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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, 78 in Past Cadillac Vehicle Discussion; I recently bought a tumble-down 1978 Cadillac Deville base model. It needs a lot of work, but first I need ...
  1. #1
    Jason5 is offline Cadillac Owners Member
    Automobile(s): 1978 Cadillac Deville, 1988 Cadillac Brougham
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    78

    I recently bought a tumble-down 1978 Cadillac Deville base model. It needs a lot of work, but first I need to bolt on the exhaust system and install a new flexplate.

    How would I go about installing a flexplate myself on an automatic THM400 transmission/7.0L L35 engine combo? I have a good jack, and two jackstands available, as well as an assortment of tools and a friend who knows about as much as me (i.e. enough to change the oil and tranny fluid.. not much else)

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  3. #2
    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: 78

    Remove splash shield, take out torque converter bolts, shove converter back in trans, remove exhaust, remove driveshaft, support trans, remove trans mount nut, remove trans crossmember, disconnect trans cooler lines and linkage/electrical, remove bell housing bolts, lower trans on jack. That TH400 will be heavy, be careful. Remove flex plate bolts, replace flex plate, use loctite and torque properly, put everything back in. I'm sure I have forgotten some details.

    This is a big job for someone who has only done oil changes.

  4. #3
    Jason5 is offline Cadillac Owners Member
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    Re: 78

    Yeah.... How long do you think it'd take a mechanic to do all that? I know a good mechanic with his own lift that charges 50 an hour, and the price is somewhat negotiable, I might just take it to him...

  5. #4
    csbuckn is offline Cadillac Owners Master
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    Re: 78

    A little trick, remove the two lower bolts that hold the tranny to the engine, get some 8 inch bolts of the same thread and screw them into the same spot, remove the driveshaft, unbolt the rear tranny mount, unbolt the torque converter, tranny to engine bolts, linkage, tranny lines and slide the tranny back on those 8" bolts till you have room to get the flexplate bolts. I've did this a couple times and it works great. When done, just slide the tranny back into place and bolt everything back into place. Might want to get under the car and see if this is something you want to do. What Jay says about Loctite and torquing to spec is important. I had a bolt come loose on me last year, thought it was a rod knock for a minute.

  6. #5
    lacville78 is offline Cadillac Owners Fanatic
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    Re: 78

    This is one of the reasons this forum is so great. You can't get better advice than what these two guys have said!

  7. #6
    csbuckn is offline Cadillac Owners Master
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    Re: 78

    Quote Originally Posted by lacville78 View Post
    This is one of the reasons this forum is so great. You can't get better advice than what these two guys have said!
    It is pretty cool. I learned that trick from another forum and it stuck with me. Unfortunately, I had to use it to redo my bad install in the first place. Torque the bolts! A lot of people underestimate torquing. If you have four bolts at 75lbs and two at 50lbs, those 50lbs bolts will be coming out soon. I didnt torque and I was back under the car three months later.

  8. #7
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: 78

    How do you know it needs a flexplate?

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