Spastic speedometer....I need some help.

[bca10]

Hello, I have 1990 240 sx with a regular instrument cluster. (no hud). The speedometer works sometimes but most of the time the needle sits at 10 mph when I get up to speeds of 55+. I think the speed sensor sits just below the starter and I have inspected it and there doesn't appear to be anything wrong with it. No shorts, bare wire, or poor connection. Any help would be greatly appreciated. It is a 5 speed.