TD speedometer help

[bobd@dynacomm.fse.com (Bob Dallas)]

I need your advice--
I took the TD around the block--this is the first time it had been under its
own power in 25 years.  The speedometer didn't work and I don't know if it
worked 25 years ago. I unhooked the brand new cable from the speedometer and
it didn't turn when the car was moving-- Which means that the pinion is not
tuning in the gearbox.  How should I approach determining the cause?

BTW--it was wonderful! 
Bob Dallas
Houston, Texas
'69 MGB-GT  '51 MG-TD