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20 amp Overdrive fuse blows

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  • Electrical: 20 amp Overdrive fuse blows

    Hello all. On my '51 champion 6cyl. the above fuse keeps blowing....apparently when I go to overdrive. Is the O.D. relay or kick down switch bad? Has anyone had this happen on their car? Any input will be much appreciated. Thx, louis m, sacramento ca.

  • #2
    The overdrive solenoid has two coils.
    One pulls the overdrive initially and the second coil is a holding coil.
    If the contacts in the solenoid do not switch over to the holding coil , the current will be high and the fuse will blow.
    The fuse is a time delay special fuse.
    http://www.hemmings.com/hmn/stories/...feature29.html

    Robert Kapteyn

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    • #3
      Check the OD component wiring harness. Unless it has been replaced, the original could have areas where the insulation has come off causing a short circuit. Hope this helps.

      Dan Miller
      Auburn, GA

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      • #4
        Originally posted by rkapteyn View Post
        The overdrive solenoid has two coils.
        One pulls the overdrive initially and the second coil is a holding coil.
        If the contacts in the solenoid do not switch over to the holding coil , the current will be high and the fuse will blow.
        The fuse is a time delay special fuse.
        http://www.hemmings.com/hmn/stories/...feature29.html

        Robert Kapteyn
        I don't want to start an argument here, but enlighten me on the "special time delay fuse."

        I have had my overdrive fuse to blow and have had to take the overdrive relay apart and clean the contacts. I merely replaced the fuse with standard appropriate amp fuses and everything works. To a point...all fuses are somewhat "time delay." What ever time it takes for the metal strip to reach its melting point. That could be milliseconds or something beyond. I am not aware of another "special" requirement or any fuse designated "special" for use with overdrives.

        By the way, the link you posted is an excellent overview of overdrives.
        John Clary
        Greer, SC

        SDC member since 1975

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        • #5
          The shop manual calls for a 20 amp fuse, but doesn't state exact style. If memory serves you need an SFE20 fuse. This is 20 amp, but can withstand a temporary current above that before blowing. A 12 volt system used an SFE14. Circuit protection can be fairly complex. For example a standard 20 amp fuse should blow quickly at 20 amps, but could also blow at a considerably lower value applied continuously. That is in part why fuses are generally rated considerably higher than the actual load.
          American iron, real old school
          With two tone paint, it sure is cool

          Its got 8 cylinders and uses them all
          With an overdrive that just won't stall

          With a 4 barrel carb and dual exhausts
          With 4.23 gears it can really get lost

          Its got safety belts and I ain't scared
          The brakes are good and the tires are fair.

          Tried to sell her, but got no taker
          I"ll just keep driving my Studebaker

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          • #6
            I have had the same problem and with me the culprit was the OD kick down switch shorting out so you really have to go through it one part at a time.
            If you car is ugly then it better be fast.....

            65 2dr sedan
            64 2dr sedan (Pinkie)
            61 V8 Tcab
            63 Tcab 20R powered
            55 Commander Wagon
            54 Champion Wagon
            46 Gibson Model A
            50 JD MC
            45 Agricat
            67 Triumph T100
            66 Bultaco Matadore

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