projectheaven

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?

oldzy

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.

Lady72nRob71

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.

jaunty75

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.

rcorrigan5

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.

Randy C.

joe_padavano

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.

jaunty75

OK, fine. But it's obviously true for my car, which has no A/C but does have vacuum-operated vent doors.

joe_padavano

Yes, but from the O.P. (and to avoid confusion):

jaunty75

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.

joe_padavano

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.

Lady72nRob71

and there is a spring, diaphragm, and check valve inside.

ddd777

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....

jaunty75

I think this is going to be a junkyard part.

Lady72nRob71

Put a parts-wanted post out there - there are many good used ones still out there.

69442C

I have a few laying around if you are interested in one. $25 plus shipping.

Brian

KDV

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?

Chesrown 67 OAI

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

ddd777

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).

KDV

Thank you! Thank you!! Thank you ddd777!!!

I've been looking everywhere for those... are those diagrams from the assembly manual?

ddd777

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...

KDV

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.