1970 Headlight and Wiper Door Problem

[William H.]

I have a 1970 350/350 with AC and when the car is started, both the headlights and wiper door open all at the same time and then immediately close. Once they cycle through this, each component works as intended. Headlights work correctly when actuated and same for the wipers.

All components have been rebuilt and or replaced so I am not sure what is causing this problem. Does anyone have any ideas what could be wrong? Thanks!

[Geoff C.]

Re: 1970 Headlight and Wiper Door Problem

check valve

[William H.]

Re: 1970 Headlight and Wiper Door Problem

Has anyone had a similar vacuum issue? Thanks for any help.

[Leif A.]

Re: 1970 Headlight and Wiper Door Problem

I believe Geoff addressed your issue in post #2. And, yes, I had a similar issue on a '72 I owned...check valve.

[Edward J.]

Re: 1970 Headlight and Wiper Door Problem

William, I had a similar situation where the wiper door only would do the cycling up and back down, and it ended up that the vacuum switch under the wiper grill was the cause. the passenger wiper arm rests on the button of this switch when wipers are parked.

[Patrick H.]

Re: 1970 Headlight and Wiper Door Problem

I agree with Geoff and Ed.
Check valve, switch under the grille, or 3rd thing is vacuum leaks. If your vacuum leaks down while sitting, you may have an "unbalanced" vacuum system. This will then cause the movements you see until the engine makes enough vacuum to pull them back in place.

Geoff (aka Doc Rebuild) makes an excellent diagnostic pamphlet regarding the vacuum system. It would not surprise me at all if you have more than one problem. In trying to get a 72 to pass PV last year we had to go through a lot to make the system work as designed or better.

[William H.]

Re: 1970 Headlight and Wiper Door Problem

We have swapped 3 different check valves as well as the wiper door vacuum switch and still have the problem. It very preculiar that both the headlights and wiper door open at the same time when the car is started.

[William H.]

Re: 1970 Headlight and Wiper Door Problem

Thanks, Patrick. I am going to run with your idea. We have swapped everything out and it could be a leak probably in one of the hoses. Will get the Dr's pamphlet as well.

[Patrick H.]

Re: 1970 Headlight and Wiper Door Problem

The reproduction wiper door switches are junk. Even the ones that were "supposed" to be good are not good.

Last year in preparation for PV we found that the original on the car was broken. I told the owner to order two of the ones that were supposed to be better. We did - and one failed 10 days prior to PV. Thankfully we had the second one, swapped it out, and made it. Ironically, we were told shortly thereafter that they were no longer available. The commonly available ones have a failure rate nearing 90%, so I would not trust one of those. In addition, some of the reproduction check valves are just as bad.

After you get Geoff's pamphlet, test everything. Each piece should perform exactly as described.

FYI the diverter valves in the nose sending vacuum to each headlight as well as the wiper door are common leak sources.

[Terry M.]

Re: 1970 Headlight and Wiper Door Problem

We have swapped 3 different check valves as well as the wiper door vacuum switch and still have the problem. It very preculiar that both the headlights and wiper door open at the same time when the car is started.

The vacuum system on C3 Corvettes has two circuits. There is a control circuit (the smaller hoses) and the actuation circuit (the larger diameter hoses). Because of the smaller diameter hoses the control circuit has a lesser volume than the actuation circuit. The two systems are supposed to work together such that as the vacuum comes up because the control circuit has less volume it should build vacuum before the actuation circuit. Thus if there are no or few leaks the doors should stay in place as the vacuum in the system builds.

All that is fine until the control circuit develops a leak. If the leak is large enough the control circuit will not build vacuum before the actuation circuit and the result (depending on where and how large the leak is) is dancing headlamps wiper door or all three.

You have a leak in the control circuit and the best way to find it is to "T" a vacuum gauge at the port of the intake manifold where the filter to the vacuum system is. Use a pair of needle nose vise-grip pliers to begin blocking off parts of the control circuit. Don't forget the relay on the back of the tachometer and the over-ride switches under the steering column. As you block off each part of the control circuit you will see the vacuum needle rise momentarily when you find the leaking portion. It is easiest to do this if you have an independent source of vacuum == an AC system vacuum pump works well. This can be done using engine vacuum, but with the engine running you will never hear a leak and you will have to watch the gauge more closely.

[William H.]

Re: 1970 Headlight and Wiper Door Problem

Terry,

Great insight and explanation. Thanks very much for your help and direction.

Bill

[William H.]

Re: 1970 Headlight and Wiper Door Problem

Still have an issue and can't find a vacuum leak. When the car sits for a while and is started, both the headlights and wiper door open momentarily and then close. Once the car is running, both systems work well and open/close quickly. If the car is restarted shortly thereafter, the headlights and wiper door stay closed.

Thanks for any further counsel. Bill

[Patrick H.]

Re: 1970 Headlight and Wiper Door Problem

Did you go through Doc Rebuild's troubleshooting guide?

Did you check to see that the silver check valve is functioning correctly?

I suspect you have a leak, but it's a matter of finding it. They can be tricky.

[Mark E.]

Re: 1970 Headlight and Wiper Door Problem

Use a vacuum pump as you test the system and check for leaks. This allows you to charge the system with the engine off so you can hear leaks.

[Anthony F.]

Re: 1970 Headlight and Wiper Door Problem

I had a similar problem recently, but only related to the wiper door.

At the rear of the wiper door actuator, I pulled back the actuator boot and noticed the seal had somehow pulled out of the housing ( from the linkage rod going back and forth? ). I reset the seal and the problem was corrected.

I realize that this probably wouldn't help with the headlamp issue, but you might have multiple problems going on, and this only takes a minute to check and fix.