This has been on the net earlier, but from memory (I'm at work and
don't have my references available), here's the basic approach/
The quesion concerned a 67 tach that read way too high (about double
was the observation.) Later tach folks can sign off now. Their
tachs are different. Earlier electronic tach folks can stay with us.
There is a small "volume control" inside the tach, but you must
remove the tach from your dash, remove the back of the tach (the can)
and reattach the wires you removed to get this far. This "volume
control" is adjustable with a small screwdriver. I'm talking small
here, like typewriter repairmen used to carry around in their shirt
pocket. Jack up the rear end of your car and put jack stands under
the axle at each rear spring. Climb in the car, and holding the tach
that you removed from the dash, removed the back (can), and
reconnected all the wires to get this far, (with me so far?).
Holding the tach so that you can see the "volume control", start the
car. Tach should read as before you removed it. Now adjust it with
the "volume control". With the car in 4th gear and wheels turning at
55mph (per speedometer that you have confidence in), set the tach to
read 3000rpm. Turn off the car and reassemble and reinstall the
tach. If you have a dwell meter that has a high speed tach (up to
3000rpm or so), Forget the wheel spin at 55mph. Just adjust the tach
to read the same as the standard (the one in the dwell meter). If
you don't have a dwell meter with a hish speed tach and you have no
confidence in your speedometer --- follow somebody with a speedometer
that you do trust. Mark it for "true" 55mph and follow instructions
above.
Failing all that, take the tach out of the dash and send it to one of
several places indicated in the monster list for recalibration.
Failing that, smash it and file a claim under your car ins. (Just
kidding here. My brother in an insurance inversigator.)
Go for it.
Bill Olson
Arkansas State University
72 Tourer, 67 Grand Tourer
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