinate the rubber.

(6) Most leaks lie in functional block components (vac relays,

vac motors). MANY can be fixed without having to discard

and replace the factory original component via replacement

accordian seals, plugs, Etc. available from many catalog

sources.

(7) You can shotgun the system and 'gut' original parts to cure,

or spend personal time/$ to understand, troubleshoot and

maintain what's there at reduced component cost in exchange

for your personal time....

[Paul Young]

Re: 1971 headlights

Thanks Jack,

I do not want to gut my hoses and I will start looking as soon as I get the above mentioned booklet. Could it be affected by the low vacuum of too large a cam shaft? I seem to be over cammed if you will. Thanks in advance. Paul 5962

[Paul Young]

Re: 1971 headlights

Thanks Jack,

I do not want to gut my hoses and I will start looking as soon as I get the above mentioned booklet. Could it be affected by the low vacuum of too large a cam shaft? I seem to be over cammed if you will. Thanks in advance. Paul 5962

[Jack H.]

Re: 1971 headlights

Book you are getting will basically tell you to discount the intake manifold's specifc vac pressure. Use a vac meter, disconnect the system load from the intake, measure the head pressure and make that number your basis or 'T-zero' figure.

Now, progress along the vac path one component/branch at a time (knowing when/where there are parallel branches and treating/isolating accordingly) and look for places where you see more than a 2 psi absolute delta from your starting vac pressure. That branch/component is a high candidate for close up leak inspection.

Reason book doesn't give an absolute head pressure pass/fail spec is it changes from car to car (MY, options, etc.) as well as state of engine wear. Also, check valve in system (another high likelihood suspect) is supposed to stop backflow transients (high accel/decel perturbation in absolute vac pressure) leaving vac storage can as a buffer to ride out the transient. So even with a mildly aggressive cam, the storage container/check valve are still in the system to protect you.

Fact that you see 'dancing' or 'winking' components points toward marginal integrity of system which is divided into two functional paths -- control, and exercise. If a key headlight door control element is marginal (vac portion of headlamp switch, HL over ride switch under steering column, HL control relay(s) in nose), it can spradically mis-fire giving false 'turn-on/turn-off' dirrectives. Same goes for the main control vac supply feeding the HL vac motors, but leaks here would typically fail shut (HL's not opening/opening slowly) rather than fail open (pop up). GOOD LUCK!

[Jack H.]

Re: 1971 headlights

Book you are getting will basically tell you to discount the intake manifold's specifc vac pressure. Use a vac meter, disconnect the system load from the intake, measure the head pressure and make that number your basis or 'T-zero' figure.

Now, progress along the vac path one component/branch at a time (knowing when/where there are parallel branches and treating/isolating accordingly) and look for places where you see more than a 2 psi absolute delta from your starting vac pressure. That branch/component is a high candidate for close up leak inspection.

Reason book doesn't give an absolute head pressure pass/fail spec is it changes from car to car (MY, options, etc.) as well as state of engine wear. Also, check valve in system (another high likelihood suspect) is supposed to stop backflow transients (high accel/decel perturbation in absolute vac pressure) leaving vac storage can as a buffer to ride out the transient. So even with a mildly aggressive cam, the storage container/check valve are still in the system to protect you.

Fact that you see 'dancing' or 'winking' components points toward marginal integrity of system which is divided into two functional paths -- control, and exercise. If a key headlight door control element is marginal (vac portion of headlamp switch, HL over ride switch under steering column, HL control relay(s) in nose), it can spradically mis-fire giving false 'turn-on/turn-off' dirrectives. Same goes for the main control vac supply feeding the HL vac motors, but leaks here would typically fail shut (HL's not opening/opening slowly) rather than fail open (pop up). GOOD LUCK!

[Patrick H.]

Re: 1971 headlights

Paul,

Realize also that the Dr Rebuild guide differs from the MidAmerica/avail thru NCRS guide. The Dr Rebuild guide show you how to test each piece of your system, and I found it easier to use that the other guide which talks about specific vacuum levels. I own both.

Patrick

[Patrick H.]

Re: 1971 headlights

Paul,

Realize also that the Dr Rebuild guide differs from the MidAmerica/avail thru NCRS guide. The Dr Rebuild guide show you how to test each piece of your system, and I found it easier to use that the other guide which talks about specific vacuum levels. I own both.

Patrick