Who cleaned and lubricated it? If you are measuring mileage correctly then you have the right speedometer. Odometer is a direct drive affair, while the speedometer is not. It has a magnet which turns inside of a cup. There is air space between the two parts. There is also a coiled hair spring involved which you cannot alter in any way while disassembling/assembling (which is quite a challenge without 3 hands, 2 of which needing to right-handed).
My guess is that it may not be properly cleaned or needs lubrication.

Last edited by 52Carl; 07/05/2017 12:06 AM.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission