Vacuum Systems 101 - Into The Void, Part One

How To Repair Your '68-82 Corvette's Headlight And Windshield Wiper Door Vacuum System

Rob Wallace III Dec 1, 2002 0 Comment(s)
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Do your C3's headlights spring to the ready like healthy Olympic all-stars, or do they seem sluggish, lethargic, and lagging?

When it comes time to wake up the lamps, or hit the windshield wipers on a '68-72 Stingrays, does it seem like your Vette needs a strong coffee I.V.? As many C3 owners can undoubtedly attest, slow headlamps are a problem that plagues many Sharks. It is a very common affliction, but that makes it no less frustrating.

Sometimes, the simplest questions receive the most complicated answers. That is most certainly the case with the opening and closing of the headlamps on all '68-82 Corvettes, and the windshield wiper door through 1972. These relatively minor functions are operated by one of the most complex, convoluted, and downright bewildering systems in the entire car.

The headlamps and windshield wiper door are operated by an extremely intricate vacuum system which utilizes suction created in the intake manifold by the running of the engine. Through a series of vacuum reservoirs, actuators, controls, and many, many meters of hoses, we get the seemingly straightforward rotation of our headlights. In the early (through 1972 model) Sharks, this vacuum is also drawn upon to open and close the panel that hides the windshield wipers.

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This book is indispensable if you own a '68-82 Corvette and do any of your own servicing and repairs.

Unfortunately, the fact that this vacuum system is so complex also means that there are a great number of things that can go wrong. There are inherent limitations, even in a perfectly functioning vacuum system. As soon as the engine is turned off, it stops creating the vacuum and the negative air pressure in the reservoirs begins to bleed off. That means that you'd probably have to restart the motor if you accidentally forgot to turn off the lights before you shut it off-unless you acted within the first few seconds and the vacuum system is in excellent condition.

But, unless the vacuum system has been repaired or replaced fairly recently, its pretty likely it isn't operating at its best. The process depends upon maintaining a completely airtight seal which deteriorates over time. The depressurizing and pressurizing of the system every single time the car is turned on and off puts a great deal of stress on the many parts. In a 20- to over 30-year-old Vette, which can easily equate to tens of thousands of depressurization cycles, that gradually take their toll on the components. The repeated contraction and expansion over time causes a lot of stress, and can create numerous holes, cracks, and leaks in the lightweight sheetmetal parts without even considering the life span or aging process of the numerous rubber hoses.

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Are you confused yet? The chart, with instructions on the back side, makes it relatively easy to re-plumb the vacuum hose system.

Without a strong vacuum, the headlight's actuation begins to slow down, individually and/or in unison, until finally they just don't have the "oomph" to open or close completely-or maybe at all. In a weakening '68-72 system, with the wiper door also drawing on the same overtaxed vacuum system, it becomes even harder for the car to operate all those functions at once, or even within a few minutes of one another in some cases, and increasingly frustrating for the owner. Considering the amount of stress and the number of components in the system, it is amazing that there aren't more problems.

Our friend Loy McKenrick recently tore down his '72 Shark for some fresh paint. It's the first time in the 20-some years he's owned the car that it has been taken apart to this extreme, which made it the perfect time to freshen up the vacuum system as well. The vacuum system can seem pretty daunting to the uninitiated, but it is nowhere near as overwhelming as it seems. With a vacuum gauge and lots of patience, it is possible to test all of the system's branches and components to track down the precise areas of distress on your Vette. In Loy's case, with the whole system being 30-year-old assembly line installed pieces, he decided to replace the entire setup and ordered every available piece of vacuum system for both the headlamps and the wiper door from Mid America Designs.

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It helps a LOT that the hoses are color-coded.

There are a few parts of the vacuum system that are not being reproduced by anyone (that we are aware of) yet, most significantly the main vacuum reservoir on early Sharks, which is essentially a stamped light-gauge sheetmetal box that holds the vacuum for all the various subsystems, and had to be repaired rather than replaced. It is the heart of the vacuum system and had taken a major beating over the years, but Loy has managed to buy a few more good years of service from the reservoir.

In the following two parts of this series, we will take you along as Loy repairs and replaces the entire vacuum system in his '72. We will devote one part to resuscitating the headlamps and one to healing the windshield wiper door, but we will be addressing the vacuum system as a whole. The subsystems each work in basically the same manner; thus it should become increasingly easy to understand as we go along. So sit back and relax as Team VETTE delves into the Void!

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