On Fri, 01 Apr 2005 07:01:24 -0800, dougmcp wrote:

There are a couple of possibilities. Given the vintage of your
car, it's possible that there has been an incorrect replacement
of one part or another, throwing off the overall speedometer drive
ratios. This one is dead simple to check. Find a highway. Note your
odometer reading. Drive about 20 miles, watching the mile markers.
Watch the odometer to see if it's clicking over about the same time
after each mile marker. And, oh yeah - do watch the road. If your're
odometer is turning over nicely at the same point from each mile marker,
then the drive ratio's are correct. (Note: this is for the mechanical
speedos - you know, the one's with a spinning drive cable and geers -
the newest electronic units "drive ratio" is done by a counter in a
chip - which in some cases, can also be "adjusted")

If your odometer is NOT kicking over at the same point after each
mile marker, your overall ratio is off. Take note of how far off it
is after 20 miles - the speedo shop may want this info.

In either case, any good speedo shop should be able to help. There
are a variety of reasons a speedo can be reading wrong, depending
much on the design of the speedo and whether it's the older
mechanical rotating magnet design or one of the slightly newer
electronic coil designs, or the latest digital designs.

http://www.nhspeedometer.com has been in business longer than
a lot of us. I won't claim that they have bargain basement
prices, but I've used them twice and they did what they were
supposed to do.

Conrad