Vacuum Help
Thread Starter
Racer
Joined: May 2004
Posts: 419
Likes: 4
From: MA
Vacuum Help
Lost my shop manual and trying to solve what I think may be a vacuum problem on my '69 BB (no A/C) car. Getting a hissing sound coming from the dash (maybe near the defog vents) when the thumbwheel is in the "off" position. If I spin the thumbwheel down to just beyond the "Air" setting it stops. Wondering if anyone can point me in the right direction.
Team Owner
Joined: Sep 2006
Posts: 31,173
Likes: 4,250
From: Westminster Maryland
Hi c,
First, you need to promise to order a new GM 69 Chassis Service Manual TODAY.
The wheels on the heater/defroster control operate the air doors in the heater/defroster box by vacuum.
Here's a picture.
Good Luck!
Regards,
Alan
Notice the vacuum 'pot', the hose isn't hooked to the nipple.
Both pots in this picture.
First, you need to promise to order a new GM 69 Chassis Service Manual TODAY.
The wheels on the heater/defroster control operate the air doors in the heater/defroster box by vacuum.
Here's a picture.
Good Luck!
Regards,
Alan
Notice the vacuum 'pot', the hose isn't hooked to the nipple.
Both pots in this picture.
Safety Car
Joined: Sep 2011
Posts: 4,104
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From: Madeira Beach, FL
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Maybe you have a cat or squirrel stuck in your vents and when you rotate the wheel the door pinches his tail???
Sorry moment of temporary insanity.
BTW, Alan has the greatest library of c-3 pics.
Now from a '68 BB owner, I think your on the right track.
See if with a powerful lite you can see the culprit.
I think with the wheel roatated to where the hiss sound is start pinching lines till it stops. Then you know which line is leaking.
It's probably cracked or split close to its mounting point.
Maybe you'll catch a break and be able to cut off the end not to far back and reattach.
Running a new line under there will be a PIA.
Marshal
Sorry moment of temporary insanity.
BTW, Alan has the greatest library of c-3 pics.
Now from a '68 BB owner, I think your on the right track.
See if with a powerful lite you can see the culprit.
I think with the wheel roatated to where the hiss sound is start pinching lines till it stops. Then you know which line is leaking.
It's probably cracked or split close to its mounting point.
Maybe you'll catch a break and be able to cut off the end not to far back and reattach.
Running a new line under there will be a PIA.
Marshal
Team Owner
Joined: Jun 2000
Posts: 38,923
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From: Southbound
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Thread Starter
Racer
Joined: May 2004
Posts: 419
Likes: 4
From: MA
Since I'm not going to be using the heater or defroster til the Fall, and also since I'm not prepared to do all the "while I'm at its" with the console/dash off, what would happen if I were to find the point at which the vacuum line to the dash enters at fire wall and clamp it off temporarily? Am I looking for just one line? According to the Wicox diagram there appears to be a single vacuum supply line running into the cabin. And would this cause any downstream effect on engine performance or on any any of the other vacuum-operated devices?
Last edited by cicconjo; Apr 26, 2012 at 08:50 PM.
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,481
From: Southbound
Cruise-In II Veteran
Team Owner
Joined: Sep 2006
Posts: 31,173
Likes: 4,250
From: Westminster Maryland
Hi cic,
I believe you can block off at the tee that supplies the vacuum to the heater/defroster control with out causing other problems.
Here's the location on my 71, near right side hood latch; not sure just where it is on your 69.
Regards,
Alan
I believe you can block off at the tee that supplies the vacuum to the heater/defroster control with out causing other problems.
Here's the location on my 71, near right side hood latch; not sure just where it is on your 69.
Regards,
Alan
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Thread Starter
Racer
Joined: May 2004
Posts: 419
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From: MA
-Joe
Thread Starter
Racer
Joined: May 2004
Posts: 419
Likes: 4
From: MA
Alan this was exactly the right line, thanks you saved me a lot of experimenting. Any idea what I can plug the T with so that it's not sucking in air? Guess I can just find a non-T adapter for now.
Last edited by cicconjo; May 5, 2012 at 02:05 PM.
Safety Car
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Napa or Lowes has very small vac line caps to block off unused line orifices. Plug the third part of the tee and your done.
Or like we did in the 70's just cut it off leaving about 3" and take a screw dip it in silicon caulk and run it into the hose end.
This way you can replace the hose at a later time. During non corvette weather
Tech tip: Take new length of hose and join it to old hose with a barbed nipple.
Pull the old hose through fire wall from inside the car and it threads the new hose through the grommet and to the desired location.
Like pulling house wire
Glad you found it.
Again, ever need a photo Alan probably has it.
Alan, I like all the toe tags in the interior photo.
Marshal
Or like we did in the 70's just cut it off leaving about 3" and take a screw dip it in silicon caulk and run it into the hose end.
This way you can replace the hose at a later time. During non corvette weather
Tech tip: Take new length of hose and join it to old hose with a barbed nipple.
Pull the old hose through fire wall from inside the car and it threads the new hose through the grommet and to the desired location.
Like pulling house wire
Glad you found it.
Again, ever need a photo Alan probably has it.
Alan, I like all the toe tags in the interior photo.
Marshal
