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Ellis
Joined: 07 Mar 2011
Posts: 1386
Location: Betws y Coed, North Wales
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 Posted: Tue Nov 17, 2015 12:16 am Post subject: Recalibrating a speedometer |
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Can I have some advice please.
I have recently changed the diffs on my 1962 Series 2a Land Rover to ex Range Rover/Discovery ones with a 3.54 to 1 ratio.
Before doing this I bought an ex Triumph GT6 speedometer which is as close to the recommended revolutions per mile speedo available - 1100, for the conversion to the new diffs and 7.50 R 16 tyres.
Now fitted, it works well but looks out of place on the Land Rover's binnacle.
Does anybody know where I can get the original speedo recalibrated to the recommended 1100 revolutions per mile.
The original speedometer (1508) worked perfectly but having "Googled" the subject it would appear that recalibration is only available with overhaul and repair of a speedo unit.
Any ideas ladies and gentlemen?
Thank you.
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1964 Jaguar Mark 2 3.4 litre
1962 Land Rover Series 2a 88"
2002 BMW M3 E46 Cabriolet |
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peter scott
Joined: 18 Dec 2007
Posts: 7215
Location: Edinburgh
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MikeEdwards
Joined: 25 May 2011
Posts: 2713
Location: South Cheshire
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| Posted: Tue Nov 17, 2015 11:40 am Post subject: |
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| How complex are the internals of the speedo? That is, would be it a very complicated job to place the internals of the one that works into the case and facia of the one that looks correct? I can't picture either of the speedos in question, so I apologise if that's a ridiculous idea. |
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MVPeters
Joined: 28 Aug 2008
Posts: 822
Location: Northern MA, USA
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| Posted: Tue Nov 17, 2015 11:53 am Post subject: |
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There was a short thread on this a few years ago - I think this will take you there:
http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=8434&highlight=recalibrate
But you might use a GPS to find out first if the original speedo is 'off' by enough to worry about.
I've also learned that it may be possible to change the speedo drive gearbox on the transmission.
Swapping the internals may be the best option; with care, it's not too difficult.
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2002 MINI Cooper 'S' |
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peter scott
Joined: 18 Dec 2007
Posts: 7215
Location: Edinburgh
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| Posted: Tue Nov 17, 2015 1:51 pm Post subject: |
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| MikeEdwards wrote: | | How complex are the internals of the speedo? That is, would be it a very complicated job to place the internals of the one that works into the case and facia of the one that looks correct? I can't picture either of the speedos in question, so I apologise if that's a ridiculous idea. |
This might be possible but the pointers are secured by virtue of a taper on the shaft and if the pointer doesn't easily rotate relative to the shaft then it is very easy to shear the shaft when attempting to remove it. Guess how I know that! 
Peter
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1939 SS Jaguar 2 1/2 litre saloon |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4241
Location: South Cheshire
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| Posted: Tue Nov 17, 2015 8:36 pm Post subject: |
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| peter scott wrote: | | MikeEdwards wrote: | | How complex are the internals of the speedo? That is, would be it a very complicated job to place the internals of the one that works into the case and facia of the one that looks correct? I can't picture either of the speedos in question, so I apologise if that's a ridiculous idea. |
This might be possible but the pointers are secured by virtue of a taper on the shaft and if the pointer doesn't easily rotate relative to the shaft then it is very easy to shear the shaft when attempting to remove it. Guess how I know that!
Peter |
not that difficult, but if a professional firm can do it for a £100 or so why bother?
Dave |
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47Jag
Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland
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| Posted: Tue Nov 17, 2015 8:54 pm Post subject: |
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| Quote: | | How complex are the internals of the speedo? |
The actual speedo mechanism is very simple. It has a magnet rotated by the speedo cable with an aluminium 'cup' placed over the magnet. The needle is attached to the spindle the cup is supported on. As the magnet rotates, the magnetic field drags the cup against a spring. The faster it spins the greater the drag on the cup and therefor movement of the needle. The calibration is done by varying the strength of the magnet to match the cable revs/mile to give the speed reading. This was how they did it in a place I worked at 50 years ago. I watched the specialist do it but never got involved myself.
The odometer (the mileage part of the speedo) is purely mechanical and needs the proper gearbox adapter ratio to be accurate. So in essence what I'm saying is you can get the speedo to indicate the correct speed but not the mileage travelled easily. It is a specialist job either way.
Art |
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Ellis
Joined: 07 Mar 2011
Posts: 1386
Location: Betws y Coed, North Wales
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| Posted: Tue Nov 17, 2015 9:31 pm Post subject: |
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Thank you all gentlemen.
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Starting Handle Expert
1964 Jaguar Mark 2 3.4 litre
1962 Land Rover Series 2a 88"
2002 BMW M3 E46 Cabriolet |
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goneps
Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand
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| Posted: Tue Nov 17, 2015 9:32 pm Post subject: |
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Speedograph Richfield make up adaptor gearboxes which effectively adjust the ratio. A bit messy, but tucked away beside the (transmission) gearbox no-one except yourself would notice. This would neatly solve the problem. Probably not cheap, though.
Richard |
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