thinking about 78 eldo

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500, 472, 425, 368 Discussion, thinking about 78 eldo in Cadillac Engine Discussion; I've always really admired the 70's caddies, but I've only owned newer ones. I have an 02 deville that I ...
  1. #1
    soccer_eldorado is offline Cadillac Owners Fanatic
    Automobile(s): 02 Deville, 99 deville - both Adriatic Blue
    Join Date
    Jun 2004
    Miami Florida

    thinking about 78 eldo

    I've always really admired the 70's caddies, but I've only owned newer ones. I have an 02 deville that I really like, but it really seems like if you've driven one of them, you've driven them all. I know about a pristine 78 eldo for a good price that is yellow, perfect shape, but I'm concerned about that older transmission, I'm guessing they are front wheel drive. Any advice, I have a lot of experience working on my Northstar cadillacs, which overall have been reliable enough.

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  3. #2
    BRUCE ROE is offline Cadillac Owners Fanatic
    Automobile(s): Eldorado
    Join Date
    Jun 2009

    Re: thinking about 78 eldo

    Generally, the FWD THM425 and RWD THM400 transmissions are about the toughest & most reliable ever put in a car. They were used in all Cadillacs through 1978, RWD through 1981. If the mileage isn't too high, they usually don't show much wear. HOWEVER, these are now some 3 decades old, and some of the rubber parts (esp high pressure piston seals) may be hardening & about ready to let go. I drive these transmissions every day, but mine all received a new seal set. That isn't trivial, but still considerably short of a
    complete overhaul. 78 is a good year in my opinion. Bruce Roe CLC # 14630

  4. #3
    awadecki is offline Cadillac Owners Enthusiast
    Automobile(s): 76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
    Join Date
    Jun 2005

    Re: thinking about 78 eldo

    I personally wouldn't worry about the transmission. The THM425 (the transmission in the 78 Eldorado), is basically a THM400 that's split after the torque converter and flipped around to drive the front wheels. In other words, it's bullet proof.

    I own 3 of these Eldorados (two 1976s -both with around 50k miles a 1978 Biarritz wiht 9k miles). One of my 76 Eldorados is my daily driver. I've put 10k miles on it without issue. I did, however, change ALL fluids in each car when I bought them, including the trans fluid and filter.

    You should be prepared, however, for saggy doors, leaky A/C seals, some minor climate control issues (I've always easily resolved mine), and poor stereo speakers.

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