Vacuum-Operated Wiper Door Woes
One thing is for sure, the 1968-1972 Corvettes had cutting-edge technology. A vacuum-mechanical headlamp and wiper door with fiber-optic bulb status was undoubtedly innovative. It was quite an accomplishment to get the wiper door to close and open in conjunction with the wiper arms swinging around.
Certainly, fail-safe switches were incorporated to prevent inadvertent closing of the wiper door on the wiper arms. With the smooth transition from hood to windshield, the wiper door makes the 1968-1972 Corvettes unique in appearance and function.
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Like our headlamp door res-toration story, the 1969’s wiper door was corroded and stuck in the closed position. The wiper door was stuck so badly that we removed the entire assembly to avoid breaking components. All of the wiper door linkage pivot points are plastic-bushed, and the corrosion made the bushings stick. Once you get the door linkage pieces out, you will realize that it took a lot of thought to make all these strange-looking linkage pieces to make the door move so smoothly. Our linkage was in decent shape except for the corroded pins and bushings. The pivot pins are actually job-specific rivets that require setting with a press or hammer to stake the pin in tightly. Another problem that we always encounter, no matter how well-maintained the ’68-’72 Corvette, is stuck wiper door to linkage screw-in pivot pin bolts. Wiper door screw-in pivot pin bolts corrode and then break as you try to remove them. We find at least one tight screw per wiper door, and this ’69 was no exception. All of the screws were tight and ready to break off. Every once in a while something goes right – in our case, discovering that tapping on the backside of the pivot screws to loosen them actually works. The idea is to tap on the backside of the screw to loosen the corrosion and allow the screw to release the threads.
Once all the pieces are apart, we can start the clean-up process and prep for paint. Before any final painting occurs, we will assemble the linkage and stake the pins in place. This avoids chipping and scratching the paint. After staking the pivot pins, we will paint all the linkage pieces with good-quality black epoxy paint. We have easier access before the linkage components are re-installed, so let’s move on to the vacuum system and installing the wiper arm switch and hoses.
A Systems Approach: The ’68-’72 wiper door vacuum system uses the same relay valve as the headlamp vacuum system with specific switches and two different style wiper door actuators. All 1968 and early 1969 wiper door actuators use a fiber piston seal that rides in the canister bore. Late 1969 wiper door actuators resemble a headlamp actuator with a captured rubber diaphragm in the center and an actuator shaft seal. The later wiper door actuator is very reliable, and if necessary, the actuator rod seal is replaceable. Due to their design, all early actuators have vacuum leakage by the fiber seal – some more, some less. For instance, you can close off the back side of the later actuator vacuum connection, preventing any actuator rod movement, while the early actuator will let you move the actuator rod as the vacuum bypasses the fiber seal. The wiper door control system is more complicated than the headlamp system due to wiper door and wiper mechanism movement. 1968-1971 Corvettes control the wiper door vacuum solenoid through a relay, which was dropped for the 1972 model year. The ’68-’71 wiper relay was placed in the console area and is controlled by the wiper switch. The 1969-1972 Corvettes use the same vacuum control solenoid as the 1968-1971 without the relay. The vacuum solenoid is a simple device that opens, allowing vacuum to dump when 12-volt power is applied. The solenoids are reliable – we see more damage from connector removal than solenoid failure. The connector must be carefully removed with side-to-side movement, or the terminal can be pulled out of the solenoid. 1969-1972 Corvettes use a vacuum switch on the wiper arm to prevent door closing until the wiper arm is fully parked. All of the wiper door systems use an override switch under the dash to bypass the relay (1968) and solenoid. The vacuum solenoid receives a signal from the wiper switch to route vacuum to the vacuum relay valve. Like the headlamp system, the relay valve sends vacuum to the wiper door actuator. All ’68-’72s have an additional override vacuum switch under the dash to open the wiper door.
Problem Areas: Like the headlights, vacuum leaks are the major concern, with a few switches that come into play. The 1969-72 wiper arm switch is prone to failure from the harsh environment (sunlight, water, etc.). All of the headlamp and wiper door vacuum systems use a vacuum reservoir to supply ample vacuum for quick wiper door operation. The same driver-side rear inner fender reservoir is used for the wiper door and headlamp system. The common problems are wiper arm vacuum switch, relay valves, and poor hose connections. The easiest way to troubleshoot the myriad of vacuum components is with a good vacuum gauge and pair of needle-nose pliers. Caps and plugs help isolate one system from the others, which in many cases, must be done because you may have multiple leaks. You can have all the relay valves leaking for both the headlamps and wiper door, for example. If you have access to a vacuum pump (an A/C vacuum pump works well), you can troubleshoot the system without the engine running to listen for audible leaks in the systems. If you are using the engine or an external vacuum source, you first need a baseline vacuum reading. This can be done by removing the vacuum source rubber hose and connecting the vacuum gauge to the engine if you are using engine vacuum. If you are using an external vacuum source, connect your gauge directly to the pump for the baseline reading. The next step is to tee the vacuum gauge into the vacuum system close to the source to begin leak checking. Then move outward on the vacuum source hose, clamping it with the needle-nose pliers until you see a rise in vacuum. If you are working with a ’68-’72 car, start by eliminating the headlamp vacuum system by plugging the supply line at the headlamp relay valve. If the vacuum reading rises, you know you have a leak at the front in the headlamp area. If the vacuum reading stays the same, plug off the wiper door vacuum supply hose and see if that makes the vacuum rise. You should be within an inch or two of the first vacuum reading when all the ports were blocked. What we need to know: Is the vacuum leak from a leaking relay valve or actuator? Since relay valves are prone to leaking, we can easily test them by plugging the green and red outlet ports. A good relay valve will have the vacuum rise close to the baseline vacuum. If it is down more than two to three inches of vacuum, the relay is bad. To save multiple part orders, you can use a vacuum splice connector to bypass the relay valve connecting the red vacuum actuator hose to the yellow supply hose to check for a vacuum loss. If you find a leak, the actuator diaphragm or the canister has a perforation. Actuator replacement is the only answer at this point. This same test can be done with the green actuator hose and the yellow supply hose. The green actuator hose is the push side that opens the headlamp or wiper door. Finding a leak on the green side of the actuator usually means the replaceable actuator rod seal is leaking. If there are no significant vacuum leaks and the headlamp doors do not work, you can apply vacuum to the relay valve’s small vacuum control port to see if the headlamps operate. You should find vacuum at the small hose when the headlamps are on. If no vacuum is found, look inside the car for the problem. If you found vacuum at the small hose, the relay valve is the problem. That is, of course, if the headlamp doors are not mechanically binding.
Do not be surprised if you find both of the systems leaking. Careful troubleshooting and repairs will get rid of the leaks, and you will even enjoy better engine performance. You will not be able to adjust the carburetor(s) to compensate for headlamp and/or wiper door vacuum for leaks that occur at the intake manifold. You can try to compensate for the vacuum leaks by adjusting the carburetor idle screws richer; but remember, the vacuum loss is after the carburetor so poor performance will result.
Inside Challenges: The cockpit vacuum system also has a myriad of hoses to contend with, but the difference is that they do not affect engine performance. Cockpit vacuum leaks are usually minor but significant because they operate at low volume, so any loss of vacuum can affect proper operation of the headlamps or wiper door. The headlamp control is simple; vacuum is supplied to the headlamp switch, and the headlamp switch routes vacuum to the headlamp door relay valve. The wiper door control is more involved and utilizes an electric vacuum dump solenoid that the wiper switch electrically controls. Both the headlamp and wiper door controls have an override switch to manually dump vacuum for wiper blade or headlamp replacement.
Cockpit vacuum problems usually occur after dash repairs have been performed because a vacuum hose is knocked off or broken. Original vacuum hoses usually fit loosely because of age, making them easy to knock off. The hoses themselves are not subjected to the under-hood heat so they stay in good condition for quite a while. Once all the hoses and components are installed, adjustments come next. Remember that the wiper arm vacuum switch must be fully depressed to allow the wiper door to close; likewise, the wiper motor armature switch must be depressed fully to allow the wiper motor to run.
Like our headlamp vacuum system, the wiper door vacuum system was in total disrepair, requiring us to replace all the vacuum system components including the relay valve, wiper arm switch, and all of the hoses. The vacuum hose kit system came with clear instructions on what length hose and indicates what color stripe goes where. Look at the supplied instructions and vacuum hose diagram carefully to assure that the correct length/color stripe hoses are used. It is easy to grab the wrong hose and think that something is wrong with the length. Take a tape measure and measure the hoses first – no cutting is required!
The Bottom Line: This is certainly a big step in driving the 1969 Corvette on long road trips. It is very nice to know that the headlamps operate without our under-the-car manual intervention. Having wipers that come on when you request them takes some apprehension away when we drive the ’69. One thing is certain – we will take the ’69 Roadster on longer road trips in 2010. Who knows? Maybe it is time the Corvette makes the trip to Corvettes at Carlisle.