RE: speedos & L vs S gearing

["Brian Shorey" <bshorey@domain.elided>]

> I need to get the right speedo calibration for my newly 4.1 geared Verde
and
> have the following observations that should also apply to electronic
speedo
> GTWee6's:
> - sending units and under-seat amplifier are same for any combination of
> gearing, car and X-axle;

not entirely true - the late gtv6 and milano sending units are the same, but
the early gtv6 and late gtv6 senders are most definitely different.  one is
gear driven and one is sealed.

> - speedos are driven directly by a small electric motor and odos
> are driven by same motor but thru a gearset;
> - speedo motors are labeled with the # of giri per meter (revs per
distance)
> or vice-versa;

the sending units are also marked with this number, and it differs between
the early and late gtv6's (and presumably the milano as well).

> - compared a US 2.5 speedo motor with my Metric 3.0 speedo and found: the
> odo gearing, the # of giri per meter and angle of sweep of the indicating
> needle are all different.
> There is a bunch of circuitry associated with controlling the speedo motor
> and that may be what determines the speed of the motor relative to the
rate
> of pulses from the sending unit in the tranny.

i believe that there are two, and only two types of senders.  one is from
the pre '85 gtv6's, and is gear driven, the other is from the post '85 gtv6
and milano, and is sealed.  they have different pulse rates from each other.

i have an '82 gtv6, and when i went to replace the 85 mph speedo with a 140
mph one, it indicated exactly half of what the actual speed was.  i located
a different 140 mph speedo and it worked fine.  the pulse rate indicator on
the new speedo matched what was on the sender.  i would guess that the
difference in final drive between the 3.41 gtv6's and the 4.10 gtv6's (and
between the 3.55 milano's and the 4.10 milano's and late 4.10 gtv6's) is
accounted for somewhere prior to the sending unit.

now, the million dollar question - i'm almost ready to install my gear
lightened platinum transaxle.  i believe i have two options - (1), wire the
milano sender into the gtv6 wiring harness and use the 140 mph gtv6 speedo
that didn't work before, or (2) open the tranny and rework the internals to
allow use of the original gtv6 sender (if that's even possible).

has anybody done either of the above, and if so, what worked?

bs

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End of alfa-digest V7 #762
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