It's surprise after surprise with this car lately. 93 240, LH2.4, originally auto converted to M47, 200,000+ miles.

Today the wife tells me that she noticed the speedo was reading 38mph while she was on the highway, assuredly doing more than 38. I take it for a quick drive and sure enough, up to about 37/38mph the speedo seems to work fine, but then it just stays pegged there regardless of how much faster you go. No other noticable issues with the car, it accelerates beyond the point where the speedo stops, and everything feels fine. When you deccelerate it starts reading the correct speed again as you slow past 38mmph A firm smack on the dash doesn't change anything.

Any idea what could cause this? I probably have a spare somewhere, but I'd much prefer finding and fixing the problem over throwing parts at it. Especially because this problem could be outside of the gauge cluster.