C-3 1975 tach problem - NCRS Discussion Boards

C-3 1975 tach problem

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  • KEN BUTCHER
    #1

    C-3 1975 tach problem

    Well gang, I finally got my steering column down and also the tach out and replaced the left speaker. Now I'm trying to figure out why the tach doesn't work properly(it's slow)(when engine revs at 3,000rpm tach shows 1,400rpm) It has a ECKLER'S print board and it looks fine, but what do I know I'm no electronic wiz. Anybody have any info, suggestions, experience, help. I hate to just spend $ on a new print board and have the same problem.
    Thanks my brothers.
    Ken.
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    • Joe L.
      Beyond Control Poster
      • February 1, 1988
      • 43193
      #2
      Re: C-3 1975 tach problem

      Ken-----

      The most often-occurring tach problem for electronic tach Corvettes is the tach filter. This unit is mounted on the intake manifold, as I recall. Often times, one of the wires will "break off". If this turns out to be your problem, I believe that reproductions of this piece are now available. They were not so-available for years after GM discontinued the part.
      In Appreciation of John Hinckley
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        • KEN BUTCHER
          #3
          Re: C-3 1975 tach problem

          Hi Joe, I disconnected the tach filter and ran the tach wire straight to the distributor and there was no difference in RPM movement, would using or not using the filter make a difference on a vehicle with a properly functioning tach. I'm stooped!!!!!. The filter wire was pretty weak and it did break off, so I soldered it on and how do you know what the ohm reading is suposed to be on a tach filter to see if it's defective or not.
          Thanks.
          Ken.
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            • Joe L.
              Beyond Control Poster
              • February 1, 1988
              • 43193
              #4
              Re: C-3 1975 tach problem

              Ken-----

              The tach filter is not an "optional" thing as far as tach operation goes. It has to be in the circuit for the tach to work properly. If the wire broke off so easily, I'd say that was likely the problem. I don't know the resistance value. However, I do know that if the wire breaks off right at the "condensor" (as it often does) it's very hard, if not impossible, to repair properly.
              In Appreciation of John Hinckley
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                • KEN BUTCHER
                  #5
                  Thanks Joe, good help is hard to find! *NM*

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                    • KEN BUTCHER
                      #6
                      Re: Thanks Joe, good help is hard to find!

                      But of coarse the NCRS has lots of good helpers out there with endless amounts of information. Thanks.
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