Author Topic: Checking the (gulp) vacuum system on a 1967 Eldorado?  (Read 177 times)

Online 67_Eldo

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  • Name: sdownie
Checking the (gulp) vacuum system on a 1967 Eldorado?
« on: June 16, 2017, 05:50:16 PM »
As a byproduct of checking the wiring on my 67 Eldorado, I've discovered that a couple of vacuum hoses under the dash are disconnected. I couldn't see what they were once connected to. That's not a good feeling.

No matter how you approach it, the vacuum system has to be a mess to inspect. My car has the infamous Automatic Climate Control as well, but at least I don't have power door locks! :-)

Has anyone devised an optimal procedure for checking the health of the entire under-dash vacuum system or is it simply a matter of brute force disassembling the entire dashboard?


Offline Scot Minesinger

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Re: Checking the (gulp) vacuum system on a 1967 Eldorado?
« Reply #1 on: June 17, 2017, 12:05:59 AM »
The vacuum system is critical to a good running engine and accessory operation.  The climate control is great, enjoy it.

The only way to fix it is to go through each component and test it with a hand vacuum pump (sold at any auto parts store as a break bleeder), making sure the diaphragm holds vacuum.  I would replace all vacuum hoses under hood and snip off a 1/4" of all vacuum lines under dash and reconnect.  The climate control has a vacuum hose harness and you can't do too much with that.  Any vacuum line that penetrates the fire wall should be replaced. 

Replace vacuum lines one at a time!  The shop manual (would need Fisher body manual for power locks) should show how each was routed.  Since you do not have power locks, that leaves only cruise release, trunk release e-brake release and climate control under dash systems, go thru each - take your time.  Under hood replace each vacuum line one at a time.

After all vacuum lines are replaced the timing and idle should be checked an likely reset.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Online 67_Eldo

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  • Name: sdownie
Re: Checking the (gulp) vacuum system on a 1967 Eldorado?
« Reply #2 on: June 17, 2017, 09:18:22 AM »

I guess I'll pull the instrument cluster and start checking connections. It is hard for me to get under the dash, so I'll try to do as much as possible from above.

As it is, there is no cold from the a/c and the fan only seems to run at the lowest setting. But it is sort of entertaining to turn on the system and hear some vent door inside the dash slowly creak into position. It's Addams Family Climate Control!

I'm tempted to substitute a potentiometer for the climate-control thermistor because a) the dash pad containing the thermistor is out of the car, and b) because that might prompt the system to boost the fan speed (if the fan speed can be boosted). I need to determine the range of resistance that the thermistor supplies and then substitute the appropriate manually adjustable resistance.

Offline "Cadillac Kid" Greg Surfas 15364

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Re: Checking the (gulp) vacuum system on a 1967 Eldorado?
« Reply #3 on: June 17, 2017, 07:21:05 PM »
You know, there have been enumerable posts regarding vacuum systems , their hoses, their connections, leaks and the NECESSITY of replacing all the hoses immediately.  It has been my experience over more years than I care to remember that unless the vehicle has been abused by hammer mechanics or fires MOST of the vacuum lines, especially those inside the cabin can and do last for the life of the car.  By that I mean 60+ years.
The hoses can and do become unconnected when physical contact by someone working in their area causes them to move, and those under the hood can become hardened at the ends and split, but typically they can just be trimmed and re installed.
That said, it is ESSENTIAL that when acquiring a new (to you) vehicle, one must take the factory service manual (FSM) and verify line by line that all the hoses are connected at the right point to the correct device.  The number of carburetors and distributors that have been changed because of disconnected vacuum lines somewhere down the circuit is criminal.
Short version: Get the FSM, go down the color coded vacuum lines one by one and verifuy there are no disconnects or breaks in the lines and 95% of the "issues" will disappear.
That's my story and I'm sticking to it.
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
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Offline savemy67

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  • Name: Christopher Winter
Re: Checking the (gulp) vacuum system on a 1967 Eldorado?
« Reply #4 on: June 17, 2017, 08:49:27 PM »
Hello sdownie,

Both Greg and Scot make a good point about having the shop manual.  I own a '67 Sedan DeVille and the manual has a vacuum diagram showing what is connected regarding the engine and A/C systems.  The separate Fisher Body manual has diagrams for power locks.

Have you tried removing the seats to ease your efforts at getting under the dash?  It may be a toss-up whether it is easier to remove the dash pad or remove a seat to provide good access to the maze of connections under and behind the dash.  Good luck.

Respectfully submitted,
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

Offline Jeff Rose CLC #28373

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  • Name: Jeff Rose
Re: Checking the (gulp) vacuum system on a 1967 Eldorado?
« Reply #5 on: June 17, 2017, 11:00:39 PM »
The AC is its own separate issue.
For the vac, you can disconnect and plug the main vac lines off the carb and manifold. See if the car idles better. If so then you have a serious vac leak that needs to be corrected (or plugged) relatively soon. If not then it is something that can probably wait until it is cooler outside and you can get under the dash.
Don't butcher the climate control system. Read the manual and/or get Cadillac Tim's book. My temp control doesn't work either ( have to get $$ to buy a new head) but by reviewing the book I can get low and hi blower speeds with the ac *I am sire Scot just cringed).Works good enough for now. If I can do it, you can too.
« Last Edit: June 18, 2017, 08:50:37 AM by Jeff Rose CLC #28373 »
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1970 Coupe DeVille
1955 Series 62

Online 67_Eldo

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  • Name: sdownie
Re: Checking the (gulp) vacuum system on a 1967 Eldorado?
« Reply #6 on: June 18, 2017, 10:56:47 AM »
I do have the 1967 shop manual and 1967 Fisher body manual. They have been very helpful!

That's a good point about starting with the carb and working outward. In addition to the disconnected hoses I can feel (but can't see) under the dash, I know the headlight covers, for example, can get confused, going up when they're supposed to go down (occasionally).

I am going to try to eliminate as much vacuum-driven stuff as possible over time (e.g. use electric linear actuators for the headlights like this Toronado person did - ), but the lion's share of the vacuum system must remain.

The front bench seat is so heavy that I can't move it much. But maybe even moving it a little bit will help, so I'll give it another shot.

The dash pad came out with no problem. It is amazing how messed up the external vinyl looks while the fundamental pad frame looks great. The duct work for the passenger-side apparently melted and broke, but it isn't a big deal (if I can find replacement parts).