240 Speedo signal in GT

So it's been spoken about a bit but I'm not finding a solution other than "fit a later dash and speedo" which I don't want to do. 1980 242GT running a b23ET with LH2.4 transplant. Car runs great however it's just plain antisocial albeit fun watching in the rear view as terrified pedestrians jump into the bushes in fear whenever I back off due to the lack of a speed sensor in the diff and the accompanying signal to the speedo and wiring from that to the ecu causing SNAP, CRACKLE and POP.

I've got a later diff to go in to provide the signal and have a later speedo too but want to retain the rsport cluster so wondered if there was a work around anyone knew of?


  • edited August 6

    The '87-spec cluster with the electronic speedo causes some sort of minor short when installed in the '81 dash that's in my GT … so having gone to all the trouble of getting rid of the drive-cable by putting a sensor on the gearbox itself, I went looking for a way to use my '81 cluster with mechanical speedo along with the sensor on the 'box.

    The only thing I could find, and I don't know if it's noisy or not, was a motor to attach to your speedo, and which varies speed with the frequency of the input signal. They weren't cheap either, I can't remember but I've got something in the order of ~$400 in mind, and then you had to work-out how to install it.

    It might be more reasonable to see if you can find an instrument specialist who can swap a new generic mechanism into your R-Sport speedo? Actually it was an instrument specialist who said the aforementioned drive-motor exists, so you might need to get in touch with one anyway … I'd hope you can find something closer to home, but if not, it was these guys not that far from me: https://www.manlyautoinstrumentrepairs.com/ (coupla years ago now). Thinking on it further, might be worth pulling the speedo out & seeing whether the mechanicals will separate from the dial itself - can't see why it couldn't be a DIY job, assuming the replacement mechanism is configurable/adjustable ...

  • The thought that comes to my mind is disassemble the electronic speedo to minimum number of components and put it in a case out of sight somewhere.

  • ^ Interesting thought … is the clock used, could the clock be replaced with a digital speed display, maybe?

  • DauntlessDauntless (@Dauntless) Central West NSW
    edited August 6

    The original speedo cable will be driven from the gearbox, so surely it would be possible to fit a diff with speedo tone wheel and wire this to the ECU only? If some electronics from the speedo are required to achieve this, it would be worth doing as @VolvoHordz suggested.

  • edited August 6

    Eff me … I totally misread the original post didn't I? For some reason I read that it had the diff sensor installed & it had no speedo. 😣

    My bad … yes, as Dauntless & VolvoHordz said, if you've currently got a speedo then installing the diff will get the signal to the ECU without needing to touch anything else.

    Move along, nothing to see here …

  • volvodrivermanvolvodriverman (@volvodriverman) Barringwood Estate, Tasmania

    This is was where I was at failing a simpler solution but it looks like the go. Cheers.

  • RobRob (@Rob) - Lockyer Valley, SE Qld

    Pretty much exactly what I have done in my Amazon in order to run Lh2.4

    I stripped down the electronic speedo, removing all components not required, installed a resister in place of the speedo output and mounted it all in a plastic box that is mounted up under the dash.

  • volvodrivermanvolvodriverman (@volvodriverman) Barringwood Estate, Tasmania

    Awesome! Would you mind outlining the specifics of what you kept and the resistor spec?

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