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500, 472, 425, 368 Discussion, Opinion wanted on purchase of 1978 or 1979 Coupe DeVille in Cadillac Engine Technical Discussion; The axle being used as the race isn't really a big deal. That's the same on the other GM rear ...
  1. #16
    jayoldschool's Avatar
    jayoldschool is online now GM RWD V8 addict
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  2. #17
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Quote Originally Posted by jayoldschool View Post
    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.

  3. #18
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  4. #19
    WWlll's Avatar
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    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...

  5. #20
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Quote Originally Posted by jfontana View Post
    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.

  6. #21
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  7. #22
    The Ape Man's Avatar
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Factory injection runs a whole lot better than a carbonator especially on Cadillac engines. Night and day.

  8. #23
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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

  9. #24
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    Quote Originally Posted by BRUCE ROE View Post
    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.

  10. #25
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

  11. #26
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    A 500 can idle at 300 RPM in drive with the 1975 injection system. Try that with a carbonater.

  12. #27
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Opinion wanted on purchase of 1978 or 1979 Coupe DeVille

    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.

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