Vacuum system troubleshooting
Thread Starter
Obsessed
Joined: Apr 2019
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From: Valencia, Spain
2025 C3 ('68-'73) of the Year Finalist - Unmodified
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Vacuum system troubleshooting
Hi Corvette Gurus, when I bought my 71 coupe the vacuum system worked great. I had a small issue with the whipper door opening when I started the motor but was able to figure out the problem, with a lot of help from the forum. The vacuum switch under the whipper arms went bad. Easy fix 😊. Everything else always worked great. Head lights popped up and went up and down quickly and together. Now the driver side light doesn’t open all the way and if I put on the whippers on while the lights are up the whipper door doesn’t open enough to let the whippers activate. If my head lights are not on, the whipper door opens fine and the whippers work. I’ve checked all the vacuum hoses and everything seems to be connected. I was hopping to find a disconnected hose. So my question is what’s the best way to go about finding what’s causing the problem. Are there some simple tests to eliminate a component or find where the problem is. Thanks for your help.
Le Mans Master
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From: mount holly NC
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Is my vette stock?? HAHA
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From: Im not allowed to tell you
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unplug a component one at a time and plug the hose. You'll find the culprit. Theres 2 systems, the "switch" system that tell the doors to open and the "power" system that does the actual work.
the switch side is the small diameter hoses and it sounds like that side is working. You can do as Derek says and trim off any loose or sloppy end stop make sure it isnt leaking.
The power side is the thicker hoses and the supply is usually yellow striped. So if you have a vacuum pump you should test the filter and one way valve at the beginning of your sustem and the hoses that go to the tank and the switches. Then where the T is on that system at he headlights I would disconnect the hose and plug it so its only working one side and test it to see if it opens fast or slow. Then test the other. Its always a leak whether its internal to a compnent or a hose. The relays fail the most, then the actuators are next on the list.
Ive replaced multiple wiper door actuator relays as the new onesdont last very long and replaced my headlight actuator fo rthe first time. I had the original 53 yearold relay in it still.....wish they still made quality ones in the USA
the switch side is the small diameter hoses and it sounds like that side is working. You can do as Derek says and trim off any loose or sloppy end stop make sure it isnt leaking.
The power side is the thicker hoses and the supply is usually yellow striped. So if you have a vacuum pump you should test the filter and one way valve at the beginning of your sustem and the hoses that go to the tank and the switches. Then where the T is on that system at he headlights I would disconnect the hose and plug it so its only working one side and test it to see if it opens fast or slow. Then test the other. Its always a leak whether its internal to a compnent or a hose. The relays fail the most, then the actuators are next on the list.
Ive replaced multiple wiper door actuator relays as the new onesdont last very long and replaced my headlight actuator fo rthe first time. I had the original 53 yearold relay in it still.....wish they still made quality ones in the USA
Thread Starter
Obsessed
Joined: Apr 2019
Posts: 627
Likes: 394
From: Valencia, Spain
2025 C3 ('68-'73) of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2019 C3 of Year Finalist (stock)
Thanks for the excellent info... I’m on it!! I’ll let you know how it goes...
Thread Starter
Obsessed
Joined: Apr 2019
Posts: 627
Likes: 394
From: Valencia, Spain
2025 C3 ('68-'73) of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2019 C3 of Year Finalist (stock)
Trimmed all the tubing but no luck... Divers side light still only opens a little. I have to pull it up the rest of the way open. They go down fine. Wiper door won’t open all the way with the headlights up but if the headlights are down it opens fine...🤷♂️
Team Owner
Joined: Jan 2006
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From: Crossville TN
You may have a vacuum issue. But you may also have a mechanical problem with the headlamp bucket hardware. Take a good look at how the mechanism SHOULD look, then check yours out. Or, since the left one is working OK, take a good look at it and then see if the right one looks and works exactly the same.
To eliminate the vacuum system as the problem, move or jumper the red-striped and green-striped hoses from the left headlamp vacuum relay and connect them to the right headlamp actuator. If the bucket still has the same issues, the problem is NOT a vacuum issue....it is either a mechanical issue or the right headlamp actuator can is defective. When the actuator functions, does it appear to have the correct amount of rod travel? If so, it's not an actuator can problem.
To eliminate the vacuum system as the problem, move or jumper the red-striped and green-striped hoses from the left headlamp vacuum relay and connect them to the right headlamp actuator. If the bucket still has the same issues, the problem is NOT a vacuum issue....it is either a mechanical issue or the right headlamp actuator can is defective. When the actuator functions, does it appear to have the correct amount of rod travel? If so, it's not an actuator can problem.
Last edited by 7T1vette; Jul 4, 2020 at 09:03 PM.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,209
Likes: 9,348
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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You still have a vacuum leak at the lights. go back to post #4
Last edited by Rescue Rogers; Jul 5, 2020 at 07:42 PM.
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