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Topic: '72 Wiper Door Malfunction

in Forum: C3 Body

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'72 Wiper Door Malfunction (1/15)
3/12/09 11:16pm

rdupler2
Former Member
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Hurst, TX - USA

Vette(s):
1972 Corvette Coupe. 350/200 Automatic with PS/PB/PW and A/C. Beautiful Bryar Blue. Unmolested original. Shooting for NCRS Top Flight someday.

Joined: 10/14/2007
Posts: 173

Had the '72 for a just about a year now and got caught in a unexpected shower Tuesday evening (first time I've gotten caught in the rain in it!) I had never used the wipers except when testing them prior to purchase. I had turned the wipers off about a block from home and the wiper door retracted and seated just as it should. Pulled it into the garage and turned off the engine and all seemed well. 3-4 minutes after I turned off the engine, the wiper door decided to raise up approx 1/2" and stay there. I started it back up and the wiper door closed again but every time I turn off the engine the same thing happens

Seems like if it was a leak then the door would raise up all the way after shutting down.

I'm sure this is not new to you veterans out there so someone can supply me a quick fix....right Thumbs%20Up

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'72 Wiper Door Malfunction (2/15)
3/13/09 5:10am

Adams' Apple

Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20189

Roger, the most likely culprit is the vacuum check valve.

This valve is in the vac. line that comes off of the back of the intake, just behind the carb. It is a metal, pie-pan shaped object, with one vac. line on one side, and two on the other. When this valve malfunctions, it can cause the wiper door to raise all the way up, or just a little when you turn the engine off.
The other thing that can cause this is the wiper door vacuum actuator relay valve, on the pass side fenderwell. Since you didn't have the problem before using the wipers that day, this may be your problem. The relay valve uses vac. to move a valve inside the relay, which routes the vacuum to either the "open" side or "close" side of the actuator outlets. If there is a leak inside the relay valve, it can let the valve move slightly when you turn the engine off, and allow vac. to the "open" side.

Somewhere here, there are a couple of threads on both of these items, and some testing info. If you want, I can e-mail you some vacuum checking info...

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Joel Adams
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'72 Wiper Door Malfunction (3/15)
3/13/09 8:23am

MikeMc71
Former Member
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Tucson, AZ - USA

Vette(s):
1970 White L-46 Air Roadster, 1971 White LT1 Coupe, 1971 Red Auto Air Coupe, 383 stroker, 430 HP, 2002 Millennium Yellow Auto Coupe

Joined: 10/7/2007
Posts: 341

This is the other valve to check. Its the wiper arw control valve. Its located on the passanger side, under the wiper door. The passanger side wiper contacts this in order to tell the system that its OK to close the door. If its leaking, or stuck so it won't fully open, it can also cause the door to open.

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'72 Wiper Door Malfunction (4/15)
3/13/09 8:44am

Wow, Joel and Mike those were great replies Smile

! I believe I found the line u r talking about Joel. It is the 1/2" vacuum line coming from the elbow fitting off the manifold behind the carb and going down to the white plastic fitting and then to the metal check valve?

Joel can you e-mail me the vacuum troubleshooting instructions you mentioned? Also does anyone have an electronic version of a vacuum system diagram?

'72 Wiper Door Malfunction (5/15)
3/13/09 9:24am

rraider1
Limited Member
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Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion

Joined: 10/14/2003
Posts: 1171

hope this helps

http://www.C3VR.com/member_pages/4201_4300/4221/Vacum-wiper-Headlight.jpg

'72 Wiper Door Malfunction (6/15)
3/13/09 10:15am

Adams' Apple

Roger...I e-mailed the info earlier today...."You've got Mail"...

If it didn't come thru, let me know, and I'll re-send it.

And yes, the metal check-valve is what I was referring to...it will cause the door to open a little, or all the way, depending on HOW it is malfunctioning. I say take a trip over to Phil's house, and do a little "parts swap"...

Just kiddin...but it would be an easy test to see if that is in fact the problem.

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'72 Wiper Door Malfunction (7/15)
3/13/09 11:01am

Robert, thanks for the link to the picture! That is great info. I appreciate that.

Joel, me thinks you have a good idea. Phil's at work today and I have the key to his garage Evil%20Smile

!!!!!!!!!!

I called and talked to "Mike" at Bairs. He was confident it was the check valve also. He's fixed me up with the check valve and a new filter for that line - a little over $20 bucks.

Thanks Joel very much for the pictures you sent. That is some great info also. My wife was in the e-mail before me this morning and she had clicked it and it didn't show up in BOLD print in the inbox anymore. That's why I overlooked it this morning.

Roger

'72 Wiper Door Malfunction (8/15)
3/13/09 7:52pm

Adams' Apple

Glad Mike was able to take care of ya, Roger!

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'72 Wiper Door Malfunction (9/15)
3/24/09 2:48pm

Well I replaced the check valve and filter in the vacuum line off the intake manifold and it did not fix the problem Unhappy

. Wiper door still raises back up about 3/8 inch 4 to 5 minutes after engine shutdown.

But this time, as I was bending over the right side of the car looking and wondering over the engine bay, I heard a sound like air rushing thru an orifice coming from under the right fender Shocked

. It was the Wiper Vacuum Relay. I started the engine, let the wiper door seat and shut the engine down. I hear the noise between the 4 and 5 minute mark every time just before the wiper door raises up.

Do you think it's a bad wiper vacuum relay or something between the relay and the bypass valve/solenoid valve arrangement under the dash that is the culprit????

'72 Wiper Door Malfunction (10/15)
3/24/09 6:19pm

Adams' Apple

It's the relay leaking...

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'72 Wiper Door Malfunction (11/15)
3/26/09 8:54pm

Joel, Thanks for the thought.

I was reading on another forum Shocked

that the small hose going to the actuator housing of that relay is the "control" line. Vacuum to that line causes the valve to operate and send vacuum to the front side of the wiper actuator on the firewall. If you lose vacuum on that relay actuator e.g., if that control line or a device in that control line leaks, then you will lose vacuum on the relay actuator and it will move in the other direction via spring force and thus cause the relay valve to send vacuum to the other side of the wiper actuator thus opening the wipre door Wacko

Oh well Phil and I will check it out asome more this weekend and will let you know what we find. Might be able to "borrow" the relay from Phil's car and test since his being a '69 it is very easy to get to.

'72 Wiper Door Malfunction (12/15)
3/27/09 5:05am

Adams' Apple

That's exactly how it works...spring and all! The valve has a "at rest" position. This position is supposed to leave the wiper door in the open position if there is a problem with the vac. system...sort of a "fail-safe" deal.

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'72 Wiper Door Malfunction (13/15)
3/27/09 8:44am

F4Gary
Standard Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air. 2017 Black Rose Grand Sport convertible.

Joined: 8/26/2006
Posts: 1491

If you do replace the relay, don't forget to recheck the timing on the engine since you just plugged a vacuum leak. I replaced mine just before we went on a Corvette Club cruise to Jefferson. It pinged all the way over and back. I couldn't figure it out until it just hit me. Duh.

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Re: '72 Wiper Door Malfunction (14/15)
3/25/25 7:40am

Martonea
Limited Member
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Winter Haven, FL - USA

Vette(s):
1972 454 Classic White Convertiy

Joined: 5/30/2024
Posts: 1

OK, I’ve read this thread and I’m still stuck wiper door open wipers come on for the windshield wiper switch. However, my manual override will not open the door. Any thoughts? I can’t find a vacuum leak anywhere.

Re: '72 Wiper Door Malfunction (15/15)
3/25/25 10:46am

F4Gary
Standard Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air. 2017 Black Rose Grand Sport convertible.

Joined: 8/26/2006
Posts: 1491

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