Topic: '72 Wiper Door Malfunction
in Forum: C3 Body
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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
?|UPDATED|6/6/2025 9:16:44 AM (AZT)|/UPDATED|
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Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
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...
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...
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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. 
Wow, Joel and Mike those were great replies
! 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?
! 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?
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
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.
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.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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 
!!!!!!!!!!
!!!!!!!!!!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
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
Glad Mike was able to take care of ya, Roger!
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Well I replaced the check valve and filter in the vacuum line off the intake manifold and it did not fix the problem
. 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
. 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.
. 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
. 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????
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
It's the relay leaking...
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
in Forum: C3 Body
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