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Hi, 1972 LS5 PS,PB,AC 4spd. Both headlamp and wiper systems have worked for 10 years as they should until last week. Lights come on but doors do not open,wiper door doesn't open. Checked manifold pressure at check valve 15in. Gave check valve the blow test and it passed. Filter clean
Did the 15 sec. test that FM- Rescue Roger suggested and nothing happened. I can hear a clicking sound when I try to turn on wipers. Over ride switches do nothing. All vacuum lines appear to be good. What next? Thanks, Bob
After the check valve comes a filter with two ports. One port goes to the relay on the firewall and the other goes to the two manual switches under the dash and the headlight switch.
Do you have vacuum at both ports?
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If both systems failed simultaneously then it would be on a common line. The control vacuum line goes into the dash and has a T that splits the control vacuum source between the vacuum relay on the tach and the headlight switch. I would look in that area from J to A and all 3 hoses. The headlight switch, the T or the relay must have failed or the vacuum tank itself or the hose going to it is leaking on the control side. Or the tank to the actuator solenoids is leaking on the work side. The easiest thing to do is split the systems
I would vacuum test from the check valve out to those systems so you can determine which side to investigate.
1 unplug the check valve and hook up your vacuum tester to the rubber line going into the dash and see if it will hold a vacuum
2 if it does do the same test going into the vacuum tank. It will take a lot of pumping to draw it down http://repairs.willcoxcorvette.com/w...-schematic.jpg
Last edited by Rescue Rogers; Sep 30, 2019 at 07:16 PM.
OK I removed line going through dash ,could not pull vacuum. Next I checked line going to vacuum tank, could not pull vacuum. So I removed both lines to the actuators at the vacuum tank,plugged one and vacuum gauge to the other. Got 16in while engine running,when shut down vacuum decreased to 0 after a minute or so. Thanks,Bob
RR Pulled vacuum on both lines nothing happened until I turned on headlamp switch , then they both would open and close when switch turned off. Thanks, Bob
What direction am I going except crazy. OK at least I think I know the headlamp system is working Does that mean the headlamp switch is working right? If theadlamp system is working does that mean the problem is in the wiper system? Thanks
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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lets start over. If you unplug numbers 3,4 and 5 then put in a tee, you will bypass the vacuum tank when you start the car. if the issue is in the tank then everything should work fine with the car idling with good vacuum. Both the wiper cover and the headlights. You said you were able to get the lights working. So if you did this then the issue isnt on the control side , its on the working side. That elominates the switch and the actuators and hoses on that side.
I labeled the control side as 6, 7, and 8 where you could split the control side and test easht side by eliminating one control side at a time. if need be
Let us know where you disconnected the hoses so we can help you eliminate sections of the systems to narrow down the leaking part.
Last edited by Rescue Rogers; Oct 2, 2019 at 09:19 PM.
OK Ran full vacuum to both headlamps indivedually with headlamp switch on, both worked as they should. I hooked 3,4,and 5 in T. Right light and door opened fine, left opened and closed very slow. No action from wiper system. What do think? Thanks again
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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trace your hoses and make sure they are the same as the schematic. If it is, then 5 is the right light and door and 4 is the left light. Testing the lights individually and them opeing equally indicates that they propbably dont have alarge leak. It openning slowly in a group is indication it may be leaking, but it could just be a low vacuum signal just openning to much at once. Bypassing the tank and everything functioning would indicate a leak in the tank. If you can plug 2 of the ports and draw vacuum on the other see if yo can draw a vacuum. If you cant get it to hold vacuum, pull it and see if theres and visual holes or fill it with water and see if it leaks.
As for the wipers, once the door if fully open then they should function. THe door limit switch would connect the ground system to turn on the wipers. The switch is easy to test, just unplug it and when fully depressed it would just show short across the connectors. With the wiper door closed test it by pushing it in with your finger. With the door open you can test it again and see if the door is pushing in the plunger far enough to get the switch to close.
Last edited by Rescue Rogers; Oct 3, 2019 at 05:53 PM.
A couple questions Would a bad tank cause wiper system to fail? Why when I bypassed the tank the wiper system did nothing? I have to be out of town for the next week so I will put this on hold till I get back. Thanks again for your help.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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the electric wiper system itself is a seperate issue that may just be a coincedence. But if the door isnt openning far enough to trip the switch, then yes the vacuum system could be involved indirectly. But the tank itself would be a reason that would have a leak big enough that your wiper door and headlights werent openning originally.
Get back to us when you return, we should be able to get you back on the road. We'll get teh vacuum system working then work on the wipers
Last edited by Rescue Rogers; Oct 3, 2019 at 06:31 PM.
RR, Checked vacuum lines and all seem to be right according to the schematic. They all appear to be original but not sure. Pulled 10lb. with mighty mac on vacuum tank and has held for a couple hrs. Has not dropped at all. What next? Thanks
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Using the diagram disconnect the working side of the wiper system so that the tank vacuum will only be opening the headlamps and see if they open at the same rate. You will have to make sure you have adequate vacuum so either drive it around the block or let it run at a high idle for a few minutes. I'm trying to figure out where the issue is. I'm guessing theres a leak on the wiper side but I want to eliminate the headlights
Sorry if you've done this already but check the control and operation systems in whole.
Refer to that Willcox illustration provided by Rescue Rogers:
First remove the line indicated at (1). This is the supply for the control side of the system (both headlamps and wiper doors). Pump down with the Mitee Vac. It should pump down quite quickly and hold indefinitely.
Next remove the line indicated at (2). This is the supply for the operation side of the system (both headlamps and wiper doors). Pump down with the Mitee Vac. It will take quite a while as its volume is MANY times that of the control system. It should hold vacuum nicely but very unlikely anywhere near as long as the control side.
I suspect (but am not certain given what you've done so far) the you have a catastrophic leak in the control side.
Headlamp/wiper systems not working
