Speedometer rebuilding. No info

i had a 74 duster that speedometer bounced,took gauge cluster out, at the end of the speedometer cable is a round housing,it had two magnets, i could put a small screwdriver on one and it would pull to the magnet, the one on the other side wouldn't pull the screw driver had lost its magnetism, i replaced just the speedo, $30, whitepunkonnitro on a bodies down Murfreesboro had the speedo i bought