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'76 Cadillac Acceleration

Started by Jeff Moffo, December 29, 2014, 08:07:51 PM

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Jeff Moffo

Good Evening,
Just wanted to get some feedback from fellow 500 cu in. engine folks.

I was lucky enough to get my Cadillac out of the garage this week in NJ, as the weather has been great. Car started great.  Idled great. Curb idle is exactly at 650 rpm.  Took it out on a 15 mile ride along some local roads and highways.  The car cruises at 65-70 mph effortlessly.  It shifts effortlessly as well....although once in a blue moon the shift from first to second is a little hard.  My only question is how should the acceleration from a stop behave on this car?  I understand the 5200 lb weight, and the fact that she is built for luxury and not performance!  I have read countless articles about how slow the acceleration is but also wanted to see if others who drive these cars experience the same.
I have owned this particular '76 for 14 months, and it has 35,000 original miles.  I did own another '76 that I sold about 6 years ago, yet I cannot recall how its acceleration was back then...although I am thinking I experienced the same. :-\

Thanks and Happy New Year to all.
Jeff
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

Scot Minesinger

Jeff,

You know Maurice's 1976 Fleetwood, and I would describe that as fun.  It certainly does not seem slow.  To give you some perspective my son thought the performance of a 472/500 better off the line than a 5.3 Chevy truck circa 2009 for example.

Scot
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

James Landi

If you'd like a more responsive launch, connect the vacuum advance directly into a matching sized intake manifold hose barb.  There's a speed modulator electromagnetic vacuum valve that does not permit the vacuum advance on the distributor to work until the car gets moving and is at speed... the result is a sluggish response.   I'd check the vacuum advance on the distributor to ensure that it will hold vacuum and that it moves the stator plate in the distributor, and then just try "teeing it" into the intake manifold... then take it for a drive.  You'll experience the difference immediately.

"Cadillac Kid" Greg Surfas 15364

JHeff,
How big is a breadbox?  In actual numbers a well tuned, good running 76 coupe deVille (mine did it with its new engine) should run the quarter mile in just about 15 seconds.  I hope that answers your question.
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-

Jeff Moffo

#4
I will try connecting the vacuum advance that way next time I get it started and out...
Looking at the vacuum advance on mine makes me wonder as it looks OLD, yet that does not mean it is not functioning correctly.

Now, I'm curious to know if there is something else that might be wrong.  Don't know if the big girl would do the 1/4 in 15 though...
Or maybe I'm worrying too soon!
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

TJ Hopland

The system James is describing I think was like 70-72 ish.   I don't think it ever came back unless they did a similar thing with the computers in the 80's.   

It is a good idea to take a look at the distributor to make sure its all working.   The GM HEI's it was really common to see the weights get stuck under the rotor.   Its easy to see them just lift the cap off (with wires still attached) and then remove the rotor which is attached with 2 screws.   You can then clearly see the springs and weights.     A little rust is normal and does not hurt anything.

The other thing to check is to see if the vacuum advance is still working.  At this age very little chance an original 'can' would still be working.   Easiest way to check it is with a hand vacuum pump.  If you don't have that you can try to move it manually and plug the vac port with your finger and see if it holds but I have found that to be difficult to do with the distributors.

If the weights are stuck and the vacuum not working the performance will be pretty flat.    On my first 500 I got that stuff fixed and on my first test drive getting on the freeway just about put it in the ditch when I floored it and lost traction. 
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

R Schroeder

I would also be checking that your heat riser , on the exhaust , isn't stuck shut.
Roy

"Cadillac Kid" Greg Surfas 15364

Jeff,
A real good way to check the "performance" of a '76 would be in the gas mileage.  If you are getting less than about 11 MPG there is something wrong.  One of the first things to go on this car would be the Catalytic Converter.  When they plug up performance (including gas mileage) drop off rapidly.
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-

cadillacmike68

I'm sorry, but 1974-76 Cadillacs and good acceleration are mutually exclusive terms.  :P
Regards,
"Cadillac" Mike

Jeff Moffo

I know!  I guess I'm not driving a Stingray, right?!
I do believe there is some issue however with its performance because it is a bit "too slow" to get going. Once moving, it is definitely performing where it should be.  I'll take a peak at the distributor and also the exhaust valve - that I'm sure has never been changed. As far as the distributor, I know they did replace plugs and wires about 4,000 miles ago but would have to check paperwork on what they did to the cap/rotor/timing.
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

Jeff Moffo

Took a picture of the distributor and weights. They look clean. Now to see if I can apply vacuum to the advance and see what happens. Now where did I put that vacuum gauge?!
By the way anyone know an "easy" way to access the heat riser. My God it seems so far away!!
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

TJ Hopland

Looks fairly clean.  Did you try pulling on the weights to make sure everything moves?  If you pull out on the fat part everything should smoothly rotate and then pop back when you let go.   A few times I have had the whole hub part size on the shaft. 

On the heat riser the only idea I have is to trade it in for an Eldorado, the FWD configuration puts the engine up higher and a lot further from the firewall.    Once you find your vacuum gauge / pump you can try hooking it to that line.  You can usually hear them moving.  If it moves then the next check would be to check the vacuum line when its warmed up to make sure there is not vacuum there.
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

Jeff Moffo

Weights move fine. Will check the vacuum advance next then head over to that EFE valve buried deep! 
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

James Landi

A simple test of the vacuum advance is to simply connect a hose to it, and suck on the other end.  Not the most hygienic approach, but if it has a leak, you'll know immediately.   Quite often, a faulty advance will cause you to lose gas mileage and brisk acceleration.  Most folks don't notice the difference once it fails, but having that advance working after you've replaced it will make you very happy.

mgbeda

The biggest difference between the 75-76 and earlier Caddies was the super-high rear axle - 2.73:1.  '74 and earlier had 2.98:1.  It made a big difference in feel.  (I know because Bessie at some point ended up with an earlier model rear axle and as a result was much quicker than the other three '76 Caddies I've owned.)

They had about average quickness in their day, but cars in general were pretty slow in the mid-70's.  They should probably do 0-60 in about 12 seconds, and might or might not chirp the tires on take-off.

The EFE valve won't really change anything.  Those only operate for a few minutes when the car is dead cold, then the vacuum to them shuts off, and the EFE valve opens.  They usually get stuck in the warm (open) position, since that's how they spend 99% of their life.  If they somehow get stuck closed it could cause pinging or maybe even overheating, but not slowness.  HOWEVER their plumbing could cause vacuum leaks, and those will affect performance.  Easier than digging down to that valve is just to disconnect the line between it and its thermal switch (located at the front of the engine, near the distributor).  Then with a vacuum pump / gauge you can see if the valve holds vacuum.  Or just plug the hose from the carb to the thermal switch and see if it makes a difference.

It's common for the centrifugal advance to get stuck, but it sounds like you checked that.  That also doesn't affect the off-the-line performance that much, though it can take down the gas mileage, or cause pinging, depending where it gets stuck.

The vacuum advance does have a big effect on the acceleration.  Again vacuum leaks anywhere in the car will affect how well the vacuum advance reacts.  These cars have a real maze of vacuum lines, all of which like to leak.  And often over the years vacuum leaks get compensated for by tweaks to the carb and timing, which end up degrading performance.  Checking all the hoses is the best, cheapest (though time-consuming) way to get the car running its best.

-mB
-Mike Beda
CLC #24610
1976 Sedan DeVille (Bessie)

Jeff Moffo

Well. I hooked up a vac line to advance and sucked like crazy. Can't find my vacuum gauge. Nothing- except I nearly turned blue. Nothing moves at all. I assume that is bad!?  I suspect I should attempt a true gauge and go from there. It's simple to change that advance can , right? 
Mike, no pinging or overheating so I am going to leave that darn EFE Valve temporarily. By the way. My hose from the carb leads to a tee, then splits to the can and the thermal switch. The EFE has its own line to that switch. Should I plug that line when testing?
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

TJ Hopland

Do you have a shop manual for that car?   I wonder if things are plumbed correctly?   What you are describing does not sound stock, not for sure wrong but not stock.   I'm just guessing since I don't have a 76 or even a 76 vacuum manual in front of me.    Maybe you have a fairly simple plumbing issue with the vacuum lines or possibly a failed vacuum control do dad and someone in the past has tried to mask the problem instead of fixing it. 

I used to be able to suck hard enough to operate a vacuum advance but I can't anymore so I would not consider that a good test.   May be worth a trip to a parts store or an 'import' tool store if you have one near you.  I have seen those little vac pump gauge setups complete with brake bleeding hoses for under $20.   May not last forever but its not like its a critical tool that you will use every day and could damage what you are working on.

Another thing that will make the performance kinda flat is if the secondaries are not opening on the carb.   Several things can keep them from opening and it varies a bit between different models of carbs so we can go into that later if the vacuum project does not lead us to a problem.   



Quote from: mgbeda on December 30, 2014, 03:14:21 PM
The EFE valve won't really change anything.  If they somehow get stuck closed it could cause pinging or maybe even overheating, but not slowness.

I do agree that its not common for them to get stuck closed but I have seen them get hooked up wrong so they do operate all the time.  Having it closed blocks the exhaust flow from being able to leave the exhaust manifold so its only choice is to leave through comparatively tiny holes in the head and then through the fairly small exhaust cross over in the intake and then through the same tiny holes in the drivers side head before finally being able to get into the manifold and make the trip out to the tail pipe.   Its quite a restriction and will definitely take the edge off performance.    The compounding problem is the extra heat which like you said can lead to detonation and other issues.  First thing most people do with a detonation issue is retard the timing which also tends to flatten the performance.   
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

The Tassie Devil(le)

When you test the vacuum advance, put a hose directly to the vacuum advance diaphragm and then suck on that only.   Forger about the rest of the system, as trying to suck on everything else will surely turn you blue.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

cadillacmike68

Quote from: mgbeda on December 30, 2014, 03:14:21 PM
The biggest difference between the 75-76 and earlier Caddies was the super-high rear axle - 2.73:1.  '74 and earlier had 2.98:1.  It made a big difference in feel.  (I know because Bessie at some point ended up with an earlier model rear axle and as a result was much quicker than the other three '76 Caddies I've owned.)

They had about average quickness in their day, but cars in general were pretty slow in the mid-70's.  They should probably do 0-60 in about 12 seconds, and might or might not chirp the tires on take-off.

The EFE valve won't really change anything.  Those only operate for a few minutes when the car is dead cold, then the vacuum to them shuts off, and the EFE valve opens.  They usually get stuck in the warm (open) position, since that's how they spend 99% of their life.  If they somehow get stuck closed it could cause pinging or maybe even overheating, but not slowness.  HOWEVER their plumbing could cause vacuum leaks, and those will affect performance.  Easier than digging down to that valve is just to disconnect the line between it and its thermal switch (located at the front of the engine, near the distributor).  Then with a vacuum pump / gauge you can see if the valve holds vacuum.  Or just plug the hose from the carb to the thermal switch and see if it makes a difference.

It's common for the centrifugal advance to get stuck, but it sounds like you checked that.  That also doesn't affect the off-the-line performance that much, though it can take down the gas mileage, or cause pinging, depending where it gets stuck.

The vacuum advance does have a big effect on the acceleration.  Again vacuum leaks anywhere in the car will affect how well the vacuum advance reacts.  These cars have a real maze of vacuum lines, all of which like to leak.  And often over the years vacuum leaks get compensated for by tweaks to the carb and timing, which end up degrading performance.  Checking all the hoses is the best, cheapest (though time-consuming) way to get the car running its best.

-mB

Besides the above, the compression ratios dropped like a lead balloon starting 1971. In 1970 the dropped to 10:1 (68 & 69 were 10.5:1), but power remained the same. Then there were the strangled carbies with capped non-adjustable idle mixture screws, etc.. Give me a 1968-1970 any day. I do like the 1971-72 Eldorado Convertibles though...
Regards,
"Cadillac" Mike

Jeff Moffo

Bruce,
I placed a vacuum hose only on the advance canister to suck through to see the effect on the mechanism.  Nothing. Actually could barely get any suction at all sort of like sucking a hose that was blocked.

TJ,
I do have a manual with its vacuum diagram and mine match exactly. So the plumbing is not the issue.

Off to get a vacuum gauge tomorrow sometime. Mine grew legs I guess.
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green