Classic/Antique Car Repair: 1930 ford madel a speedometer

Question
my speedometer spins very fast when driving . Where should I start looking to fix,

Answer
I am not sure what you mean  by spins very fast.  If it gives you a high reading, faster than you are going, then you have the wrong pinion at the transmission end of the cable.  Take it out and count the teeth.  Check the catalog, Snyders, to see if they have one with more teeth.

If it is trying to spin as you start rolling, then the magnet is rubbing on the indicator can.  That means you have to take the speedo apart and free it up.  Good luck,  jack