Headlight Vacuum Again

[ftsoft]

I have read the previous posts on this problem, but I have some questions. I'm just getting the car back together after about 20 years (It's doing very well after a nearly complete engine rebuild). The headlights wouldn't stay put, so I started looking at the system and eliminating things and when I came to eliminating the cross member, voila, the headlights work. I drove around for awhile with the headlights up and while I didn't climb any hills, they didn't budge at all. So.. Do I need to cobble together another reservoir or can I just leave the direct connection? If I do need another reservoir, has anyone done this (I'd like some hints). Thanks.

Frank

[Galwaylotus]

If the frame vacuum reservoir is leaking it probably means a crack in the frame somewhere. Might be a good idea to sort that out as well as the vacuum.

[m750rider]

By reading your post, you must have an early non-fail safe version for the headlamps, so keeping them raised is pretty important.

You can use the direct connection, but I would want the added safety of a reservoir, and more volume than the tubing alone provides.

You can find exactly where in the system you are losing vacuum by using a Mighty-Vac tool to pull a vacuum on each component - check valve at the intake, reservoir, headlamp pull switch, tubing connections. Find out which one is leaking. But in addition to the reservoir, I wouldn't be surprised if you found the switch leaking also. It is easy to repair and make it hold vacuum.

My frame reservoir on my S4 also leaks, enough that my headlamps will raise in a couple hours of not running (fail safe model). My fix was to loop about 6' of tubing from the intake to the pull switch, effectively adding more volume to the system without going through the frame reservoir. With that set up, the lamps will stay down a couple days.

Use the Might-vac to check the frame reservoir and see how fast it loses vacuum. It only takes a small split to make it leak enough to affect the headlamps. I pressurized mine with a small compressor and I couldn't find a leak, but it wouldn't hold vacuum. It will likely not be anything you have to worry about structurally.

Other cars use vacuum reservoirs that you can adapt if you choose. Mercedes uses one on their older cars to handle central locking functions, you can adapt it to take the place of the frame. They are easy to find new and used.

Good luck

[andyhodg]

Hi
I had a similar problem and it turned out to be cracks in the cross member where the where the wishbone mounts are. It's more important to get the cracks repaired than worrying about the headlights. Although I know from experience that the headlamps suddenly drooping when driving down a dark lane is un nerving. If the crossmember is cracked make sure that whoever welds it knows what they are doing. The crossmember is full of petrol fumes.

Good luck
Andy

[ftsoft]

Thanks everyone who responded. Good advice that the frame might be compromised, Ill check that out. As far as the reservoir goes, it works better now without it than it has with it since 1971.

Frank

[billwill]

I've been thinking about that.

Surely it would only contain petrol fumes if the non-return valve failed. The carb end of the pipe sucks, not blows.

Bye the way, My vacuum system has never been perfect, It is the suck to pull up type and the lamp pods have never stayed up for more than about 10 minutes after the engine is switched off.

[paddy]

Surely it would only contain petrol fumes if the non-return valve failed. The carb end of the pipe sucks, not blows.

Yes, I wondered the same. I guess when the car is idle, with the reservoir "full of vacuum", there is gradual leakage (through the pods, the switch, and also presumably the non-return valve). This will also be happening all the time that the engine is running but the manifold vacuum is less than the current reservoir vacuum (which is most of the time). Any leakage through the valve will contain vapour and, over time, this must lead to some accumulation in the reservoir. The valve doesn't have to have failed to any discernable extent.

Paddy

[prezoom]

One other place to check. I did the vacuum test on every component and discovered the leak was in the switch itself. Took the switch apart and found the base area where the tubes enter the switch was far less than flat. Also the rubber pad, being 45 years old was less than supple. I draw filed the area around the tubes to make the entire base as flat as possible, a piece of sandpaper on a flat surface took care of the rubber pad, making it flat as well, and some rubber grease added around the rubber pad fixed the problem. Also shimmed the spring to make it stiffer. Non-failsafe lights will now stay up for just over 4 days after shutting off the engine.

Rob Walker
26-4889