How the Magnetic Speedometer works
Very simply using the drawing (Left). Inside the speedo housing, the speedometer cable connects up to a small frame which holds the magnet and worm assembly (5), on the outside of the frame are two small magnets. As the car moves the magnet frame spins around. Cupping the magnet frame but not touching it is a small aluminium drag cup also called the drum spindle and bush (6). Connected to the cup is the needle / pointer. As the magnet frame spins, it creates an eddy current which draws the aluminium cup around against a small hair spring.(7) The faster the magnet frame revolves the more the drag cup is drawn round and of course so is the speedometer needle. Simple!
The MK3 Nemag