To remove the internal workings of the speedometer, you need to remove the glass bezel, by cutting and pulling out the crimped metal that holds the glass in place.
There are no parts available to repair the speedometer, you have to cannibalize another speedometer, send it in for a costly repair, or buy another one .
The tachometer has a printed circuit card inside with semi-conductor components, corrosion and cracks in the board and solder joints have caused problems in the past.