Opinion wanted on purchase of 1978 or 1979 Coupe DeVille
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500, 472, 425, 368 Discussion, Opinion wanted on purchase of 1978 or 1979 Coupe DeVille in Cadillac Engine Technical Discussion; Hi everyone, I am interested in acquiring either a 1978 or 1979 Coupe Deville. How does maintenance and reliability of ...
  1. #1
    jfontana is offline Cadillac Owners Member
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    Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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

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    ferrisworld is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  4. #3
    gornati's Avatar
    gornati is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    On mine 78 i have EFI and discs on all 4 wheels, looks factory for me.

  5. #4
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  6. #5
    ferrisworld is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

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    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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)

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    jfontana is offline Cadillac Owners Member
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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

  9. #8
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    I meant to include '79 in that post. Must have mistyped.

  10. #9
    jfontana is offline Cadillac Owners Member
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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

  11. #10
    ferrisworld is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    And 75-76 too. Then 1980 - 1981 EFI used TBI, as did the 82 - 85 ht4100.

  12. #11
    jfontana is offline Cadillac Owners Member
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Quote Originally Posted by ferrisworld View Post
    And 75-76 too. Then 1980 - 1981 EFI used TBI, as did the 82 - 85 ht4100.
    got it.

    thanks,

    Jay

  13. #12
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    75-79 used one injector per cylinder, port injection. Bruce Roe

  14. #13
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  15. #14
    jfontana is offline Cadillac Owners Member
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Quote Originally Posted by The Ape Man View Post
    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

  16. #15
    jfontana is offline Cadillac Owners Member
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Quote Originally Posted by The Ape Man View Post
    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

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