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74 fleetwood vacuum advance not working

Started by ithaca1230, June 15, 2017, 08:54:12 AM

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Spent a couple hours with the mechanic yesterday changing the points and trying to get the old girl tuned up and running correctly. One thing that we found was the Vacuum advance on the distributor was not working. What do you guys recommend. Is this part replaceable or should we replace the whole distributor. While we were there we replaced most of the old vacuum lines that were dried up. Car runs good with all new wires plugs cap rotor.
Billy Epthimiatos


Would say you should be better off changing to an electronic ignition and a new coil

Here is a way to do it on a car that is 10 years older than yours:

Now I have to admit I am not sure how the -74 distributor is designed. But normally its very easy to replace the vacuum advance and cost of a new one is low. Use a vacuum pump if the screws are hard to get too.


Hey thanks! I will do some reading on this and see if it is something I can do myself.

"Cadillac Kid" Greg Surfas 15364

The Vacuum advance is a replaceable part.  They are essentially exposed to gasoline vapor (via the vacuum connections) and have a limited lifetime.  Replacement is a very common task.
Even if you convert to another type of ignition you will still need a vacuum advance for temperature control, fuel economy and idle stability.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Scot Minesinger

I have three 1970 Cadillacs, two with electronic ignition conversion, the other with points and condenser, and while the conversion made absolutely no difference in performance or anything, the one remaining points and condenser Cadillac is the best running of the three.

BTW as Greg wrote that vacuum actuator is replaceable, and easily done.  The part is readily available.  Electronic ignition was an option in 1974 (first year).
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty


I would like to order order a new vacuume advance but I'm having trouble sourcing one any suggestions.


Jeff Rose CLC #28373

While it more than likely needs to be replaced, it may just be frozen if it sat long. Hook a vac hose up to it and suck. If it holds vac then it may be good. If it like suckling thru a skinny straw (think coffee stirrer) then the diaphram is bad and needs replacing. If it is good then try to get it all moving in the distributor and lubricate. Don't get any lube on/around the points. However be prepared to replace it.
Jeff Rose
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

TJ Hopland

What usually causes you to have to replace the whole distributor is wear in the bushings or shaft.   An indicator of the condition is how steady the dwell reading is.   A badly worn distributor the dwell will tend to jump around especially as the rpms change.   A solid distributor the reading will remain steady.   Sometimes the weights and such can have issues but that didn't seem to be a problem with the points style, more common on the later HEI. 

Replacement vacuum canisters these days seem to be a one size kinda fits most sort of thing so looking for a 'performance' model that is adjustable as far as the amount of travel may be best so you can try and duplicate the original specs.   There should be several options.   I believe the top of the GM V8 distributors was pretty standard from the late 50's early 60's till the end.   It was the bottom that was different to fit different engines and then the 'tune' that varied.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason


I would like to replace it just can not find one I am sure will fit the car.


Be sure to set that adjustable vacuum advance up with a tachometer and timing light according to the specs in your Cadillac factory shop manual or you may well have moderate to severe pinging like another poster here recently wrote about.  It should go without saying that ours are not SBC Chevy engines and do not respond well to the kind of aggressive advance a Chevy will. 
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

James Landi

Is the '74 vacuum advanced hooked up to a vacuum break that does not engaged unless the car is up to speed (my '70 and '72 had the arrangement)?  IMHO-- taking the advance and running the vacuum directly to the manifold gives these model cars a much more response engine response (i.e. taking the vacuum break out of the circuit).  James Landi

TJ Hopland

73 they got rid of that speed limit vacuum solenoid dodad.   The second part of that was a little gearbox thing hanging off the side of the transmission with the speedometer attached to it.    74 Likely just had the thermal vacuum switch kinda near where the distributor goes into the block that changed between ported (carb) vac and manifold vac depending on coolant temps.    Those switches often don't seem to be working properly at this age.   I have seen them stuck and plugged up not passing any vacuum as well as having vacuum on all 3 ports at the same time.  Never took one apart to see how that is even possible.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason