Something else to consider when looking at speedometer accuracy
is the fact that our speedometers work off a couple of rotating magnets inside
the head. Over time these can get weak causing the speedometer to read slow.
They can also transfer some of that magnetism to the non-magnetic part and
cause a faster reading. An old speedometer repair guy once told me that the default for
most American auto makers was 1000 revolutions of the speedometer cable for
every mile traveled. Over time that should never change unless someone has
changed something in the transmission gears that feed the speedometer cable. My local shop tells me they can unhook the cable from the
transmission and plug it into their unit and verify the accuracy of the actual speedometer.
This would be my first step before trying to change gear ratios in the
transmission. Just my .02 Ken 67 Crown 4 Dr Ht 68 LeBaron 4 Dr Ht From:
mailing-list-owner@xxxxxxxxxxxxxxxx
[mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of sosmi@xxxxxxxxxxx Graham, it would seem a significant reduction in tire
diameter, would be necessary to be 10 mph off at 70 mph. thats assuming it was
correct before tire replacement.I would check actual gear ratio, then compare tire
diameters, from original and the present.The FSM has a chart in the trans
section, that gives specs for speedo pinions according to gear ratio, and
tire size.Ya'll have a nice day, Dave.
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