Classic/Antique Car Repair: 1931 speedometer problem

Question
how can a person trouble shoot a speedometer installed in the car that does not work. The 1931 Model A runs fine. The installed speedometer looks good(don't know if ever worked)cable assembly is installed and attached to the transmission. Any suggestions to determine a problem before removing complete assembly?

Answer
What usually happens is that the main bearing in the head of the speedo tightens up and is very hard to turn, and it breaks the cable.  It is rather hard to fix this problem.  Let's hope you don't have that problem.  Jack up one wheel, Put it on a jack stand, don't trust the jack, block the car from moving, make sure the wheel is free to turn, be very careful, and start the engine and put it in third and let the clutch out.  The jacked wheel will turn, and while it is turning, observe the speedo cable.  It should be turning.  If not, something is wrong at the trans, or the cable is broken.  Now take the speedo head and try to turn the center shaft with your fingers.  It should turn easily.  If not, the bearing has tightened up and broken your cable.  
This should let you determine where the problem is, and if you do have to fix the bearing, I can help you with that.  Good luck.  jack