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Speedo reading "bouncing" about??

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    Speedo reading "bouncing" about??

    Hi all,
    I guess this may well have been a topic previously covered, but here goes anyway. Bought my Stag late last year and have only driven it twice, but have been and will continue sorting out it's various issues as i come across them - which brings me back to my speedo. As stated it doesn't sit at any given speed it "bounces" around. Could anyone please point me in the right direction for the usual causes/fixes of this problem, hopefully i'll then get to the bottom of it and get the issue resolved.
    Cheers
    Gord

    #2
    I'm not sure of any Stag specifics but in tthes old cars, the Speedo is driven by a cable which is like a spring centre. If this gets tight (lack of lubrication or a kink for example), then it winds up and then releases over and over, giving you a bouncy needle.

    I'd check the cable for lubrication first. Equally, it could be a stiff disc in the Speedo itself as the cable drives a disc which attracts the magnet attached to the needle. Something like that anyway. Far too long since I've messed with Speedos like this.

    Hopefully someone else may know of Stag specifics but for what it's worth, mine fluctuates a bit at lower speeds, it doesn't bother me though. I know what 30mph equates to in V8 stentorian baritones which is a far more useful unit of measure

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      #3
      Speedo cable dry or badly run would be the first thing to look at, but you probably have a 45-year-old speedo which was never very steady from the start. Unlike modern cars, our speedometers are fairly crude affairs which rely on magnets, discs, and hairsprings. If lubricating (sparingly) the cable doesn’t sort it you could either live with it, send it away to get it overhauled, or buy the electronic one that is advertised for sale on here.
      Dave
      1974 Mk2, ZF Auto, 3.45 Diff, Datsun Driveshafts. Stag owner/maintainer since 1989.

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        #4
        Had the same fault on my brothers car 2 weeks ago,he had the speedo overhaulled by speedy cables,(there not quick) as we replaced the speedo we also replaced every thing cable, gear in gearbox and new angle drive, the cable from LD parts is shorter than from other places

        Dave
        73 mk 1/2 now gone to the dark side BLUE

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          #5
          Replaced the inner cable on mine a few times - still got a speedo reading of 70 +- 30 mph !! Finally replaced complete cable - steady as a rock.
          '72 Manual O/d Saffron Yellow

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            #6
            Afternoon to Gord et al,

            Ye olde "they all do that sir" can (somewhat) be applied here !
            My '77 car does this too, but ONLY at low (i.e. less than 15mph indicated) speeds.
            Anything above that and it's pretty steady with only very small variations.
            It does also make "noises" at very low speeds, a kind of low-volume rotational noise.
            Indicated mileage is just 34k, so possibly wear/age could still be factors.
            I remember back in '78 my '74 Dolomite Sprint did exactly the same, but indicated speed did really "bounce" up/down by about 10 mph.
            Wonder if it's possible the speedo drive end of the cable might be worn ?
            No doubt others with more knowledge than I will be able to advise:- looks like plenty of suggestions already!
            Best of luck with this,

            Neil.

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              #7
              New cable and make sure it runs in a smooth curve everywhere

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                #8
                Thanks to all who have responded. Looks like i'll check/replace the cable as a first port of call then go a bit more in depth if needed.
                Cheers
                Gord

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                  #9
                  Yup, like others say, 1st thing is to fit a new cable. Sorts it out most of the time.
                  Auto transmission rebuilding since 1979 - for my sins!

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                    #10
                    I'd assumed this was normal! Mine is steady at higher speeds, but around 30 it tends to bounce around between 27-33. I just work on the assumption that an average of the two is my actual speed... that's what I'd be telling the fuzz anyway!

                    Comment


                      #11
                      Originally posted by Scar View Post
                      ... that's what I'd be telling the fuzz anyway!
                      I still maintain that you'd be better off telling them that you were only doing <insert value> burbles per second. It would be worth it to see the perplexed look.

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