C-3 79 Vaccuum system

[Jeff Howe]

I am having trouble locating a major vacuum leak in the system. Not on the engine side but in the storage side. Is there any tool out there that can be purchased or made in my garage that will duplicate vacuum and what is a good way to find the leak? I have tried several ways. Thanks, Jeff

[Michael W.]

Re: C-3 79 Vaccuum system

If you have a wine and beer making shop near you, they most likely rent small electrically powered vacuum pumps normally used in conjuction with a filtering apparatus.

Attach the pump to the vacuum hose coming off the intake manifold and away you go.

BTW- don't stop looking when you find the first leak, most systems have at least two or three small ones.

[Harmon C.]

Re: C-3 79 Vaccuum system

A long hose from a car that is running outside your shop so you can hear the leaks will work. The clear plastic hose from any hardware about 30-50 feet long works well. An a/c vacumn pump and a portable air storage tank is what I use. In line shut off valves after the tank on the Corvette has about 20#s vacumn tells how fast it is leaking down so you know when the leaks are fixed. If the systems holds 15#s for 5 minutes it is fixed good enough for me.

Lyle

[Tom R.]

Re: C-3 79 Vaccuum system

I've always used a manual vacuum pump but it does have draw backs. I like what Mike and Lyle are describing here because you really need a constant vacuum to track down those leaks.

My question to Lyle is how do you hook up (connect) the running vehicle vacuum hose with the a/c vacuum pump and portable storage tank...or are the later two an alternative to the running vehicle? You mention the "inline shutoff valves after the tank" are you saying you insert inline shutoff valves or what? I understand the 20# vacuum...my 78 usually runs about 18 but by the time I get to the headlamp relays...I'm down to about 15#.

[Jeff Howe]

Re: C-3 79 Vaccuum system

Thanks all you guys for the response. The suggestion about hooking up another vehicle seems so obvious, but its not. Its pure genious. Thanks, Jeff

[Jack H.]

Using a 'dummy' vehicle...

parked outside the garage to supply vac to the car under test is the method we've used for years at our shop. It gives you a bone quiet environment to work with whereas an aux vac pump inside the shop is a pretty noisy critter (might as well just run the target vehicle's engine).

Simply park the donor vehicle outside, connect a LONG vac hose to it, route the hose into the garage/shop, close the door and connect the external vehicle to the Corvette using a coupling nipple to replace the source on the intake manifold. Now, follow conventional vac diagnostic proceedures walking from the source of vac outward along the car's vac system monitoring each connection.

You're looking for a drop of 2 PSI or more across an individual component and you need to selectively 'blind' parallel paths (plug one side and test the opposite side), to thwart mis-diagnosis. When you DO find a leak, do NOT presume that's the only one! Keep on going and verify the WHOLE system. It's not unsusual to have more than one leak point!

Last, don't forget to evaluate the car's in-line vac filter. These were supposed to be replaced periodically and many prior owners simply NEVER did maintenance due diligence here! A plugged vac filter can contribute all kinds of problem symptoms because air can't move fast enough through the system to stabilize (winking headlights, dancing wiper door).

Pull the in-line filter and hold it up to the light sighting through the nipples. You ought to see clean white gauze. If she's black as a coal bin OR you can see right on through, it's time for a fresh, new filter element!

[Terry M.]

[Kent K.]

Vacuum filter material availability?

Jack,
Is the filter material available through GM and/or many chain automotive parts stores? Any special item to request when explaining it to the store representative?
Thanks,
Kent #6201

[Michael W.]

Re: Vacuum filter material availability?

The filters are non-repairable throwaways, but replacements are available at any of the usual parts suppliers.

[Lyle24961]

Re: C-3 79 Vaccuum system

Tom
The system I use is a portable air tank beging used for vacuum storage. I pump the tank to 20#s on a vacuum gage on the tank and shut off the pump. I fill the system I am checking and shut the valve to the tank and see how fast the vacuum drops and listen for leaks.

Lyle

[Tom R.]

Re: C-3 79 Vaccuum system

So you're using it to test the vacuum storage tank on the troublesome vehicle?

[Jeff Howe]

Re: C-3 79 Vaccuum system

Yes, but checking entire system at the same time. I suspect the tank because reserve lasts less than a half a minute. Thanks Tom, Jeff

[Lyle24961]

Re: C-3 79 Vaccuum system

Tom
No I am testing the whole system but if the tank on the Corvette is full and dosen't last you have a bad leak and I have allways been able to hear the leaks and start fixing them. Are you at Auburn as I am look me up.
Lyle

[Lyle24961]

Re: C-3 79 Vaccuum system

The leak could be in lots of places and last less than half a minute. I have seen the headlight pods and relays to be the problem most of the time.

Lyle