A common C3 WS wiper door problem?

[Patrick B.]

My 70 LT-1 suddenly developed a problem with the ws wiper door vacuum system. The door works normally with either the ws wiper switch or the door override vacuum switch when the engine is running. However, about 10 seconds after the engine is turned off, the wiper door pops up. Is this a common condition experienced by other 68-72 owners? Did anyone discover the remedy?

[Rich G.]

Re: A common C3 WS wiper door problem?

My 68 does not do that. It must be a fault somewhere but I don't know the system well enough to troubleshoot. Also a buddy has two 68's and a 71 LT1 and they all work correctly.

Rich

[Alan S.]

Re: A common C3 WS wiper door problem?

Hi Patrick,
I think the first part I'd check is the check valve… it's the second of part of the vacuum systems in line at the intake manifold vacuum fitting.
It should hold vacuum at the side with the single nipple.
Regards,
Alan

[Patrick B.]

Re: A common C3 WS wiper door problem?

Allen ---- Is it the white thing or the grey thing?

[Alan S.]

Re: A common C3 WS wiper door problem?

Hi Patrick,
The first item is the white plastic filter, next is the gray metal check valve. It's purpose is to retain the vacuum in the system when the engine is shut off. They are known to leak and/or fail.
You should be able to suck through the two nipples but not at all through the single nipple. (A VERY technical test!)
Because the valve also splits the vacuum to both the 'control side' of the system and the 'servo side' of the system a leak can cause a variety of both headlight and wiper door symptoms.
Regards,
Alan

Look for Jack Humphrey's posts about 'winking headlights' and 'dancing wiper doors'. Good info there!

[Jim T.]

Re: A common C3 WS wiper door problem?

Alan you have a really nice clean engine and firewall.

[Alan S.]

Re: A common C3 WS wiper door problem?

Hi Jim,
Thanks very much.
Some folks find it a bit too pretty!
I tried to make it look like the workers at St.Louis were all having a really good day.
Regards,
Alan

[Patrick B.]

Re: A common C3 WS wiper door problem?

This is a follow up on the wiper door problem I described. I found the problem. The picture shows remnants of the vacuum safety valve that prevents the wiper door from closing until it is contacted by the right side wiper arm when the wiper arm returns to the retracted position. It is hidden below the louvered cast panel forward of the wiper arm pivot, and I had never noticed its existence before.

In this case, the plastic body of the valve broke from old age brittleness letting the spring pop the contact button off the valve (it disappeared somewhere in the cowl structure) and placing the valve in a condition where all three ports leaked to the atmosphere. When the car was running the vacuum leak was not great enough to prevent the other functions from operating, but after the engine was off, the broken valve would loose the control vacuum to the control valve before the vacuum tank lost all its vacuum to the operating part of the control valve, resulting in the wiper door poping open.

The GM part number of this valve is 5638487, but like most GM parts, it is no longer available. All the usual sources sell a Chinese repro for $25-$35 but they are complete junk. Dr Rebuild has a U-tube showing him opening the packages of 5 new repros and having them all fail to hold vacuum (and he sells them!). Happily, Willcox sells both the defective Chinese valves and a US made valve they claim actually works (for $55). The US valve is apparently made by a Corvette enthusiast that posts on Corvette Forum and sounds very knowledgeable in his comments about this problem. His valve is a different color and has slight variations in shape from the GM valve so Willcox warns that it might fail NCRS judging. But it is so hard to see that I do not care as long as it works. I haven't gotten the valve yet, but my hopes are high.

My car has only 40,000 miles on it and has been garaged 40 of its 45 years. The valve did not wear out; the plastic just broke from age when I tested the wipers in anticipation of driving it to an NCRS MAC chapter event (that was ironically cancelled in anticipation of rain). If this valve problem is not common on 69-72 C3's yet, it will be as age causes the valves to get brittle and break. 68's do not have this valve. I guess their wiper doors come down and snag the arms occasionally.

[Lawrence M.]

Re: A common C3 WS wiper door problem?

Patrick,
Thanks for the update. When you get the new valve let us know how it looks and how it works.

[Patrick B.]

Re: A common C3 WS wiper door problem?

Patrick,
Thanks for the update. When you get the new valve let us know how it looks and how it works.

Attached is a picture of the new valve beside the remains of the original valve. The bracket area of the US-made reproduction valve is different, however it operates very well and I am pleased with the quality. The degree of contact with the wiper arm required to actuate the valve (to allow the wiper door to close) differed by about 1/16" from the original valve and I had to adjust the attachment bracket on the car. The car bracket has sloted holes with clip nuts. I had to move both clip nuts 1/16" closer to the wiper arm, and then it worked fine.

The shiny new valve is visible thru the cast grill, so I guess those concerned with judging may have to search for NOS, pay $180 or so, and hope an old valve has not gotten brittle aging in the box.

[Tom L.]

Re: A common C3 WS wiper door problem?

I read your comment about moving the valve to adjust the moment of contact to close the door and it made me think. My door begins to close and ends up on the the arms as they park. Is this an adjustment that might correct that? I've played with the linkages with no success and kind of gave up. Thanks for any input!

[Jim T.]

Re: A common C3 WS wiper door problem?

This is a follow up on the wiper door problem I described. I found the problem. The picture shows remnants of the vacuum safety valve that prevents the wiper door from closing until it is contacted by the right side wiper arm when the wiper arm returns to the retracted position. It is hidden below the louvered cast panel forward of the wiper arm pivot, and I had never noticed its existence before.

In this case, the plastic body of the valve broke from old age brittleness letting the spring pop the contact button off the valve (it disappeared somewhere in the cowl structure) and placing the valve in a condition where all three ports leaked to the atmosphere. When the car was running the vacuum leak was not great enough to prevent the other functions from operating, but after the engine was off, the broken valve would loose the control vacuum to the control valve before the vacuum tank lost all its vacuum to the operating part of the control valve, resulting in the wiper door poping open.

The GM part number of this valve is 5638487, but like most GM parts, it is no longer available. All the usual sources sell a Chinese repro for $25-$35 but they are complete junk. Dr Rebuild has a U-tube showing him opening the packages of 5 new repros and having them all fail to hold vacuum (and he sells them!). Happily, Willcox sells both the defective Chinese valves and a US made valve they claim actually works (for $55). The US valve is apparently made by a Corvette enthusiast that posts on Corvette Forum and sounds very knowledgeable in his comments about this problem. His valve is a different color and has slight variations in shape from the GM valve so Willcox warns that it might fail NCRS judging. But it is so hard to see that I do not care as long as it works. I haven't gotten the valve yet, but my hopes are high.

My car has only 40,000 miles on it and has been garaged 40 of its 45 years. The valve did not wear out; the plastic just broke from age when I tested the wipers in anticipation of driving it to an NCRS MAC chapter event (that was ironically cancelled in anticipation of rain). If this valve problem is not common on 69-72 C3's yet, it will be as age causes the valves to get brittle and break. 68's do not have this valve. I guess their wiper doors come down and snag the arms occasionally.

Reference the 1968, my original owner 1968 convertible has never experienced the wiper door snagging the wiper arms, always closes after the wiper arms are parked. Wipers do not operate until wiper door is open. There is a electric switch activated by an arm that controls the operation/function. I bought a new valve from GM over 25 years ago for my 1970 and have not had install it yet.

[Patrick B.]

Re: A common C3 WS wiper door problem?

I read your comment about moving the valve to adjust the moment of contact to close the door and it made me think. My door begins to close and ends up on the the arms as they park. Is this an adjustment that might correct that? I've played with the linkages with no success and kind of gave up. Thanks for any input!

Tom: I'm assuming that your car is a 69-72 because a 68 does not have a vacuum safety switch. In order for the door to close, the vacuum valve on the firewall must get vacuum on the small control hose, in order to direct vacuum from the tank into the large hose going to the part of the actuator that closes the door. The vacuum safety switch blocks vacuum to the valve on the firewall unless the wiper arm pushes it, causing it to open the path for the vacuum. If it is misadjusted, the circuit does not know the wiper is parked, and the door will not close. Your problem is the opposite of a mis-adjusted vacuum safety switch.

I think your vacuum safety switch is bad (leaking vacuum). It should block vacuum until the wiper arm depresses its button.

To test my theory, pinch the small hose going to the vacuum valve on the firewall with the wipers operating and the engine running. Then, turn off the wipers while keeping the hose pinched. The wipers should park and the door should remain open. Next, release the hose and the door should close. If this happens, the vacuum safety switch is leaking, because the pinching and releasing of the hose is the same as the operation of a good vacuum safety switch.