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Spitfire Spitfire Speedometer "Calibration"

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doates

doates

Senior Member
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Spitfire Speedometer "Calibration"

Hi Everyone,

In all my fooling around taking the speedometer in and out while working on the dash wiring, the speedometer needle has gone from swinging wildly to rock solid at about 20% faster than I am driving. I installed a D Type overdrive from an unknown car; purchased on Ebay so I am surprised that it works. I am assuming that the right angle drive gear is not correct for the Spit.

Does this make sense?

Thanks in Advance
 
Re: Spitfire Speedometer "Calibration"

Could be, but IMO it's more likely to be the speedo drive gear inside the D type.
 
Re: Spitfire Speedometer "Calibration"

Thanks,

Is that changeable/findable? I would not do anything about it until I have reason to take my transmission or interior out but it would be nice to have one around when I do.
 
Re: Spitfire Speedometer "Calibration"

Sorry, I'm not too familiar with the Spitfires; I'm not certain which gear you would need. But I see PN 506119 available from TRF & Canley Classics (no doubt others, but I only checked those two); and it might even be changeable without removing the transmission from the car. If you can get to the angle drive to unscrew it from the OD, then you can probably undo the locking bolt and pry out the bearing assembly with the drive gear in it.

But the gear is a bit pricy, so I'd want to confirm that is the problem, first. Have you confirmed that the odometer or trip meter also reads high? If not, then the problem is the speedo mechanism itself. I can't explain why, but I was just working on a TR3 speedo the other day that was reading some 30% high for no apparent reason.

AFAIK, the angle drive should be 1:1 ratio, so you can check that too.

Another possibility perhaps, you might just not have the right speedo head to match your differential and tire size. Here again I'm not certain if this extends to Spits; but for the earlier "big" Triumphs, the ratio in the gearbox/overdrive was constant and the speedometer itself changed for changes in final drive ratio and tire size. Later TRs always used a 1000 turn per mile speedo, so putting a late speedo in an early TR causes it to read ... about 20% high.
 
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