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Tach reads about double?

Discussion in 'The Hokey Ass Message Board' started by Slantback, Apr 28, 2013.

  1. Slantback
    Joined: Sep 6, 2006
    Posts: 80


    <hr style="color:#D1D1E1; background-color:#D1D1E1" size="1"> I have a MSD 6 series box with a MSD 8563 distributor and MSD 8920 tach adapter. My tach is an old school Stewart Warner Greenline 960 AA. It reads almost double what it should. I can't seem to find any info as to the cause. It's as if it's set up for a 4cyl.
    Any help will be appreciated.

    Thanks, Colt
  2. That would be my guess......
  3. Flatheadguy
    Joined: Dec 2, 2008
    Posts: 2,037


    "About double" would indicate that it is not a 4 or 8 cylinder mismatch. "ALMOST" means just that...almost, nearly, but not exactly. Double check that statement. Keep us updated if you find the problem.
  4. metalshapes
    Joined: Nov 18, 2002
    Posts: 11,009

    Tech Editor

    No, it could...

    Was the RPM checked with another tach, or is the "about double" playing it by ear?

    And if it was checked with another tach, it could be a little off calibration.
    Or the one you are checking is.
    Or they both are, one up and one down, for example...

    BTW, I/m guessing we are talking about electronic tach's, right?

    Because mechanical tachs come in 1/2 RPM and 1/4 RPM...

  5. Slantback
    Joined: Sep 6, 2006
    Posts: 80


    All I have to verify RPM is and old dwell tach, red to - on coil / black to ground. Works fine on my old bug, get nothing on my 37. I will admit to being a dumbass on this stuff but I don't see any switch or adjustment on this tach.
  6. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,453

    Dan Timberlake

    Did the SW tach read correctly before the MSD was installed. ?

    Google didn't find much for a 960 AA, but seems like some other SWs have a switch for the number of cylinders.
    I had one or 2 old lesser ones that I had to snip a resistor or something out of an internal circuit to set it for the right number of cylinders
  7. Pops1532
    Joined: Jun 19, 2011
    Posts: 544

    from Illinois

    Some electronic tachs have wires that you clip for 6 cyl and 4 cyl.
  8. SloppyEggs
    Joined: Jan 10, 2012
    Posts: 197


    I second that
  9. blacksheep55
    Joined: Jan 26, 2011
    Posts: 84

    from jasper ga

    Am I incorrect that some of the old tachs will not operate on an electronic ignition, even with the tach adapter? I have an old Sun that I wanted to use in my car but if I remember correctly it needed to be sent out to Tachman or the likes to be converted. But I did used to smoke alot of weed when I was a kid, so maybe I'm imagining things.
  10. 55 gasser pickup
    Joined: Dec 17, 2010
    Posts: 479

    55 gasser pickup
    from utah

    I'm having the same problem with mine.(reads 4000 rpm at 60 mph)My tach is a new one from moomeyes.half sweep style.I have h.e.I.. in an off topic elcamino (66).its a three speed on the tree with 373 way its turning that.
  11. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    from florida

    Some tachs have a 4-6-8 adjuster screw on the back and some you use certain wires. IMO right now you are on the 4 cylinder setting.

    As for the new SW tach not reading right, I have the same tach except the full sweep version, with electron ignition, and it reads right. Call SW and run it by them. Even with 4.30 gears I only turn 3,000 at 60, so yours is way off.

  12. Cerberus
    Joined: May 24, 2010
    Posts: 1,392


    I have several tachs: SW, Autometer, Sun, etc. Most have a dial on the back with a slot that requires a flat tip screw driver to set the tach at 4, 6, 8, cyl. These settings allow for an accurate rpm reading.
  13. Is the old tachometer 6 volts?
  14. 55 gasser pickup
    Joined: Dec 17, 2010
    Posts: 479

    55 gasser pickup
    from utah

    I don't mean to hyjack anybody thread.
  15. Willy301
    Joined: Nov 16, 2007
    Posts: 1,426


    You might look over the MSD, the MSD box senses the rpm from the distributor, and may not be sending a signal that is compatible with the tach.
  16. Slantback
    Joined: Sep 6, 2006
    Posts: 80


    :) Well the mystery is solved. After pulling the dash apart and removing the tach, I found no switch, wires, or access to the internals. After carefully removing the bezel and lense and pulling the guts out, there it was! A small dial that could be adjusted using a small screwdriver. very hard to make out any numbers but I think it has A 4, 6 and 8 on the dial. played with the adjustments and it's working now. I know these old electric tachs are kind of lazy and not extremely accurate but it seems to be pretty close. Here is my combo;
    MSD distributor #8563
    MSD coil #8202
    MSD tach adapter #8920
    S/W tach #960-AA (no sender required)

    Sorry about the pic quality but its the best I could do.


    Attached Files:

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