When I start up my '71, the wiper door opens 1/2 way, then closes all by itself. Searching through old posts, it seems like the recommendations were to replace the 1 way check valve. My check valve tested OK, but I ordered a new one----same issue. I put my old valve in a buddy's '70, and it worked fine--no issues with the wiper door.

Any other ideas or suggestions on what to check that would cause the door to open 1/2 way then close, only when starting? I do not notice it opening under full throttle (low vacuum) or when then letting off the accelerator (high vacuum). The other vacuum controlled systems (headlights and A/C) work fine..

THANKS!
Marc

 

The metal tubing that runs across the firewall is what sends vacuum to the wiper door relay to CLOSE the door. Remove the rubber hoses from each end of that tubing and blow compressed air thru it to clear any possible blockage. Retry. If it still does the same thing, the wiper door vacuum relay is likely the problem.

 

My understanding of this behavior is that the wiper door is to FAIL OPEN if you loose vacuum or have vacuum leaks.

So if your tank has bled down due to vacuum leak and you go to start it... The door will cycle open and closed at startup once the vacuum is restored.

NOW.. were is the leak.. I have a shutoff valve on my YELLOW stripped hose going over to the vacuum relay to stop this from happening when i start. Its annoying and my wiper door doesnt need the excercise. If i turn the vacuum off to the wiper door relay my vacuum tank will hold vacuum for days (i have changed things a bit and so my yellow hose provides vacuum to both the vacuum relay AND my bypass switch and tach solenoid I also dont have vacuum headlights anymore) so shutting this down turns all of those potential vacuum leaks off as well. I just replaced my wiper door vacuum relay as it was leaking down. I had to check my bypass switch , tach solenoid switch and hoses under the column to make sure they weren't leaking.

I am now down to my wiper door vacuum switch on the pass side wiper arm in the cowl leaking (these things are awful re-pops and leak when new at best). I found that after running i see my vacuum bleeding off slowly ... If i block the vent hose with my finger to the wiper door vacuum switch in the cowl (comes out by the distributor) and shut the engine off the vacuum leak stops. So now I need one of these gems.

May not be your issue but its worth investigating.

 

I would test the door actuator relay, they are the most common Failure. It tends to be the internal valve that has a minor leak by

 

The "winking wiper door" you describe is a very common issue with our cars with original components or even inferior newer ones. The reason the wiper door opens partially and then closes is because of an imbalance between the 2 vacuum circuits, the actuating side (large hoses) and the control side (small hoses). Any compromise in the components or hoses on the control side will allow atmosphere into it effectively raising the atmospheric pressure. This difference would negate the normal operation of the relay moving the internal switching piston to open until the vacuum builds up enough to override the vacuum leak.

There are several suspecting components that can do this, but by far the most common is the wiper arm safety valve residing under the passenger wiper arm. Testing it is a very simple procedure. If you have a vacuum pump like a Mightyvac, attach the pump hose to the middle port on the valve. Pump it up and it should hold vacuum. If it passes this test, depress the plunger and with the lower port blocked, pump it up. It should hold vacuum. Release the block on the lower port and the vacuum should disappear. If it fails either test, you have a new paperweight.

If you do not have a Mightyvac, there is another test you can do. First, disable the wiper arm movement by using the bypass between the 2 override valves to prevent the wipers from operating. Remove the middle and lower vacuum hoses to the valve and using a scrounged short tube of some sort connect the 2 hoses together. You now have effectively eliminated the valve from the circuit. Start the car and observe the result. If the door stays down, you have found the culprit.

If you need a new safety valve, do yourself a favor. DO NOT but another cheap piece of crap CHINESE valve. They are worthless! There is another valve on the market, made in the USA and sold by Willcox and a few others. I have attached a link........... Good Luck

https://willcoxcorvette.com/corvette...t-really-works

 

Have you got a picture of this metal tubing?

 

All c3 dont have the metal tube but shoptek should test his override switch

 

THANK YOU ALL!!!
I will check all pieces of advice---MUCH APPRECIATED!!!