Triumph Repair: 1977 Spitfire Speedometer, stock tranny, stock wheels

Question
Jim,
  I am replacing my Smiths speedometer with an aftermarket speedo and was wondering if you knew the gear ratio.  I am running a stock tranny and diff with stock wheels and tires.  The replacement speedo says it is designed for a 1:1 drive ratio (60 mph or 96,5 km/h at 1000 RPM) using a 5/8"-18 cable thread shaft. Do you know if this will work and if not is there a replacement drive gear available for it.
Thanks
Mark

Answer
Mark,

If you look at the speedometer face down near the bottom you'll see a 4 digit number.  That's the number of turns required for one mile.   Typically the number is in the 1030-1050 range.

The stock cable for the late Spitfire used a push on clip to hold it to the speedometer.  You might be able to get a cable from a Mk III or earlier that has the threaded fitting.  

Cheers,

Jim