'72 Wiper Door Malfunction

[Terry M.]

Re: '72 Wiper Door Malfunction

Yes, the control circuit consists of small diameter hoses.

The C3 vacuum system consists of two circuits -- the control circuit is the small diameter hoses and this system provides the signal to the relay valves (or actuating valves) that determines what operates.

The power system provides the muscle and is the larger diameter hoses. They provide the large volume of vacuum (no that really sounds like an oxymoron) to actually move the part of the car (headlamp housings or wiper door).

BTW: Jack Humphrey has provided (time and time again) an outstanding tutorial on the C3 vacuum system for participants on this board. I know the search function on this board is not real user friendly, but if you can find one of his posts it will be worth your time. He is far more eloquent than I.

[Jack H.]

Re: '72 Wiper Door Malfunction

Bull, Terry! You 'done' an EXCELLENT job repeating what I would have said.

I generally give the tutorial to teach noice owners NOT to just blindly swap parts, BUT to understand the system (the books catalog houses sell DO that job), so they can troubleshoot in a knowledgable fashion...

There's something 'rotten in Denmark' here with the preceeding comment to the effect he could hear a rush of air from the wiper door relay in the RH wheel well. I suspect either the symptom analyis is wrong or there's a cockpit problem at the relay. Why do I say this?

Well, the relay simply directs the vacuum path of the servo side (what you called the power side). It switches servo vacuum to either open or close the wiper door. It does NOT vent vacuum!

The only venting of vacuum for the wiper door circuit happens at the door switch (lives in the cowl where the RH wiper arm presses against the switch during wiper park operation to let the system know the wipers have sucessfully turned off and it's OK to close the wiper door now).

The vent line from that switch DOES route back through the firewall into the engine compartment though... A 'stub' end of the vent hose protrudes a few inches through the firewall grommet where it 'hangs' in the breeze. That's done just to keep the open vent end from being able to suck air borne moisture (this IS a windshield wiper circuit and typical actuation occurs when there's water in the air!).

So, there shouldn't be any 'hissing' from the RH wheel wheel vac relay. It's control line simply tells it which way vac should be applied to the wiper door actuator (open or closed direction).

Now, that' presuming the relay isn't damaged...

[Terry M.]

Re: '72 Wiper Door Malfunction

You are far too modest Jack.

Not withstanding your modesty, as you know, I spend some time at the college trying to teach adults (trying to teach old dogs new tricks, and some of those dogs are older than I am) to trouble shoot their automotive issues and NOT just replace parts. I try to do that here and on some other boards too.

To try to trouble shoot problems over the Internet without benefit of hands, eyes and ears on the vehicle is a tall task. Certainly we can share the benefit of our "been there, done that and got the T-shirt" experience -- but that will never make up for eyes, ears and hands on the actual vehicle. All that said -- now for another suggestion:

Perhaps the old rubber hose to the ear trick will more accurately pin point the source of the "rushing air" sound. It could be coming from that vent hose, or the switch at the base of the wiper, and be mistaken for the actuating relay. The time delay before the sound occurs makes me think the control circuit has to bleed down before the sound occurs. See if you can identify the location of the rushing air sound.

Only rarely is there only one vacuum leak. A vacuum gauge Ted into the system and a pair of locking needle nose pliers to pinch off various parts of the vacuum circuits will isolate the other leaks that may not be audible. A thorough test, find and fix can lead to superior function.

I had (he has passed) a friend who got his 1971 (with AC) to hold vacuum over night and actuate the headlamps the next day. He went to some extraordinary lengths to achieve that, but it can be done.

[Roberto L.]

Re: '72 Wiper Door Malfunction

The following link could be of some help to understand the system. Sorry it is in spanish, but anyway you may understand the drawings.

http://www.geocities.com/bobluis/vacio.htm

I lost the translation (Jack do you still have it?)

Best regards

[Roger D.]

Re: '72 Wiper Door Malfunction

Well the sound is definitely coming from under the right fender from this device



Eckler's calls it a "Corvette Headlight & Wiper Door Vacuum Actuator Relay, 1968-1982".

Robert, Lo siento, Yo no intiendo Espanol mui bueno, por favor en Englase!!!

[Edward J.]

Re: '72 Wiper Door Malfunction

Roger,
The Wiper Relay Does Have A Vent On The Bottom, Keep In Mind If Its Leaking, Its Because Of Loss Of Vaccum, Tery Has A Good Idea Unbolt And Bring It Out To Listen Were The Vaccum Noise Is Coming From. Maybe Even Try Blocking Of The Vaccum Feed Hose While Engine Running Then Shut Car Of To See If The Door Stays Shut.

[Roger D.]

Re: '72 Wiper Door Malfunction

Thanks Edward/Terry. I'll give that a shot. My brother has a '69 and his wiper vacuum relay valve is mounted on the firewall. Maybe I can talk him into swapping into my car long enough to test it...but as old and delicate as these cars are sometimes then it might break his...hmmm maybe not. I'll find the problem I'm sure.

Has anyone tried any of the vacuum troubleshooting guide that the various parts places online have available? Are they any good?