: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille



jfontana
09-04-12, 10:25 PM
Hi everyone,

I am interested in acquiring either a 1978 or 1979 Coupe Deville. How does maintenance and reliability of these particular year models rate vs the previous generation (1971-1976)? Is the 425 a good reliable engine? How common is it to find the fuel injected factory option of the 425 engine and what type of fuel injection was it? If not common, is it possible to convert a 425 with carburetor to sequential fuel injection? Are there any kits for this? Did either 78 or 79 models come with anti lock brakes? If not, are there kits to convert to anti lock breaks? Your answers would be greatly appreciated.

Thanks,

Jay

ferrisworld
09-05-12, 12:13 AM
Yes to everything except the brakes and commonality of the EFI option. You can find them but it's hard. I've been looking locally all year with no luck yet. But, the EFI is the same from 1975 to 1979 (only the injectors are smaller for the 77 - 79, and the computer is different), so it gives you a few years to look at for parts to convert it. For ABS you could get all the brake parts from a late model Fleetwood with ABS. I don't know that you would need the whole rear axle, but you might as well get it, and the front spindles. That's what I want to do eventually.

gornati
09-05-12, 06:58 AM
On mine 78 i have EFI and discs on all 4 wheels, looks factory for me.

deVille33
09-05-12, 10:37 AM
Bruce will tell you, the factory EFI would be the cheapest, most efficient way to go. Rear axle disc brakes were available on the Brouhams and as options on SDVs. from 1977 - 1978. Having kept my expertise within these three years, I can't tell you of the availability of such parts into the eighties, but I know rear disc brakes were not available prior to these years.
I can tell you that these cars will prove to be a most enjoyable experience for you. The one area that is problematic is the climate control unit. There are several posts here in regards to that system, it's problems, and several examples of how to coax it back into operation.
The TH400 transmission will sometimes be a problem. For the most part it is reliable, but if it needs a rebuild, it can be repaired for much less than any of the newer transmissions and will last longer too.
The 425 engine is a very formidable powerhouse, very enduring, and reliable. High mileage, may uncover a few problems, but for the most part, nothing serious, unless it had been abused.

ferrisworld
09-05-12, 12:29 PM
They had rear discs as an option in 1979 too, and many of the 1994-1996 B and D body cars. But no anti-lock except for 1994 - 1996.

BRUCE ROE
09-05-12, 02:07 PM
Those years can be a very reliable drive train, providing you catch up the maintenance. I drive
those years coast to coast, no problem. But you need to go through the brakes, I replace about every
thing that touches brake fluid; stainless lines & fittings will minimize future problems. All the rubber
& plastic, starting with vacuum hoses, then the timing chain (plastic teeth), a $28 rubber seal kit for
the TH400 (if you do it yourself), and check the gas tank & its hoses.

Any 425 or 500 EFI system will bolt on, the injectors & ECU from a 500 must be changed. These systems
have their own maintenance issues, starting with injector seals (40 psi + bad O ring = fire), and electrical
issues. These were quite a reliability issue, but they can be fixed. I have been working on beating down
the most common problems, not finished yet. But they run very well using batch injection, 4 of the 8
injectors alternately fired each crank revolution. Saw one on E*ay Item number: 300773524157

The 70s systems are easily converted to sequential injection, from a mechanical point of view. But you
will need a new ECU and need to put a long effort into getting it properly tuned. I did this to my 79,
but the tuning isn't finished yet. No easy kit available, roll your own. You can read about 70s EFI on
my PHOTOBUCKET, first SUB Album 70s FUEL INJECTION. good luck, Bruce Roe CLC# 14630
http://s93.photobucket.com/albums/l71/bcroe/

(that is a lower case "L"71, not an upper case "i"71)

jfontana
09-05-12, 03:37 PM
Hi everyone,

Thank you, to all that have replied. virtually all of my questions were answered.
Bruce, thank you for your info and the link to your Photobucket page. I find it to be very resourceful and I am sure I will refer back to it in the future. I am interested to know as to your progress with your sequential fuel injection system.

thanks in advance

Jay

deVille33
09-06-12, 08:56 AM
I meant to include '79 in that post. Must have mistyped.

jfontana
09-06-12, 10:08 AM
So just to clarify, the fuel injection systems from the factory, on models 77-79, were some sort of multipoint fuel injection system, not a tbi type, where the fuel is injected through a central point within the intake manifold?


thanks,


jay

ferrisworld
09-06-12, 11:16 AM
And 75-76 too. Then 1980 - 1981 EFI used TBI, as did the 82 - 85 ht4100.

jfontana
09-06-12, 03:55 PM
And 75-76 too. Then 1980 - 1981 EFI used TBI, as did the 82 - 85 ht4100.

got it.

thanks,

Jay

BRUCE ROE
09-08-12, 12:33 AM
75-79 used one injector per cylinder, port injection. Bruce Roe

The Ape Man
09-08-12, 04:55 AM
Real axle bearings on those years used the axles as races and were prone to wearing out much faster than earlier models.

That rear disc brake setup was a giant pain due to the emergency brake.

Better off with the drum brakes.

1980 and later booster/master cylinder makes a great retrofit to earlier models and was a redesign due to complaints of poor pedal feel.

jfontana
09-08-12, 04:31 PM
Real axle bearings on those years used the axles as races and were prone to wearing out much faster than earlier models.

That rear disc brake setup was a giant pain due to the emergency brake.

Better off with the drum brakes.

1980 and later booster/master cylinder makes a great retrofit to earlier models and was a redesign due to complaints of poor pedal feel.

good info, thanks again...

Jay

jfontana
09-08-12, 04:32 PM
Real axle bearings on those years used the axles as races and were prone to wearing out much faster than earlier models.

That rear disc brake setup was a giant pain due to the emergency brake.

Better off with the drum brakes.

1980 and later booster/master cylinder makes a great retrofit to earlier models and was a redesign due to complaints of poor pedal feel.

good info, thanks again...

Jay

jayoldschool
09-08-12, 05:12 PM
The axle being used as the race isn't really a big deal. That's the same on the other GM rear ends (10 bolts, both 7.5 and 8.5s, still used in trucks today). The rear discs work fine, but you MUST set the parking brake every time. That keeps the brakes adjusted.

deVille33
09-09-12, 12:57 PM
The axle being used as the race isn't really a big deal. That's the same on the other GM rear ends (10 bolts, both 7.5 and 8.5s, still used in trucks today). The rear discs work fine, but you MUST set the parking brake every time. That keeps the brakes adjusted.

In regards to this, I had sent an inquiry to Morrison's and they informed me that they could produce replacement axles for this housing, np. As it worked out, I took axles out of another housing, in better condition, so I did not need their services.

The Ape Man
09-10-12, 09:09 PM
The axles aren't impossible to deal with. Aftermarket offset bearings get more life frim worn axle shafts. Just one thing to look for on these cars. Especially when buying one because that could be the reason someone is dumping one.

WWlll
12-31-12, 11:52 PM
I have a 78 deville,,and I love her,,built to last...if u buy the car change out the oil pump very simple to do,,just find your oil filter,,the filter screws onto the oil pump.. the axles aren't hard to change out. Finding them may be difficult..I had to replace mine,,but I got lucky and found a set...

BRUCE ROE
01-01-13, 08:29 PM
I am interested in acquiring either a 1978 or 1979 Coupe Deville. How does maintenance and reliability of these particular year models rate vs the previous generation (1971-1976)? Is the 425 a good reliable engine? How common is it to find the fuel injected factory option of the 425 engine and what type of fuel injection was it? If not common, is it possible to convert a 425 with carburetor to sequential fuel injection? Are there any kits for this? Did either 78 or 79 models come with anti lock brakes? If not, are there kits to convert to anti lock breaks? Your answers would be greatly appreciated. Jay

Jay,
In my opinion these are as reliable as they come, for a car anywhere near that age. The TH400 is the strongest trans
ever put in a car. The 425 is excellent, with valve rotators, HEI, and internal reg alternator. Yes any car that age will
need updates, like all critical rubber & plastic parts (tires, brake/vacuum/radiator hoses, timing chain, trans soft parts,
etc) to be reliable. After that maintenance should be quite low.

A few were fuel injected, that is probably the most unreliable thing on those cars. All the rubber in the EFI must
be replaced or risk a fire. A lot of the issues with the EFI have been worked out, and some can be avoided entirely.
Since they are port injected, they are natural candidates for sequential injection. But that is a major, MAJOR project
that will require a lot of expertise, and put your car on hold for quite a while. I don't know of a sequential injection
425 kit, roll your own. However a MAF based kit (usually throttle body injected) could be done and working rather
quickly, and with good results. Note, the 70s used mechanical advance HEIs; an upgrade to electronically mapped
ignition timing would give a lot more bang & less down time, than a full EFI.

See some descriptions of late 70s EFI on varied sub albums of my PHOTOBUCKET.

http://s93.photobucket.com/albums/l71/bcroe/

(that is a lower case "L"71, not an upper case "i"71)

click on a Sub-Album
click on a picture to enlarge + explanation

Bruce Roe CLC # 14630, 70s EFI technician, driving 78 engines with carb, stock 78 batch injection, conversion to
sequential MAP injection, MAF injection, and carb with electronic spark map.

cadillac_al
01-02-13, 11:10 AM
In other words that EFI can drive you crazy lol. If you like to tinker with old tech just for the cool factor then you might not mind it. I used to tinker with mine back in the middle 90's before I even had a computer or internet or service manual to help me. It was always a bad connection somewhere. I got tired of it in 96 and just put a carb on it and I haven't had to tinker with it now for the last 15 years. I think it would be best to look for a carbed version for simplicity and reliability. If you buy EFI then at least we have Bruce to help you with it.

The Ape Man
01-08-13, 06:11 PM
Factory injection runs a whole lot better than a carbonator especially on Cadillac engines. Night and day.

BRUCE ROE
01-09-13, 02:24 AM
I thought the 1979 factory EFI ran better on my 350s & 403s, than a carb. But I
wouldn't say it was a spectacular improvement. Bruce Roe

The Ape Man
01-11-13, 03:59 PM
I thought the 1979 factory EFI ran better on my 350s & 403s, than a carb. But I
wouldn't say it was a spectacular improvement. Bruce Roe

Olds engines are smoother than Cadillac at and just off idle. Maybe its due to the uphill intake and aggressive spark lead on the Cadillacs.

I do not remember ever having a hard time getting an Olds V8 to idle perfectly with a Quadrajet. Cadillacs were always a different story.

deVille33
01-12-13, 11:03 AM
Perhaps that is the result of your expertize with Olds engines. By following the SM and other tune-up instructions carefully, I have had very good results setting up the QJ on a 425 engine. One problem with the Cadillac settings are the engine speed variables necessary to perform the operation. After each change in settings I would back up a step and do a reset of the timing/engine speed to ensure the engine was set at it's perscribed settings going into the next adjustment. It is a time consuming proceedure, but the results I got were an engine that ran at the proper idle and with good off idle response and relatively good mpg figures.

The Ape Man
01-12-13, 07:13 PM
A 500 can idle at 300 RPM in drive with the 1975 injection system. Try that with a carbonater.

deVille33
01-13-13, 11:59 AM
What is the suggested idle speed for the FI 500? I have had idle speed below 500 rpm with a carbed 425 in drive, but the set point was 550. These engines will idle at relatively low speeds in comparison to other engines due to the low cam lift, duration and lack of overlap that other engine designs rely on to perform. The FI systems used on these engines is undoubtedly superior. It was also a more costly option and not what most owners took. All in all, I have been impressed with Cadillac's engines and the torque they could produce.