muncie speedo bullet and adapter 1970 Z28

Discussion in 'Transmission & Driveline Topics' started by Jeffmort, Mar 22, 2017.

  1. Jeffmort

    Jeffmort Veteran Member Gold Member

    436
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    Jan 7, 2004
    Encinitas, CA USA
    Question:
    My "new to me" 1970 Z28 had an adapter fitted onto the speedometer gear bullet - I understand this is likely original to this car.
    My question is: why cant I simply thread my speedometer cable directly to the "bullet" and not use the adapter part? The threads for on the bullet seem to match the threads on the speedo gear.
    If I must use the adapter I will - I am mostly curious why the adapter is needed.
    See picture:
    speedo.JPG
     
  2. JodysTrans

    JodysTrans Veteran Member

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    Feb 9, 2006
    Reading, PA
    Since your '70 Z has a 764 or the 584 tail extension, only the 8 tooth speedo drive gear was available back in the day for the Chevrolet's. The ratio adapter was used to properly calibrate your speedometer/odometer. You can eliminate the adapter, but your speedometer will be off.

    Today we have 7, 8, and 9 tooth speedo drive gears to eliminate these ratio adapters.
     
  3. Twisted_Metal

    Twisted_Metal Moderator Staff Member Lifetime Gold Member

    25,754
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    Feb 26, 2004
    Bloomington, MN
    The adapter is also a ratio modifier to get the speedometer to read accurately.
    If you look closely... There's probably a number on it specifying the ratio of the adapter.
     
  4. zachary8

    zachary8 Veteran Member

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    Jan 22, 2012
    Chicago, Illinois
    The speedo reading on my 70 Z is off. (Not the biggest problem in the world but it annoys me) I did a quick search on ebay and did not find any listings for an item like this. Could somebody please tell where they are available for sale. Thanks, Lou
     
  5. Twisted_Metal

    Twisted_Metal Moderator Staff Member Lifetime Gold Member

    25,754
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    Feb 26, 2004
    Bloomington, MN
    Zach... How far is it off? (@ 60 MPH)
     
  6. budro6968

    budro6968 Veteran Member

    2,174
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    Apr 2, 2016
    Jax Florida
    My 78 Z had that too. It had a two piece speedo cable. It never worked because the cable dropped down on the ground somehow and about ground it in half before I owned the car. I never fixed it. Drove with no speedo for 11 Yrs. My 81 Z with T-10 has the speedo hole on the pass side. The cable does not reach at this point. I think that it needs that same set up to work. I can't remember if the 78 was on the same side.
     
  7. zachary8

    zachary8 Veteran Member

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    Jan 22, 2012
    Chicago, Illinois
    I have estimated that it's about 25% off. (slow)
     
  8. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Oct 3, 1999
    Beavercreek, Ohio, USA
    My 70z with 3.73's did not have one of these, but I seem to see them more on the 4.10 equipped cars.
     
  9. COPO

    COPO Veteran Member Lifetime Gold Member

    16,333
    261
    Sep 15, 1999
    Ontario, Canada
    70 Z28 speedo color s/b
    [​IMG]

    [​IMG]
     
  10. 70lt1z28

    70lt1z28 Veteran Member Gold Member

    1,969
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    Oct 3, 1999
    Beavercreek, Ohio, USA
    So are z28's supposed to have one or not?
     

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