Speedo Woes


  1. I bought a 120mph speedo on ebay about a year ago. It sort of worked for a short time but was very optimistic with the speed – speedo showed about 70 when I was doing 40! The mileometer was similarly inaccurate

    I confirmed from the Parnell book that the speedo was the correct one for the final drive (3.44)

    I presumed that the inaccuracy was due to the incorrect speedo drive being fitted to the box, but that proved not to be the case when I had the engine rebuilt.

    The speedo has stopped working completely now. It looks like someone has used the guts from a 90MPH one and put a 120mph face on it, as I tried a 90mph one and it gave a similarinaccuracy.:(I tried a friends 120mph speedo and it was accurate.

    Any idea if this is repairable?

    If not I was thinking I could possibly use a new 130mph speedo and see if I can swap my face over… not sure if the numbers would all line up though….

    There are no 120mph speedos on ebay at the moment – I don't want to end up buying another dodgy one!:?

    Anyone got a spare one they want to sell?:)

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    I believe the following is correct but no warranty given!

    With 10 inch wheels and 3.44 diff you should have a speedo with 1280 turns per mile as marked on the face of the dial, assuming you have 6/17 teeth on the mainshaft/speedo drive. It should be easy to check if the speedo drive is correct as for one turn of the speedo cable there should be 2.83 turns of the engine in top (assuming you don't have funny drop gears).

    The 90mph speedo you have probably requires 1408 turns per mile and works with a 3.76 diff with the same speedo drive as above.

    Before rushing out and buying a new speedo, I suggest you prove that the fault is not in the speedo drive.

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    You could always have it repaired and recalibrated at the same time – this chap comes highly recommended


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    The speedo drive is correct, as this was checked very recently with an engine and box rebuild. The speedo I have is the correct one for a Cooper S with a 3.44 final drive. A friend has an identical speedo, which gives the correct reading on my car, so the fault is with the speedo itself.

    I'm thinking the best option is to buy one of these


    And put my 120mph face on it, but not sure if it would fit. 70mph is at the 12 o clock position on both, so I suspect it would be fine! Wonder if the screw holes etc will all line up?:?

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    [b]Mk 3 S Meister wrote: [/b] “You could always have it repaired and recalibrated at the same time – this chap comes highly recommended


    Thanks for that. I might give him a call. Hopefully mine isn't totally beyond repair!

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    Don't start swapping guts yourself, you will never get it back together in anything like an accurate fashion, even if nothing else is altered the needle will go back in the wrong position and it will read high or low.

    The best bet by far is to contact JDO, Speedycables, Richfield Speedograph and get them to clean & recalibrate your original canibalised unit.

    It will come back as good as new and accurate, as long as you tell them it needs recalibrating.  Before you send it off they will ask you some facts about how it performs now and they will be able to send it back as good (if not better) than new.


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    Full details here;



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    Finally solved my speedo mystery! I removed the speedo drive again today, everything appeared to be in order, the plastic gear wasmeshing with the metal gear ok, and when Ipushed the car forwardsthe cable went round. However, the speedo itself didn't work, even though it was new, and it worked when an eletric drill was used to drive it.

    I stood for some time scratching my head…… Then I noticed…..:shock: The shaft was not securely attached to the plastic gear. When under load (speedo cable attached at both ends) the plastic gear was spinningon the shaft.

    Araldite is wonderful stuff 😀

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    A very good point……. 🙂

    I could have sworn I'd updated the thread to say that I had now got a working speedo, but that the speedoonly worked inthe car for a mile or so when the engine was stone cold……. I'm losing the plot in my old age!:)

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    tell you summat

    when you strip a early speedo down with the clear needle.its soooo easy top get the needle one millimetre out,before the rest stop,and it under reads or overeads like crazy

    i just rely on trial and error with the sat nav till i get it right now:)

    always was a bit of a cheapskate,lol

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    Yep, had to make a guess with mine, it reads 10mph too fast at the moment, I'll have to change it when I can be bothered to strip it all down again.

    I haven't felt like even looking at the car since I came back from Monte!:)

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    This trick only works OK if the speedo is un buggered about with in the first place!

    To put the needle back in the correct place:

    When dismantling the unit, carefully lift the needle over the needle stop so it goes behind the stop.

    Let the needle find its own place, usually about 1/4' behind the stop. stick a bit of masking tape on the face of the speedo and mark the EXACT spot the needle is positioned.

    Then when you re assemble the speedo you can put the needle back on in the exact correct place & won't have to guess.

    Works every time.


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    I have bits for 3 speedos and they all have a small white line in the vicinity of the main beam light. The two 90mph ones are in the same place and the 130mph is further back ie towards 6pm. Are these where the assembler is supposed to put the pointer? They seem to be in about the right place.

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    Having read this thread with interest I decided to check the calibration of my 130mph speedo. It read 4mph high at 70mph and I tweaked it down a bit. It is very simple to do on the bench.

    First check that you have the right guts as claimed on the front. Mine said 1280 turns per mile and I checked this with a hand drill counting turns of the drill. To check the mph you hook this up to an electric drill in reverse via the speedo cable and time how long it takes to clock up a mile (or ten miles if you want more accuracy). You do not need to know the speed of the drill. Calculate the 'correct' speed and compare this to the slightly wobbly indicated reading.

    To tweak the speedo, you need to take it apart and grab hold of the aluminium disc and then twist the pointer on the shaft a bit. I set mine to read about 1.5mph low at 70mph in anticipation of the road wheels going round rather faster than expected. If you do the arithmetic with a 3.44 diff, 6/17 teeth in the speedo drive and 1280 turns per mile, the diameter of the tyre should be 48.6cm. My brand new tyres unladen are 49cm which suggests that they will be rather less than 48.6cm laden, without taking any wear into account.

    Proof of the pudding will be in the eating when I have got my car on the road in a year or two.

    If the linearity is wrong, ie correct at say 70mph but miles out at 30mph, then best to send it to a specialist as there are no obvious tweaks the DIY bod can do.

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    my old speedo on my 60 morris mini minor basic(5 digit odometer) read ok upto 35 then massivly overead,..ie;90 mph at 50

    maybe this is beyond a tweak?

    ha ah

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    i refitted a used 5 digit unit,which worked well but mileoter stopped,i freed thiss off by using red rubber grease on the rotating cog that actuates the trigger arm,seems happy now

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