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Tachometer works, tranny works. Tach doesn't work, tranny slips bad

Discussion in '6.9L IH & 7.3L IDI Diesels' started by dan-o, Jul 1, 2020.

  1. dan-o

    dan-o Registered User

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    My 1989 ambulance is acting weird. Started up great today, but the tach was reading 0. I put it in reverse. No problem backing up. Put it in drive and it acted like it was VERY low on transmission fluid. Dip stick showed it a little low after letting it warm up, so I adding 1/2 qt. Still the same problem. I drove it around the driveway anyway. Then the tach started working and the torque converter engaged and it worked fine the rest of the day.
    I checked the tach sensor resistance. It checked out.

    Any of you guys ever see this before?
     
  2. ih8minimumwage

    ih8minimumwage Full Access Member

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    Your transmission reads from the tach sender. If the sender ohms out okay, you can pull it and clean the end off. It's a standard mag pickup that operates off of the gear teeth, and can collect all the microscopic metal in the oil and stop reading correctly.
     
    DaveBen and Danielle like this.
  3. dan-o

    dan-o Registered User

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    Thank you SO much!
     

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