Message text written by Patrick Bitton
>Someone on Ebay is selling a speedometer that claims it's for OD
transmissions. I asked him the difference and he told me that "Revolutions
are different for the OD compared to the non OD. One is 1000 and the other
is 1120." Is this true? Do I need to replace my speedometer to get a right
reading? It seems that when I feel that I am going 50km/h, the reading is
about 30km/h. Has anyone experienced this while doing this conversion?
<
This is only slightly correct. Since the speedometer is driven from a gear
on the output shaft of the transmission, the only thing that matters is the
rear axle ratio. Now, a car with overdrive you could use a different axle
ratio (4.11 in lieu of the 3.7) and still have resonable revs on the road.
If this was the case a different speedo head would be called for (at least
on the early TR6's - later TR6's all used the same speedo head and chaged
gears in the transmission).
>It seems that when I feel that I am going 50km/h, the reading is
>about 30km/h. Has anyone experienced this while doing this conversion?
My recommendation is to find a streach of highway with distance markers
each Kilometre where you can run a consistant 60 KPH and time the markers.
At 60 you should be passing a marker each minute. Find the speedo reading
at which this happens. In fouth direct you should be running 1,875 RPM.
(This assumes you tach is accurate, too) If the speedo reads 67 then you
just may have the wrong speedometer. If your tach reads 2,100 RPM you just
may have the wrong speedometer. Or they may just need calibration. But
rather than judging speed by "how it feels" compare you speedo reading
against a known standard. (And using a pace car's speedometer is not
always accurate)
I put overdrive in my TR6 (and the TR3, too) and had to change nothing in
terms of the speedometer.
Dave
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