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Vacuum Modulator replacement

Discussion in 'Automatic Transmission' started by Ken Beck, Aug 15, 2019 at 8:49 PM.

  1. Ken Beck

    Ken Beck Junior Member

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    Truck Year:
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    I had a nice surprise when I replaced my vacuum modulator (TH350) a couple of days ago due to late shifts........I dumped a couple of quarts of ATF on my driveway and myself.
    I can only assume I have a stuck modulator valve. Can anyone second that motion? Never had to replace one but read on older threads that there is a fix by very lightly sanding it and re-installing?
    PLEASE don't ask me to rebuild the tranny as at this point my license plate should read "MNY PIT" as my wife says.
     
  2. Frankenchevy

    Frankenchevy . Supporting Member

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    just buy a new one, they're super cheap.

    out of curiousity, is your driveway a steep incline/decline?
     
  3. Ken Beck

    Ken Beck Junior Member

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    The point was no ATF should have come out. Slight decline.
     
  4. Matt69olds

    Matt69olds Full Access Member

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    Fluid can leak out the modulator bore. But unless it was overfilled, or you had the front of the truck on car stands, it shouldn’t be very much.

    The modulator is about 20 bucks at Autozone. The part they sell is adjustable, you can raise or lower shift points a couple mph by turning the screw inside the vacuum nipple.
     
  5. Ken Beck

    Ken Beck Junior Member

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    GMC C15
    Engine Size:
    350
    I was replacing the modulator ($12 adjustable from Jeg's) when the leak took place. It may have been 1/2 quart overfull but not enough to leak that much. Now that that is over with, I still have the late shift issue. Changing fluid and filter this weekend.
     
    Last edited: Aug 16, 2019 at 9:07 AM

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