C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

How much vacuum to raise headlights?

Old 04-23-2019, 10:48 AM
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Default How much vacuum to raise headlights?

I've got a problem in the vacuum lines so I bought a HF vacuum pump to check it out. Would like to know specs or where to find on how much inches of Mercury it's suppose to take to raise headlamps and/or wiper door? Thx
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Old 04-24-2019, 04:23 AM
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Car is a 69? New actuators? any new parts? Leak in tank? a lot more questions before you start. What exactly is not working.
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Old 04-24-2019, 09:39 AM
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1" is enough to operate them, just slowly. I've tested with a hand-pump and be aware you need to pump a lot for something to happen.
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Old 04-24-2019, 09:54 AM
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i thought you weren't supposed to test the system with an electric vacuum pump?
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Old 04-24-2019, 10:35 AM
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I pumped the hell out of it at the main hose to lights by brake master and nothing held so must be a leak. I will attack each component separately. I suspect one of the lights diaphragms must be shot.
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Old 04-24-2019, 12:53 PM
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zwede is right, it doesn't take much but they go very slowly. Dad's car had a leak and while we were diagnosing and connecting up various parts looking for a leak we were disconnecting the tank so it had no vacuum. With no vacuum in the tank, a light would move as soon as the vacuum hose was connected at the same time vacuum was starting to build in the tank.

We found a small rust hole in the bottom of one of the actuators. A little JB Weld and it's worked fine since.

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Old 04-25-2019, 04:56 AM
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Most likely cause is worn-out vacuum relays (rather than the actuator cans). To test, just disconnect the vacuum feed on the relay and hook it to one of the actuator fittings so see if it works much faster (move hose to other fitting to close the housing). If it works well, replace the relays. If it works the same, replace the actuator[s] as needed.
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