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Good  luck with your project’...  Enjoy your classic motoring...
Fixed price repairs are based on the assumption that unit/s received
‘original & complete’... a surcharge may be applied to cover
missing  parts etc...  If in doubt send in the unit for inspection

If  you  found this web site via a ‘search engine’ please
 check that you are looking @ the
latest version... click here
Mileage correction
Other services
Post & packing
Contact details
Rev counters
Jaguar XK 120 ( 1948 / 54 )
1109.1 M
Parts Order E-Mail Link
Payment options
Payment options
Payment options
Payment options
JDO Instruments
Classic Car Instrument Repairs ( Est 1963 )
Fixed price repairs for most British & European Classic Car Instruments
48hr service  
available... Why pay more & wait longer ! No UK vat
Tele: (UK)  01535 672125 (2 lines)  Mobile: 07831 886545
Please check the  FAQ’s page  BEFORE ringing / emailing... thank you
Information required to Check / Re- Calibrate a Speedo
                                                                                                                    print off a copy & enclose with your order...    
*Jack up just 1 Driven wheel  Measure the Circumference of the fitted tyre in inches  = _______  cms  = _______
Remove the Speedo...make up a cardboard pointer or similar & fix it to the end of the exposed inner speedo cable
Put a chalk mark etc on the edge of the tyre & the ground ...
Now  turn the
‘Jacked up’  wheel 20 turns forward ( out of gear )
& count the number of turns the speedo cable makes = ___________  to the nearest 1/8 ( eighth ) of a turn

* The above assumes a Normal diff unit ... if the car is fitted with a Limited slip diff  ( LSD)...
Jack up
 Both driven wheels  & turn one wheel 10 turns forward ( out of gear )
take up the ‘LSD’ slack first  ie. until the OTHER wheel starts to turn  ( approx ½  turn  )  this will give the same result
Please state the FULL tyre size _____________________    & type eg.  Radial  /  Cross-ply  ( delete one )

However if your car is on the road & running ask a friend etc to pace you in another car *  with a speedo known
to be ok... ie. set the
Trip on both cars to zero ... Travel approximately 10 miles / 16 Km & advise both readings
eg. True distance = _______  Your cars indicated distance = ________  to the nearest 1/10 ( tenth ) of a mile / Km
Or use a ‘reliable’ Sat-Nav  
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Calculation page
Calculation page
Calculation page 1
Re-Calibration surcharge
Re-Calibration surcharge
Re calibration surcharge