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    Author Topic: How to test if tach is broken?  (Read 2577 times)

    Offline andben

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    How to test if tach is broken?
    « on: July 27, 2014 - 04:13:57 AM »
    I got a 71 cuda with Rallye Dash. I need to test my tach if it's broken. (I have a MSD box installed so tach is not working due to that). So I installed a MSD 8920 tach adapter but the tach is not moving at all.

    So how to test my stock tach?

     :worshippy
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    Offline dfrazz

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    Re: How to test if tach is broken?
    « Reply #1 on: July 27, 2014 - 10:03:43 AM »
    What kind of a MSD box?  The 6AL has a tach connector, just connect your tach to it.

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    Offline andben

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    Re: How to test if tach is broken?
    « Reply #2 on: July 29, 2014 - 06:27:35 AM »
    Quote from: dfrazz on July 27, 2014 - 10:03:43 AM
    What kind of a MSD box?  The 6AL has a tach connector, just connect your tach to it.

    It's an old MSD 6A. Never heard about a stock tach working with an MSD box?!

    I therefore purchased a MSD 8920 Tach Adapter but tach is not moving. Probably broken?

    How to test tach if working or not?
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    Offline MEK-Dangerfield

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    Re: How to test if tach is broken?
    « Reply #3 on: July 29, 2014 - 04:16:33 PM »
    Quote from: andben on July 29, 2014 - 06:27:35 AM

    How to test tach if working or not?

    If it's still installed in the car, then you have the added variables of a broken wire, or a bad connection someplace.

    If it's out of the car, you need a power supply and a signal generator with variable frequency to bench test it.

    For what it's worth, it's common for these old tachometers to need rebuilt.
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    Mike

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    Offline dfrazz

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    Re: How to test if tach is broken?
    « Reply #4 on: July 29, 2014 - 05:50:10 PM »
    Quote from: andben on July 29, 2014 - 06:27:35 AM
    It's an old MSD 6A. Never heard about a stock tach working with an MSD box?!

    I therefore purchased a MSD 8920 Tach Adapter but tach is not moving. Probably broken?

    How to test tach if working or not?


    Does your box wiring look like this?  There should be a tach output location or wire you connect directly to your tach.
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    Offline andben

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    Re: How to test if tach is broken?
    « Reply #5 on: July 30, 2014 - 03:29:49 AM »
    Tach output is GREY, I have that. But its NOT working with STOCK tach, only with aftermarket tachs thats made to work with msd box.

    MSD 8920 is an adapter that connects to the grey output wire and "converts" the signal to work with stock tachs but my tach is not moving.

    Need to pull tach and benchtest it.
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    Offline Bullitt-

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    Re: How to test if tach is broken?
    « Reply #6 on: July 30, 2014 - 07:52:16 AM »
    I thought the tach would work with an MSD just would not read correctly...

    As for bench testing, other than using a signal generator, I ran across several references to using a battery charger.
    Never tried it myself & could only find one good explanation on the www.  I believe ours is the RVC type
    http://www.mgb-stuff.org.uk/tachtest.htm
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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    Offline joelson6

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    Re: How to test if tach is broken?
    « Reply #7 on: August 01, 2014 - 11:29:29 AM »
    IMHO, sounds like your tach is dead.
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