Trouble-shooting 72 Wiper Door

[Steve]

Can anyone tell me how to trouble-shoot a wiper door that stays open? It initially would close when the engine was started then it finally stayed open permanently. Someone suggested earlier to replace the relay valve up under the front fender. I did and it closed when I started the car once and then has stayed open since. Anyway to trouble-shoot this problem would be appreciated. It is an LT-1 if that matters. Thanks Steve

[Jack H.]

Re: Trouble-shooting 72 Wiper Door

There's a troubleshooting book available from Corvette Centeral and Mid-America Productions that covers the Shark vacuum system (headlights and wiper door). It's helpful as a primer since there are electro mechanical systems and you can have system interaction (headlamp problems causing wiper door funnies and vice versa) as well as multiple faults on a single system.

So, without being a 'blow by blow' consultant/mechanic, I suggest you get the book, read up and see how far you get. Then, you'll be more knowledgeable to address point by point what's going on and what you've done to fix.

Last, lots of this is pretty simple and cheap (replace hoses, valves, make adjustments) and the book can save you big $ versus shot gunning the system with replacement components.

[Terry M.]

Re: Trouble-shooting 72 Wiper Door

Steve,

I am winging this because I don't have my reference materials here at work, but I believe your problem is a vacuum leak between that relay valve and the windshield wiper door solenoid mounted behind the tachometer. You need to get a vacuum gauge and "T" it into the vacuum signal to that relay. The small hose going to it is loosing vacuum and that makes the door open.

John Woods has chapter and verse on this and I need to brush up on it. I"ll e-mail John off the board and get him to respond to you.

Terry

[John Woods]

Re: Trouble-shooting 72 Wiper Door

Steve:

I think I can help you trouble shoot your wiper door problem. I'll start from scratch.

The wiper door is opened and closed by the presence of vacuum on one side or the other of the Wiper Door Vacuum Actuator. The integrity of the actuator can be tested by directly connecting a vacuum source to first one side, and then the other side to open and close the door respectively. If that works ok, you don't need to worry about the mechanics of the door or the actuator.

The vacuum is switched from the close (red hose) port on the front of the actuator to the open (green hose) that connects to the rear of the actuator. This switching of vacuum between the two hoses takes place at the vacuum relay valve that controls the wiper door. You indicated that it is located under the fender on your car, so you must have a '71 or '72 LT1. There are red, green and white paint marks on the vacuum relay valve that match the color stripes on the 3 big hoses that connect to it. Make sure they are not switched.

The vacuum relay valve can be easily tested, along with the performance of the vacuum actuator and door mechanics by using a small hand vacuum pump that can be purchased at any auto parts store. First, verify that there is strong vacuum on the white hose that connects to the vacuum relay valve. Do this by running the motor and testing with your finger. If there is plenty of vacuum there, plug it back into the port that is marked with white paint on the relay valve. The relay valve responds to the presence or absence of vacuum on the small control hose that connects to the valve. About 5 inches of vacuum applied to the control port on the relay valve causes the valve to switch vacuum from the open (green) hose to the close (red) hose. You can simulate this vacuum by attaching the hand held vacuum pump to the control port on the relay control valve and pump up vacuum. That should cause the vacuum relay to switch the engine vacuum source from the green to the red hose and close the door. If it does not work that way, your problem is not in the control circuit (small vacuum supply line) but in the power circuit which includes the relay valve, the power hoses, the actuator and the associated mechanics of the door.

To test the control circuit, you need something that will measure vacuum. Many of the hand held pumps I mentioned will do this or you can use a standard vacuum gage. Attach the gage to the small black hose that is connected to the wiper vacuum relay control valve. With the engine running, vacuum should be present when the door should be closed and there should be no vacuum when the door should be open. You can test this by simply switching the wiper on and off with the engine running. You should see the vacuum switch on and off on the gage. If this does not happen you have a problem in the control circuit. I didn't start there because you said that the situation has changed since you changed your control valve. However, the original problem might have been in the control circuit and still be there.

The vacuum control circuit for the wiper runs from the relay control valve, through the wiper door park vacuum switch (underneath the RH wiper arm), through the wiper door override switch (located under the steering column), through the wiper control soloniod (located behind the tach), where it joins to the wiper control circuit that performs the same function. Since you didn't mention any problems with headlamps, I assume that if you have a control circuit problem, it's somewhere between these components. Make sure that you didn't leave the wiper door override switch pulled down when you were working on the problem.

This all may be good cause for headache, but believe me, these systems are highly reliable and they work GREAT. We just need to know what the purpose of each device and how to isolate the problems. By testing in the manner that I have described, you should be able to determine exactly where the problems are (you might have more than one) and resolve them.

I didn't go into the detailed operation of the control circuit because I need to run right now. However, if you find that the vacuum is not switching on and off or if you need any other help on this, e-mail me back and I'll help you work through it. OK?