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1965 Cadillac rough idle

Started by Scot Minesinger, June 24, 2018, 08:09:26 PM

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Scot Minesinger

1965 SDV, 429 with 127k miles, same owner last 20 years.  At 90k miles a valve job was completed about 21 years ago.  The car has always suffered a rough idle.  The owner is interested in driving and enjoying it.  Recently the carb had to be rebuilt and the timing chain was replaced - it was way past due.  The idle is still rough, and so here is the situation and work performed:

1.  Timing chain replaced (and set timing) all visible chips of nylon removed and the re were a lot of them all over.
2.  Installed rebuilt carb per shop manual (Carter)
3.  Replaced spark plugs and wires
4.  Replaced numerous vacuum hoses
5.  Car was converted to electronic ignition previously
6.  fuel pump replaced (not that this matters)
7.  Replaced valve cover gaskets and did not see any valve train issues.
8.  The heat riser damper blade inside the exhaust pipe was removed so it looks authentic, but free flowing exhaust always.
9.  The compressor is noisy even with clutch not engaged and I am going to look at replacing it.

Car runs great, plenty of power and at speed it is awesome.

Any ideas on smoothing out the idle that the 429 folks may have some good experience with?

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

cadillactim

Scot

Check for vacuum leak. Slowly cover carb with your hand and see if idle improves. If it does likely vacuum issue.

Tim
Tim Groves

pplaut

Thanks for the tip on covering the carb with your hand to see if idle improves. Later year, but sometimes I get a rough idle but only in gear.
Peer L. Plaut
Head Baldie
Baldmen.Com

savemy67

Hello Scot,

I gather form your post that the car runs great at any speed above idle.  If we consider the carburetor as a likely suspect, do you know how good the rebuild is?  Is there any slop in the throttle shaft where it passes through the throttle body?  Were the idle screws replaced?

If we consider a vacuum leak, your post mentioned that numerous vacuum hoses were replaced.  What about the hoses that weren't replaced?  What is the condition of those hoses?  What is the condition of the vacuum actuated devices to which all the hoses are attached?

If we consider the ignition, does the rough idle involve a mis-firing cylinder (a cylinder balance test might uncover this)?  What is the condition of the distributor shaft, mechanical and vacuum advance assemblies?

If the car needed a valve job 21 years and 37,000 miles ago, have you done a compression or leak-down test?

Respectfully submitted,
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

Jeff Rosansky CLC #28373

I have the same issue with our 70. Runs like a scalded cat at anything above idle, but it idles like crap. I was actually going to bring it home yesterday to finally pull the carb but I had a brake light for the first time. Rear reservoir empty. Found both rear cylinders leaking so that project moves to the front of the line.
When you are checking for leaks don't forget about the brake booster. Mine was idling worse than usual and actually had a  water temp light that came on after getting gas which isn't overly surprising on a hot day but it didn't go off immediately. Found the plastic check valve at the booster had a Crack in it.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

Cape Cod Fleetwood

The Ark has a pretty rough idle too, I'm just grateful it runs smoothly when under power. New plugs, wires, fuel fliter, carb filter cleaned out, new air filter, condenser, also electronic ignition, runs on Sunoco 93. Any reason not to put a bottle of Techon Concentrate in it? I have 1 vacuum line to replace for sure, and my mech is begging me to take it up on Route 6 and just pin it for few miles to blow it out. All it takes is time....

\m/
Laurie
There are 2 kinds of cars in the world, Cadillac and everything else....

The Present -1970 Fleetwood Brougham

The Past -
1996 Deville Concours
1987 Sedan De Ville "Commonwealth Edition"
1981 Coupe De Ville (8-6-4)
1976 Sedan De Ville
1975 Sedan De Ville

The Daily Driver and work slave -
2008 GMC Acadia SLT *options/all

Mike Josephic CLC #3877

If you are going to use a fuel system additive, Techron
is one of the best.  It's actually used as a fuel system
additive by some of the major gasoline producers.
Developed by Chevron.

Mike
1955 Cadillac Eldorado
1973 Cadillac Eldorado
1995 Cadillac Seville
2004 Escalade
1997 GMC Suburban 4X4, 454 engine, 3/4 ton
custom built by Santa Fe in Evansville, IN
2011 Buick Lucerne CX
-------------------------------------
CLCMRC Museum Benefactor #38
Past: VP International Affiliates, Museum Board Director, President / Director Pittsburgh Region

cadillactim

When the engine idles rough at idle, but runs  fine otherwise, often times there is too much air in the fuel mixture, aka vacuum leak. Off idle the mixture is more balanced since more fuel is being drawn in. That said, maybe focus on the carb adjustments, wear in the throttle plates shaft, intake manifold cracked or choke tube leak inside manifold, distributor vacuum advance, as well as brake booster which was mentioned before.

Tim
Tim Groves

Bryan Thompson

Good morning, This one may sound stupid but, my 67 DeVille FoldyTop had a rough idle issue that went away by itself when we were driving on a 97 degree day.  I noticed that the temp gauge went to the first hashtag.  It usually didn't move up much at all. So I decided to have a look at the thermostat.  When I took it apart the thermostat was in upside down and was stuck open.  Put in a new 195 degree stat, rough idle has mostly 95% gone away. :-) Guess she like to run at the temperature Cadillac engineers wanted.
I would rather push an old Cadillac, than drive a new anything:-)

Mike Josephic CLC #3877

One comment about an earlier posting.

Covering the carb using your hand is never a good
idea.  If that engine "burps" (backfires up through
the carb) you'll get a nasty 2nd or 3rd degree burn.

I've seen it happen -- almost happened to me once
-- then I decided to get smart.  Not worth a trip to
the ER.

Mike
1955 Cadillac Eldorado
1973 Cadillac Eldorado
1995 Cadillac Seville
2004 Escalade
1997 GMC Suburban 4X4, 454 engine, 3/4 ton
custom built by Santa Fe in Evansville, IN
2011 Buick Lucerne CX
-------------------------------------
CLCMRC Museum Benefactor #38
Past: VP International Affiliates, Museum Board Director, President / Director Pittsburgh Region

cadmium

#10
About #9, the compressor being noisy even with the clutch not engaged, that is the pulley bearing going bad and if let go it will get too hot and burn out the front seal in the compressor dumping all the freon out and creating a lot of expense and hassle to fix it.  That bearing can be replaced without opening up the freon system and it's not necessary to replace the entire compressor either.  Get the clutch tools and pull the clutch.  I recommend fixing that while it's still an easy and inexpensive fix before it creates worse problems.
1968 Coupe deVille
1968 DeVille Convertible

Scot Minesinger

Thank guys, some things here I have not tried and so it is printed out and will take a look it this weekend.

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

64\/54Cadillacking

My 64 Cadillac has a 65 motor in it and for the longest time the idle has been very iffy and rough at times as well.

One thing that did make a slight difference in the idle was using Autolite 85 spark plugs.

I used Champions, AC Delco’s and Bosch, and the engine hated the first 2! hands down the Autolites 85 made the engine run smoother. So try switching out plugs and see if that helps.

Also, if you do have any vacuum leaks that will cause problems. I still need to replace the intake manifold gasket since there’s a leak.

I plan on getting an Eldelbrock Carb to replace the Carter that’s on it now. I had the Carb rebuilt and for some reason it keeps seeping out gas near the base of the Carb and I can’t figure out why. I adjusted the floats and it still leaks. The throttle shaft plates could be worn, but I’m tired of messing with it, so the eldelbrock is going is soon going in soon.
Currently Rides:
1964 Sedan Deville
1954 Cadillac Fleetwood 60 Special
1979 Lincoln Mark V Cartier Designer Series
2007 Lexus LS 460L (extended wheelbase edition)

Previous Rides:
1987 Brougham D' Elegance
1994 Fleetwood Bro
1972 Sedan Deville
1968 Coupe Deville
1961 Lincoln Continental
1993 Lincoln Town Car Signature Series
1978 Lincoln Continental ( R.I.P.) 1978-2024 😞

Scot Minesinger

It was the harmonic balancer.

When the timing chain was off the rubber seemed suspect on the balancer.  The idle was almost mechanically rough.  Changed it out with a brand new one and it is much smoother. 

No vacuum leaks, if you put your hand across the carb it will stall before it gets smoother.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Cape Cod Fleetwood

Quote from: Scot Minesinger on August 07, 2018, 11:03:00 PM
It was the harmonic balancer.

When the timing chain was off the rubber seemed suspect on the balancer.  The idle was almost mechanically rough.  Changed it out with a brand new one and it is much smoother. 

No vacuum leaks, if you put your hand across the carb it will stall before it gets smoother.

Scot if the pulley on the power steering pump is a little funky, won't that in turn 'throw off' the harmonic balancer? Asking for a friend...

\m/
Laurie
There are 2 kinds of cars in the world, Cadillac and everything else....

The Present -1970 Fleetwood Brougham

The Past -
1996 Deville Concours
1987 Sedan De Ville "Commonwealth Edition"
1981 Coupe De Ville (8-6-4)
1976 Sedan De Ville
1975 Sedan De Ville

The Daily Driver and work slave -
2008 GMC Acadia SLT *options/all

"Cadillac Kid" Greg Surfas 15364

Laurie,
The crankshaft pulley is attached to the hub which is solid with the crankshaft. The actual "harmonic balancer" is an iron ring which rides on an isolating "biscuit" between the hub and the damper ring.  I believe there are 3 or 4 engine/year specific dampers for the 429 since the timing mark locations vary, and there are three possible mountings for the damper ring, leading at times to some confusion, inaccurate timing and rough running.
Funkey is one of those highly technical terms, but I am assuming you mean the pulley is  not straight. That typically leads to noise, vibration nd premature belt or pump failure.
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

Laurie,

Surprisingly, the power steering pump pulley is important to a smooth idle.  I replaced one on a 1974 Cadillac that a prior mechanic had bent.  If you looked on from driver side fender hood open car running, you could see the wobble in the pulley of about an 1/8 to 1/4 inch.  After it was replaced the car did idle smoother.

If the pulley is bad, not only will it prolong belt life, it should smooth out idle.

If in doubt just disconnect the belts and remove - then start car should be smoother.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Jeff Rosansky CLC #28373

Quote from: Scot Minesinger on August 07, 2018, 11:03:00 PM
It was the harmonic balancer.
How does one check the balancer? Is it different on say a 70? Like Laurie I am asking for a "friend" who just happens to have a car exactly like mine(same color actually) with a rough idle.... and I happen to have the keys to it. ;)
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

"Cadillac Kid" Greg Surfas 15364

Jeff,
If the harmonic balance is defective you should hear it rattling at idle.  If you don't hear anything, WITH THE MOTOR OFF, see if you can wiggle the outer ring of the balancer (where the timing marks are).  If you can move it it needs replacing.
74 and later have a single piece cast balancer/pulley, so although they can become loose, they don't fail.
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

Jeff,

If your harmonic balancer is bad, it is easy to replace, because it is a disk bolted to the crank thru the drive pulley.  The 429 has a one piece hub and balancer combo pressed onto the crank shaft.  The rough idle is more uniform and reliable with a mechanical imbalance, such a bent pulley or bad harmonic balancer.  With a vacuum leak it is not even and rough with no rhythm.  I bought a new one from Cadillac King.  On a 472 I would buy from MTS.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty