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Thread: Possible transmission issue?

  1. #1
    Junior Member
    Join Date:  Nov 2014

    Posts:    3

    Possible transmission issue?

    I have an AUG 81 automatic DMC. I was driving on the highway at about 75 mph when my engine began to sound like it was revving, but the car was losing speed. I pulled over and stopped to figure things out. Once stopped, I was unable to get the car in a gear. After an hour or so, I was able to get the car to move forward slowly in drive with my foot off of the gas pedal, however, when I pressed the gas pedal, the engine would just rev, but the car would not accelerate. I had the car towed to the house. When I got it to the house, I tried driving it again to see if the issue still existed. I was able to drive the car up to about 20 mph, but when I would try to accelerate up a hill I would encounter the same issue with the car not accelerating. The next morning I ended up testing things out and I was able to drive the car around the neighborhood without issues. I have not driven since, which has been about a week.

    Where do I start to figure out the issue?

    Thanks in advance.

    VIN 3344


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  2. #2
    Concise Member Jonathan's Avatar
    Join Date:  Jun 2011

    Posts:    3,739

    Where to start looking?

    1.) Check the ATF level. With the car parked on level ground, start it and get the engine hot enough to kick your cooling fans on and off. With your foot on the brake, put the shifter through all the gear positions, then check the level on the dipstick while parked and engine on. Add fluid if it's low.

    2.) Drain the ATF and remove the pan. Inspect the filter to see if it is dirty and plugged. Your trans will do what you described if you're starving it of fluid. Replace filter with a new one from Michael M./DMCH and refill fluid to proper level.

    3.) Inspect shift computer wiring harness to see if it has been damaged by lying on top of the exhaust cross over pipe. If the wiring looks ok from outside, it is probably the components inside the control box that need to be rebuilt.

    If it isn't fluid related than it is likely the shift computer governor. Those together would represent about 95% of the problems people have with the auto trans.

    EDIT: Test drive the car of course after completing the 1st step before moving on to the 2nd or 3rd steps.
    Last edited by Jonathan; 03-05-2017 at 09:21 AM.
    One damn minute Admiral...


  3. #3
    Junior Member
    Join Date:  Nov 2014

    Posts:    3

    Quote Originally Posted by Jonathan View Post
    Where to start looking?

    1.) Check the ATF level. With the car parked on level ground, start it and get the engine hot enough to kick your cooling fans on and off. With your foot on the brake, put the shifter through all the gear positions, then check the level on the dipstick while parked and engine on. Add fluid if it's low.

    2.) Drain the ATF and remove the pan. Inspect the filter to see if it is dirty and plugged. Your trans will do what you described if you're starving it of fluid. Replace filter with a new one from Michael M./DMCH and refill fluid to proper level.

    3.) Inspect shift computer wiring harness to see if it has been damaged by lying on top of the exhaust cross over pipe. If the wiring looks ok from outside, it is probably the components inside the control box that need to be rebuilt.

    If it isn't fluid related than it is likely the shift computer governor. Those together would represent about 95% of the problems people have with the auto trans.

    EDIT: Test drive the car of course after completing the 1st step before moving on to the 2nd or 3rd steps.
    Thanks, I will give it a try!


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  4. #4
    Not really banned Michael's Avatar
    Join Date:  May 2011

    Posts:    2,780

    Trans is definately slipping. A full service like Johnathan outlined. I was out of filter kits for a few months but just got a batch of new gaskets in and my magnets should be here soon. The vendors still should have some transmission kits though.

    Hopefully the clutches didn't get damaged. If a fluid/filter service does remedy the problem you may want to drain and refill the fluid after a few months because there is probably a lot of clutch material in there that needs to be flushed out.

  5. #5
    Senior Member
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    Location:  West Sayville, N.Y.

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    Slipping transmission

    You won't like what I'm about to say but it sounds like the transmission has a cracked drum which will cause exactly the symptoms you describe. Low fluid will cause slipping when the transmission is cold which will lessen or go away as the A.T. warms up. A cracked (hairline at this early stage) drum will cause slipping as the unit warms up. I've never seen a bad computer cause slipping but it will overstress the A.T. and lead to a cracked drum later. My guess is you or a PO replaced the computer governor previously but did not do it soon enough to avoid stressing the unit leading to the failure you are experiencing now. I've personally seen this scenario unfold over 75 times over the years so I'm speaking from my past experience. For your sake I hope I'm wrong. If I'm right we can offer you the best deal on a new transmission by replacing only the automatic section and reusing the differential which rarely fails. You could send the transaxle to us and I would personally fit the new auto unit to the differential and set the clearances and clean up the B2 drum edges which are too sharp (sharp edges are stress risers on shift drums) from the factory and are another reason for failure. It is pointless to rebuild the unit with one new drum as the other drum will have also been stressed and may subsequently fail unless you replace both. It is more cost effective and safer to replace the complete auto housing with all internal parts. Again I hope I'm wrong but the odds are against it.
    Rob

  6. #6
    Delorean Guru
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    Even if you don't have a cracked drum, from your driving and testing you probably ruined one of the clutch pack's friction plates. Pull the dipstick and smell it. If the fluid smells burnt and/or is gritty and dark, you just bought yourself another transmission. While your old one may be rebuildable, PJ Grady's option may be the best way to go. Once you drive the auto trans and notice it is slipping you are done. One of the clutches is so small, any slippage is enough to finish it off.
    As part of your owner maintenance checks which you should do once a month on ANY car you drive, you should be checking:
    1) glass for cracks and chips
    2) lights for operation and burnt out bulbs
    3) tires for pressure, wear, and defects
    4) controls for operation
    5) motor oil for level and change interval
    6) wiper blades
    7) auto trans fluid level and condition
    Think of it like a pre-flight check before you drive the car. On aircraft it is done before EVERY flight.
    David Teitelbaum

  7. #7
    Junior Member
    Join Date:  Nov 2014

    Posts:    3

    Quote Originally Posted by David T View Post
    Even if you don't have a cracked drum, from your driving and testing you probably ruined one of the clutch pack's friction plates. Pull the dipstick and smell it. If the fluid smells burnt and/or is gritty and dark, you just bought yourself another transmission. While your old one may be rebuildable, PJ Grady's option may be the best way to go. Once you drive the auto trans and notice it is slipping you are done. One of the clutches is so small, any slippage is enough to finish it off.
    As part of your owner maintenance checks which you should do once a month on ANY car you drive, you should be checking:
    1) glass for cracks and chips
    2) lights for operation and burnt out bulbs
    3) tires for pressure, wear, and defects
    4) controls for operation
    5) motor oil for level and change interval
    6) wiper blades
    7) auto trans fluid level and condition
    Think of it like a pre-flight check before you drive the car. On aircraft it is done before EVERY flight.
    As a pilot myself, that makes sense. It didn't help with the issue I am having, but the logic is correct.


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