Speedometer problems 1991 Pete

Discussion in 'Peterbilt Forum' started by john379, Oct 22, 2010.

  1. john379

    john379 Bobtail Member

    Oct 22, 2010
    Louisville, KY
    We have a 1991 Peterbilt with a 460 Cummins engine. The speedometer stopped working. I have checked the sensor on the rear of the transmission and it is sending out a signal. The speedometer head was placed in another truck and it worked. Does anyone have any idea as to why the speedometer just quit working, if so, what do I check next? I hope I don't have to take it to a dealer to be fixed $$$.
  2. puncher

    puncher Medium Load Member

    Feb 12, 2010
    I think the sensor works on ohms,but anyway I would probably do a continuity check to make sure no broken wire or bad connection. This is just what I would do and you may have already done this but good luck none the less.
  3. jaysolomon

    jaysolomon Light Load Member

    Sep 17, 2010
    I have a 2000 379 and the speedometer screwed up in it and I was not about to spend that much for a new one so I went to Best Buy and bought me a GPS with speedometer built in it. It was a lot cheaper than speedometer. I was told all Garmin brands have it in there
  4. bighauler

    bighauler Bobtail Member

    Nov 14, 2010
    you could always get a tel-tek!!
  5. Krooser

    Krooser Road Train Member

    Jul 25, 2010
    Old post... but the sender needs to be adjusted properly...
  6. mtmval

    mtmval Bobtail Member

    Jan 8, 2011
    My 1991 379 w/Cummins 460E has the exact same problem. Replaced the sending unit with no success. Wires have continuity until they appear to go into the engine-mounted computer...haven't checked anything beyond that yet. Please let me know if you find the problem as I am also looking to avoid the dealer $$$.
  7. Priceless 1010

    Priceless 1010 Bobtail Member

    Sep 29, 2011
    burnett wisconsin
    Ive got a 1991 Peterbilt with a detroit and we changed the tire size and transmission but nobody can seem to help me in recalibrating the speedometer. Ive tried the ametek formula but no luck. If anyone has any helpful information that would be greatly appreciated. 285 75 24.5 tires 3.90 rear ends and a 13 speed transmission.
  8. kustom

    kustom Light Load Member

    Aug 11, 2010
    coos bay, oregon
    mtmval, check your speedo for power and ground, then check your signal wire coming from the ecm. If these wires are good, then either of 2 things happened. 1 is the ecm isn't seeing a signal coming from the sensor but you said you changed it. You can verify this works properly by checking if cruise control works. 2 your speedo is bad.
  9. kustom

    kustom Light Load Member

    Aug 11, 2010
    coos bay, oregon
    priceless 1010, do you happen to know if the engine ecm drives the speedo? If it does, then it's easy. Just go into a dealer and have them recalibrate the ppm's in the ecm. If it doesn't, then yes you have to recalibrate the speedo head. Looking at you'r specs, are you figuring in the number of teeth on the chopper wheel that the speed sensor reads into your equation?
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