omega0684
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| posted on 4/6/06 at 12:03 AM |
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smiths speedo
hi all,
just a quick question, could i use this speedo i found on ebay even tho it says its from the states
http://cgi.ebay.co.uk/Brand-new-Smiths-MGB-Speedo-USA_W0QQitemZ4643928069QQcategoryZ27380QQrdZ1QQcmdZViewItem
cheers ALex
I love Pinto's, even if i did get mine from P&O!
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Alan_Thomas
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| posted on 4/6/06 at 08:36 AM |
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I used this type of speedo but you have a lot of work if you want to use a mechanical speedo.
Bear in mind to get thru the SVA it has to be up to +3% +3mph and never read less then true speed.
So it depends on your tyre size and pressures, diff ratio,speedo takeoff gear and the internal ratio of this speedo. All this ensures will definately
will be reading wrong.
You then have 2 'adjustments' in the speedo head to do to get it right You have to unsolder the hairspring and either let it off a bit
(unreading) or pull it bit more thru (overreading) and the second type of adj is where the position where you push on the needle.
Took me at least 10 attempts to do this with the instrument in pieces tearing up and down a long drive comparing it to a handheld GPS.
You can send off the head to Richfield Speedo and they will calibrate it (they ask you to accuratly turn the back wheel 'x' times and
count the revs the cable is doing and push the car so that the wheel turns exactly 'y' times and measure the distance travelled.
It not a cheap service either.
If I were doing it again I would go the electrical route it so easy to calibrate.
I still think these instruments l'ook right' in these cars though!
- Alan
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britishtrident
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| posted on 4/6/06 at 10:45 AM |
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You need to know the turns per mile (TPM) for both the speedo and your speedo drive.
The speedo is easy it is written on the face of the speedo in a tiny font somewhere around the bottom of the dial. The TPM should be a 3 or 4 digit
number between abouut 900 and 1150. I think MGB spedos are about 1000 tpm.
Getting the tpm for your locost drive train is a bit tougher -- but it might just also work out to 1000 tpm -- mine did. (Sierra type 9, 3.89 final
drive, 185/60x14" tyres, Triumph Spitfire speedo.
Smal difference in calibration can be calibrated out but large difference are a no-go.
[Edited on 4/6/06 by britishtrident]
[Edited on 5/6/06 by britishtrident]
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