Steve:
Proceed with caution here. The fact that both your tach and
speedometer are reading high makes me think that there may have been a
gearing change made at some point. Perhaps a rear end swap (4.10 gears?)
or a transmission swap such that the speedo and tach now both appear to
be wrong.
While you say how you determined that the speedo was reading
high, you did not say how you decided that the tach is high, or at what
engine speed it is reading high. Is it 500 RPM high at 3,000 RPM for
example? If so, then the tach and speedo are both roughly 10% high,
which hints that the root cause is the same for both the speedo and
tach.
It just seems unlikely to me that BOTH the speedo and tach would
go out of calibration at the same time by about the same amount in the
same direction. More likely that your DPO made a change that did this,
unless of course your ARE the 'DPO' and you know that both instruments
were at some time correct. In THAT case, I would suggest that you are on
the right track with calibration.
Cables are not capable of making the speedo and tach read high.
They can make the instruments jump and bounce, because the cable binds
and then releases. Usually a little oil is all that is required to fix
this.
But if both instruments are steady, and consistently read high,
then you are back to calibration or gearing. By the way, if it is
gearing, I do not recommend merely having the speedo recalibrated (tach
would be correct in that case and would not be recalibrated), as your
odometer will still be off and you will add on 'mileage' faster than you
probably want to. Better to make a gear change to the speedo drive to
correct the inaccuracy, which will also correct the odometer.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Steve Lindquist
Sent: April 18, 2005 6:25 PM
To: 6pack@autox.team.net
Subject: Speedometer out of calibration?
Yesterday I had my daughter drive behind me on a stretch of interstate
to check my speedometer. At 70mph indicated on the TR she reported just
over 62 on her car. I also have a tach that reads high by approximately
500 rpm, no overdrive and tires that are 185SR15 on my TR250. That
would make the circumference about 5% greater than original, which
should make me faster than indicated, not slower. Do these instruments
go out of cal, or is it more likely cable issues or ..?
Steve Lindquist
508.869.6709
lindquistse@charter.net
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