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Thread: TR250/early TR6 v. late TR6 Different Speedo Ratio

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    Yoda glemon's Avatar
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    TR250/early TR6 v. late TR6 Different Speedo Ratio

    I have done a little research but not conclusive, I have an J type (later type) overdrive on my TR250, the speedo reads low, like about 30 mph when I am doing 40 mph. Did the later TR6s have a different speedo ratio drive, if so maybe I can just take the working guts from a late 6 speedo and stuff in mine to make it work right?

    I have looked at my parts manuals and books and the best I can figure out as an answer to the different ratio question is maybe, I see the speedo drive gear in the tranny/overdrive switched at some point.

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    Yoda Gliderman8's Avatar
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    Re: TR250/early TR6 v. late TR6 Different Speedo Ratio

    It might be easier to get a speed ratio adaptor... that's what I did after I installed a Toyota 5-speed. The male end of the adaptor attaches to the transmission, and the speedo cable attaches from the female end to the back of the speedo.
    I paid about $80 locally for the adaptor.
    Elliot
    Central PA
    1973 TR6 Damson Plum / Biscuit interior, HVDA 5-speed, Good Parts Hubs
    1976 TR6 White/Biscuit interior SOLD
    Nostalgia isn't what it used to be.

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    Great Pumpkin TR3driver's Avatar
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    Re: TR250/early TR6 v. late TR6 Different Speedo Ratio

    Quote Originally Posted by glemon
    Did the later TR6s have a different speedo ratio drive, if so maybe I can just take the working guts from a late 6 speedo and stuff in mine to make it work right?
    Definitely different. Earlier TRs always used a speedo drive ratio of 5:2, and changed the calibration of the speedo head to account for changes in tire size, final drive ratio, etc. So the typical calibration for a US-spec TR6 (with 3.7 final drive) was around 1120 turns per mile.

    But the later cars always used 1000 turns per mile, and changed the drive gears to accommodate tires & final drive ratio.

    The speedo drive gears can be changed, but you'll probably have to remove and disassemble the OD to do so.

    A ratio adapter is a good solution, if your speedo works well otherwise; or for about the same money, places like West Valley Instruments can repair and recalibrate your speedo to match your car.
    Randall
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    Luke Skywalker sail's Avatar
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    Re: TR250/early TR6 v. late TR6 Different Speedo Ratio

    Whadda ya mean 80 officer. My speedometer said 60, honest.
    Richard
    65 tr4a

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    Yoda glemon's Avatar
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    Re: TR250/early TR6 v. late TR6 Different Speedo Ratio

    Thanks, I have been looking at ratio adapters, will probably go that route.

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