Speedometer Question with any abuse report

["Stephen Peca" <sppchicago@excite.com>]

 I recently purchased an TR3 speedometer on ebay (no regrets).
However, the pointer is very erratic and sticks at about 20mph when
stopped.  Did I get the wrong model speedometer?  If so, what should I
look for?  Am I missing something like grounding?  Or should I start
to locate another speedometer (the old one seized)?  Thanks.Steve
PecaAnnandale, New Jersey1958 TR3A - TS23867L