C3 Wiper Door Opens at Start Up

[Tom Bishop]

My 69 wiper door opens immediately at start up. I have just replaced all the hoses with new ones & followed all the diagrams & documents very carefully. This is a complete frame up resto & I do not know if the wiper door acted this way prior to my owning the car. I have opened & closed all the appropriate switches in all different orders & it doesn't seem to matter which order or what position they are in, the door always opens on start up. Is there a component that might be faulty or a hose in the wrong spot? Befuddled.

[Patrick H.]

Re: C3 Wiper Door Opens at Start Up

Tom,

It most likely means a faulty component. In a nutshell, while the car is off you are slowly leaking the vacuum that was built up in the system. When you start the car, the wiper door bounces up until vacuum is built up in the system, "balances" itself on the wiper door actuator, and the door goes back down.

Make sure the 3 port valve connected to the back of the intake port (silver disc item) is new.

I often find that a headlamp actuator leak is the cause of the problem you are experiencing, but you'll have to go around and test.

Patrick

[Jon S.]

Re: C3 Wiper Door Opens at Start Up

This is a common ailment that many folks (myself included) have asked about. Patrick hit the high points, but you can also find some very detailed tests and checks if you search the archives.

[Jim T.]

Re: C3 Wiper Door Opens at Start Up

Tom and Patrick, My original owner 68 still has all original hoses,relays, and headlight vacuum motors. The vacuum motor for the windshild wiper door was replaced in 74 because the shaft broke. The vacuum line filter,metal check valve, and headlight switch have been replaced through the years of ownership.
After the 68's engine is shut off the vacuum will not stay in the storage tank very long, but even with no vacuum in the system, the 68's wiper door does not open when starting the car.
My original owner 70 is pretty much the same as the 68 in replaced components except the original vacuum motor for the windshield wiper door is original. The wiper door also does not open with no vacuum in the system on startup.

[Jon S.]

Re: C3 Wiper Door Opens at Start Up

I may be off base here, and I'm sure someone will correct me if I am.

The vacuum system is controlled by two almost completely separate circuits (they split at the check valve). The "control" circuit tells whether to open or close the doors based on the actuator position, and the "servo" circuit actually does the work of opening and closing the doors. The way I understand it, when you start the car, the two circuits begin to build vacuum - in essence 'racing' to build vacuum first. The whole system is biased to the control circuit, so that it will build vacuum first, the actuators will then get set appropriately based on switch positions, so that by the time the servo circuit builds vacuum, the doors stay where they should be.

I take that to mean that, even if all the vacuum bleeds off while the car is shut down, and maybe even if you have some leaks in your system, as long as the control circuit can 'vacuum up' before the servo circuit, the doors will not move.

[Jack H.]

Good!

Jon, hit the high points of my prior posts on this subject right on the money (see archieves)!!!!

There is a race condition that the servo path of the vac system is winning vs. the control path that was biased by design to 'win'.

The wiper door's vac T's off the RH headlight, so system leak(s) (don't expect there's only one to find/trap/kill) can exist at the HL causing the wiper door to 'dance'....

Getting one of the vac system troubleshooting phamplets (most Corvette catalog houses) and going through the vac system point by point is really the only way to trap and kill the individual leaks.

Hint: with the problem car's engine running, it's a bear to find leaks by ear.... What we do at the shop is SIMPLE. Take a second vehicle, park it outside the garage, run a LONG hose from it to the problem car and close the garage door. Use the second vehicle's engine vac as a source to power the problem car and quite frequently the problems become SO obvious (suble hissing) that you don't need to walk around with pressure gauge checking each hose connection/device in the system.

Last: don't assume the problem lies in the engine compartment! The vac control path splits at the check valve and enters the cockpit to run the various control switches in the dash (wiper door solenoid, HL switch, under instrument panel over ride switches). You could have leaks there too, especially if 'Buba' has pulled the speedo/tach cluster recently....

[Jim T.]

Re: C3 Wiper Door Opens at Start Up

On the subject wiper door there is a inexpensive repair to the seal of the wiper door vacuum motor I will repeat as learned from an article in Vette Vues several years ago.
A baby bottle nipple can be used to replace a bad seal of the vacuum motor that operates the wiper door. I purchased a package of two old style clear silicone type baby bottle nipples and installed one on my 70's windshield wiper vacuum motor about 13-15 years ago. The only change to the baby bottle nipple is a clean appropiate size round hole in the nipple end. It is still working. This seal is hidden from view by the dust cover over the shaft. Judges could pull back this dust cover and see the baby bottle if you are having your car judged. The correct seal is available from multiple Corvette catalog parts establishments.

[Jon S.]

Re: Good!

I learned it from you, Jack. :-)

Followup question: How about the rear Astro Ventilation door? Under the shift console the vacuum Ts off and heads back to the cannister for this door. I'm not sure if there is a control circuit for this, but is it possible that a leak in this end of the system could cause the wiper door to pop on startup?

[Jack H.]

UJ (Uncle Jack) is guilty....

of not mentioning the rear Astro Ventillation actuator control line, Jon! That's because his little corner of the universe is A/C equipped and this door was fixed/closed with a permanently plugged vac line.... Nice add-on, amigo!