Classic/Antique Car Repair: Speedometer 1957 Chevy, 57 chevy, battery terminals

Question
Hi, I just bought a 57 Chevy and the speedometer is stuck on 100. I would like to repair or replace it.  Can you tell me how I go about changing the speedometer?  I bought the 1957 Shop Manuel but it doesn't have any info about that.  Any info you can provide is greatly appreciated.

Answer
The instruments including the speedometer are held to the dash by screws that can only be reached under the dash. Before venturing under the dash disconnect the battery terminals! It is tighter quarters under the dash and you will need to lay down on the floor. I have been known to remove the front seat to make more of a space to lay down.
Brad