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What speedo Drive Gear for a 4.11 Diff?

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Eskie92
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2022/05/02 22:16:04 (permalink)
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What speedo Drive Gear for a 4.11 Diff?

Hello Everyone,
 
I have a Type E gearbox which I'm of the understanding was in the Late MK1 Escorts and MK2 Escorts (1973-1980) and were all identical regardless of what model they were in and the only difference being was the speedo drive gear which was dependant on what diff was in the car. 
 
I've accessed the current speedo drive gear and its a 24 tooth gear meaning from my understanding the gearbox was from a late MK2 1600 with a 3.77 diff.
 
I currently have a early MK2 3.89 diff installed and I'm wanting to change it for the original late mk1 van 4.11 diff. My speedo is currently 10km/h out with the 3.89 diff.
 
My question is what speedo drive gear do I need for a 4.11 diff ratio that would make the speedo accurate? I'm also interested in knowing what speedo drive gear would be needed for the 3.89.
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    martymexico
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    Re: What speedo Drive Gear for a 4.11 Diff? 2022/05/03 08:39:03 (permalink)
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    You'll need one with more teeth, a 27t might get it close , if they exist still or you have some laying about to try
    post edited by martymexico - 2022/05/03 13:19:19
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    Eskie92
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    Re: What speedo Drive Gear for a 4.11 Diff? 2022/05/03 15:10:29 (permalink)
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    From what I've been able to find there seems to be 22T, 23T, 24T & 25T drive gears There's 6T and 7T worm gears. I currently have a 7T worm gear. How would the speedo change if I changed to a 6T worm gear? I'm hoping there's some info on what worm/drive gear combo a late mk1 would have had originally with a 4.11 Borg Warner diff.

    Also can anyone tell me if the speedo gears are interchangeable between type 9 and type e gearboxes.
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    martymexico
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    Re: What speedo Drive Gear for a 4.11 Diff? 2022/05/03 17:45:17 (permalink)
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    Type 9 and E do interchange, I did this on my box but also found the speedo was still out so I reset the needle to about -10kmh !
    If you change the worm gear to 6ti believe that will slow the drive gear down at the given speed .. It's one of those try and see things. Failing all that, take the speedo to Auto Instruments they can adjust bob weights / magnets etc to read accurater
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    Eskie92
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    Re: What speedo Drive Gear for a 4.11 Diff? 2022/05/03 23:30:25 (permalink)
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    So I've found this site that I've found useful. Might be of use to others


    https://www.tciauto.com/speedometer-gear-calculator
     
    Just a few calculations I did to test out the site. It all seems to add up as it should
     
    Original Late MK1 Van:
    - 155/80R12 tires
    - 4.11 diff
    - 6T worm gear
    - 23T drive gear
     
    Original Late MK2 1600:
    - 155/80R13 tires
    - 3.77 diff
    - 7T worm gear
    - 24T drive gear
     
    My Current Setup (10km/h inaccurate):
    - 155/80R12 tires
    - 3.89 diff (Early MK2)
    - 7T worm gear
    - 24T drive gear
    *I might be able to use a 25T drive gear to make my current setup more accurate*
    #5
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