Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help!!
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500, 472, 425, 368 Discussion, Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help!! in Cadillac Engine Technical Discussion; Hey and thanks to anyone who can help....My 1978, 425 engine runs good in Park but when I try to ...
  1. #1
    Tee53 is offline Cadillac Owners Member
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    Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help!!

    Hey and thanks to anyone who can help....My 1978, 425 engine runs good in Park but when I try to put it in Reverse or Drive its shifts hard and stalls!! I can shift it into Neutral and it continues to run. Does anyone have any idea of what this could be???

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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help

    Is the engine up to operating temperature when this happens? What you describe is generally vacuum related. Are the choke dashpots operating properly? Check your vacuum lines for cracks or splits. Your vacuum advance canister could have failed. The most useful tool to have at your disposal is a hand held vacuum tool, a Mighty Vac (Name Brand). They have inexpensive ones at Harbor Freight. Is there another driven unit pulling your power from the engine? Any belts squealing? Does the car move forward when you put it in gear? If it doesn't move, you may have a lock up in the transmission. A broken piston return spring can cause a clutch pack to stay engaged and work against your reverse pack. This doesn't happen often, so it is a remote possibility. More information would be useful in order to diagnose this.

  4. #3
    Tee53 is offline Cadillac Owners Member
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    Re: Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help

    Hey and thanks for the help!!! I have replaced the carb with a 600cfm edelbrock carb and removed all the vac lines except for the line from carb to transmission module. I am pulling about 16 -18 pounds when the car warms up. Should I put the vac lines back on???? It will move/jump back or forward when put in a gear and will continue to run good in neutral if I shift it fast enough. I did a compression check of the cylinders and all are running at 145 - 150 execpt for #8 gave me a 135... I have replace the gen the power steering pump and all the belts

  5. #4
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help

    I'm not getting it I guess. The car runs fine in park and stalls in gear? Can you idle it up or give it gas to make the car move? Is the Carb new or used? I usually hook the trans vacuum line directly to manifold vacuum. The Edelbrock carb has ported vacuum on the passenger side whereas the stock carb has it on the drivers side. I don't think that would cause your problem though. How long have you had this car and when was the last time it ran good? Could be a points issue too.

  6. #5
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help

    A bad timing chain could also contribute to the problem. If yours is original, the plastic
    teeth on the cam sprocket could fail at any time and gernade your engine. Before that,
    it just won't run as well. Bruce Roe

  7. #6
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help

    Sounds like a big vacuum leak somewhere. Maybe the adaptor stuff is not sealed completely.

    One bad spot for clodrajet adaptors is around the secondaries.

  8. #7
    cadillac_81 is offline Cadillac Owners Member
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    What about the cam sprockets on a 368? Are they plastic?

  9. #8
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Car runs good in Park, but shift it into Reverse or Drive and it stalls!!!! Help

    Quote Originally Posted by cadillac_81 View Post
    What about the cam sprockets on a 368? Are they plastic?
    I believe so. Check for slack. Bruce Roe

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