Speedometer recalibration

["Justin Hughes" <ka1ult@xxxxxxxxxxxx>]

Hi...

I just replaced the somewhat inaccurate 85mph speedometer in my '83 320i
with a 120mph speedometer from a '79 320i.  From the gear ratios, I know
that 3000rpm in 5th gear is 65mph.  However, I'm getting readings closer to
80.  My diff is a 3.91, compared to the 3.64 that came with the earlier
320i, and therefore the speedo reads a higher speed than it should.  The
inaccuracy is a consistent percentage at all speeds, so with a number of
reference points I can determine how far off it is, then get it recalibrated
to account for the different diff, lower profile wheels, etc.  Can anyone
suggest somewhere near the Boston area that can recalibrate my speedometer?
I know some places advertise in Roundel, but since I drive the car routinely
I'd rather not have to take the time to ship the speedo across the country
to get it calibrated. Thanks.

      - Justin

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