Apparently some of the 1986 and newer Volvo 240 with electronic speedos read high or low vs GPS speed, and they can be recalibrated to read correctly. Mine reads about 10kmh high.

A few guides say to replace a resistor on the speedo PCB. Here's one https://turbobricks.com/index.php?threads/240-electronic-speedometer-calibration-1986.239021/

It quotes the stock resistor being about 56 ohm.

Below is a pic of the one from my car, the colour bands don't seem consistent with current resistor colour band coding?

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Banding looks like blue/teal, brown, brown, gold, brown. Online calculator puts it at 61 ohm.

Anyone able to confirm or correct the ohm rating of the circled resistor?

Yes 240 speedos do read roughly that much faster.

they thought it would keep the drivers safer and prevent speeding tickets

See the calibration article on www.cleanflametrap.com

Before I nicked off to go cruisin', I was faffing round with a VN Commodore electronic speedo, which are also VDO designs and not unlike the 240/700/ 900 designs.
I used one of these gadgets to simulate the speed signal.

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If I get a bit of spare time over this weekend, I might try setting up a 240, an LH 2.2 740, and an LH2.4 940 speedo to it and seeing what readings I get.

This is what I got with the VN speedo:

  • set to sine wave
    83 Hz = 60 km/h
    120 Hz = just under 90 km/h
    150 Hz = just over 110
    180 Hz = 135 km/h
    200 Hz = 150 km/h
    280 Hz = 205 km/h

Volvo speedo frequencies and speeds to be added.....

Well I came across a post on Iroll where a member had wired in a trim pot in place of the resistor, to allow for more calibration possibilities.

Thought I'd give it a go myself.Image description

Unfortunately I didn't take progress pics, as I was doubtful I was going to succeed. ( A previous attempt to desolder a component from a PCB and solder on a new one did not go well at all) My luck must have been better this time.

After playing around with the trim pot, id say the Speedo is about 98% accurate, it seems to be spot on at a particular speed then slightly off at other speeds, though it's much better than before.

Worth a go if the speedometer on your 240 is significantly out like mine was.

    a month later

    I have the same issue. I need to be doing 112km/h on the clock to get 100km/h on GPS.

    I also think this throws off the odometer as it also reads higher?

    1989 240 wagon.

    So the trim pot replaces the circled resister in the first picture?

      The odometer and trip meter are separately calibrated to the speed.

      as long as you know your tyre size is correct, you can gauge the trip meter accuracy in two ways, drive down the highway and count the mile markers or use GPS to track distance

      I prefer the former

      When these 240s were new, the trip and odometer were accurate but even when new the speedo reads about 5-10% fast, a trick by Volvo to sneakily get people to slow down

      morch_66479

      Based on my rough observations by looking at roadside markers., the odometer was counting fairly bang on.

      I could not figure out the resistance of the original speedo resistor, hence I put in the trimpot to allow for adjustment. I got mine from Jaycar and followed the instructions in the turbobricks link in the opening post of this thread.

        Mine has bigger sized rims - the 15 inch steelies from the 740 model

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        It’s not so much the size of the wheels, but the tyres profile.

        Meaning the height of the tyre. Top to bottom

        This distance directly alters the revolutions per kilometre (a taller tyre rotates fewer times in a kilometre than a shorter one)

        If 15” wheels are being used then the equivalent to 195-75-14 (which is the factory fitted size on a 240 wagon) is 205-65-15

        I had no choice but to calibrate ‘cos I used a Toyota gearbox sensor with the 240 non-gearbox-cable speedo (which was easier than fitting whatever diff components I needed for the diff with the speedo pickup), so I bought one of those Jaycar adapter-box kit thingies. It does get confused on occasion, maybe once a year the speedo stops working for no apparent reason, but “have you tried turning it off and on” fixes it … seems to work pretty well otherwise.
        Of course my speedo calibration could be a bit bodgy, based as it was on ‘phone GPS readings … 🙂

        The proportion by which the OEM speedo’s reading high is pretty standard across most makes & models, Volvo’s certainly not alone in designing it that way.

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