Speedometer Trouble

I'm wildly guessing, as I've not done anything with a Mopar speedo so far. My best guess is some filth between the drive disc and driven disc that acts to spin the driven disc directly (rather than the normal spinning up gradually) until the filth begins to "roll" across the surfaces. This is assuming that these speedos work on the boundary layer effect and that the cable isn't binding from a weird angle or something. I suppose the same could be true if they use magnets or something of the sort. If it is caused by such a thing, disassembly and a can of air would probably kick it loose.

Crap. I've run out of abstract conditionals. ;-)