Jordan,
I was one of the folks to talk about '6 speedo units. I believe the
discussion is the same for the '4/4A. There is a fixed tooth counter
gear on the tailshaft of your tranny. The tooth count is the same for
the non-OD and OD transmissions. The speedo unit 'counts' the number of
revolutions the tailshaft turns and converts that to a speed indicator
and odometer counter. It is the responsibility of the speedo unit
calibration to get the conversion right. Unfortunately, changes in diff
ratios and/or tire size will affect the accuracy of the conversion,
causing an under/over speed depending on the final drive rations
achieved.
The Smiths speedo units have the 'conversion rates' printed on the
outside edge of the front face. For the '6, I have found two numbers,
1120 and 1000 turns per mile. I don't know what the numbers are for the
'4/4A. My understanding is that these units can be calibrated (by who?)
for accuracy, and they were accurate +/- 10% out of the factory. I've
even heard rumors that the factory installed the incorrect units in the
later '6s so the U.S. folks would think they were zipping around (can
you conform John Mac?).
Scott Mackay
Austin, TX
Date: Wed, 26 Aug 1998 22:07:00 -0700
From: "J. Robinson" <jrobins@nwc.net>
Subject: TR4 Speedometer - OD vs. non-OD
Anybody on the list know how to tell an OD calibrated speedo from a
non-OD
speedo on a TR-4? There was a thread on this recently covering TR-6
which
jogged my curiosity since I have a similar problem, a speedo with mph
consistently running 6-7% fast on my non-OD equipped TR-4.
Jordan Robinson
CT28864
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