Vacuum thingee on the firewall

Old September 10th, 2011, 09:31 PM
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Vacuum thingee on the firewall

Hello,
Can anyone tell me whats the purpose of the black circular part that bolts onto the firewall located right next to the voltage regulator. My car is a 72 Cutlass convertible and its on my 72 cutlass hardtop supreme as well. I think it's some sort of vacuum piece.
What does it do?
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Old September 10th, 2011, 09:42 PM
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Vacuum canister... for A/C I believe. I know my A/C did not work at one point, and it was b/c one of those small vacuum lines was broken on the inside under the dash.
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Old September 11th, 2011, 06:12 AM
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Yes, it stores vacuum to run the A/C vacuum doors and water valve. Without it, the dampers in the heater box will go bonkers when vacuum drops while engine is under high loads.
Inside it is just a diaphragm and spring.
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Old September 11th, 2011, 08:00 AM
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I don't think it's necessarily just for A/C cars. My non-A/C '67 Delta 88 has one. It's there to provide a vacuum reservoir regardless of engine speed, etc., and it's needed if anything is vacuum-operated in the heating or A/C system. Even with no A/C, the various vent doors are vacuum-operated.

Mine's circled in yellow below.


Last edited by jaunty75; September 11th, 2011 at 08:02 AM.
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Old September 11th, 2011, 08:17 AM
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My '68 4-4-2 doesn't have any of those vacuum cannisters on the firewall. They served a number of purposes, depending upon what options are on your car. The '68s that had a remote trunk release (vacuum operated at that time) had a cannister in that position on the firewall. If you had other options, such as A/C, power door locks, and cruise control, there could be as many as 3 of those cannisters mounted at other places under the hood. My car has none of those options; thus, no cannister -just the dimples in the firewall where it/they are supposed to go if the options were present.

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Old September 11th, 2011, 03:06 PM
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Originally Posted by jaunty75 View Post
Even with no A/C, the various vent doors are vacuum-operated.
Not true for Cutlii. The heater-only system is cable operated, no vacuum. I cannot speak for the full size cars. Of course, this vacuum canister is used for any vacuum actuated accessory such as power trunk or door locks. There isn't a lot of vacuum to pop the trunk when the engine's not running, thus the need for the reservoir. I'm pretty sure there is nothing inside the cannister, by the way. The later cars have an external check valve that is in line with the canister, but the older ones may have the valve built in.
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Old September 11th, 2011, 03:19 PM
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Originally Posted by joe_padavano View Post
Not true for Cutlii.
OK, fine. But it's obviously true for my car, which has no A/C but does have vacuum-operated vent doors.
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Old September 11th, 2011, 03:36 PM
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Originally Posted by jaunty75 View Post
OK, fine. But it's obviously true for my car, which has no A/C but does have vacuum-operated vent doors.
Yes, but from the O.P. (and to avoid confusion):

Originally Posted by projectheaven View Post
My car is a 72 Cutlass convertible...
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Old September 11th, 2011, 03:38 PM
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Originally Posted by joe_padavano View Post
Yes, but from the O.P. (and to avoid confusion):
True, but the question I was answering came from the comments following the OP. Vacuum-operated doors also were a feature of at least some non-A/C cars. I should have stuck to that.
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Old September 11th, 2011, 04:43 PM
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Originally Posted by jaunty75 View Post
True, but the question I was answering came from the comments following the OP. Vacuum-operated doors also were a feature of at least some non-A/C cars. I should have stuck to that.
Which is why I specified Cutlii in my first post. I guess the completely unambiguous way to phrase it might have been "Full size cars without A/C also used vacuum actuated doors." I know this is really beating a dead horse, but inexperienced people are sometimes easily confused by phraseology that is not completely unambiguous.
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Old September 11th, 2011, 05:52 PM
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and there is a spring, diaphragm, and check valve inside.
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Old February 13th, 2013, 09:05 AM
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Where can I get one of those ?
(mine is MIA)
Can't seem to locate it in any of the parts catalogues - maybe i am using the wrong terminology....
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Old February 13th, 2013, 09:16 AM
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I think this is going to be a junkyard part.
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Old February 13th, 2013, 04:56 PM
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Put a parts-wanted post out there - there are many good used ones still out there.
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Old February 13th, 2013, 05:11 PM
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I have a few laying around if you are interested in one. $25 plus shipping.

Brian
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Old May 1st, 2013, 08:49 PM
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Hate to gravedig, but...

My canister has had one of the vac lines cut too short (black w/ white stripe?), do I just buy a coupling and a bit of hose? Or does it need to have a tee for manifold vacuum?
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Old May 2nd, 2013, 05:10 AM
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Originally Posted by 69442C View Post
I have a few laying around if you are interested in one. $25 plus shipping.

Brian
Wow! I didnt know these things were worth anything? I removed the one from my car when i made it "heater delete" and just tossed it into the trash can!! LOL. I've probably done that with a lot of 'sellable" parts over the years! Ought to know by now that everything has a "price" -eh? LOL
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Old May 2nd, 2013, 10:01 AM
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Question

Originally Posted by KDV View Post
My canister has had one of the vac lines cut too short (black w/ white stripe?), do I just buy a coupling and a bit of hose? Or does it need to have a tee for manifold vacuum?
Kinda confusing on where they go.

The only diagrams I find in the manual (attached) refer to the 455 engine (I have a 350). And on everybody's lovely photo of their engine compartments that is always right behind the air filter (just out of view).
Attached Images
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vac-hoses-1-5-a.jpg (77.4 KB, 45 views)
File Type: jpg
vac-hoses-1-5.jpg (90.1 KB, 39 views)
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Old May 2nd, 2013, 01:15 PM
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Thank you! Thank you!! Thank you ddd777!!!

I've been looking everywhere for those... are those diagrams from the assembly manual?
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Old May 3rd, 2013, 07:16 AM
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Talking

Originally Posted by KDV View Post
Thank you! Thank you!! Thank you ddd777!!!

I've been looking everywhere for those... are those diagrams from the assembly manual?
yes. you can find them on wildaboutcars.com (a great resource).

let me know if you run across definitive info on what i should do with my 350 hoses...
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Old May 6th, 2013, 01:07 PM
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Hooked my hoses up just like the schematic. I didn't solve my problem - no air through the vents and no a/c - but I may have a problem somewhere else.
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