Re: [TR] Overdrive and Sppedometer

[DAVID MASSEY <dave1massey@cs.com>]

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 If Randall was still with us he could tell you when this happened.=C2=A0 I=
'm not sure when but I think it was right about this time.
In the olden days all gearboxes cam with the same speedometer drive gear an=
d the speedometers were calibrated based on the rear axle ratio.=C2=A0 If y=
ou look closely you will see a small print number indicating the number of =
turns per mile.=C2=A0 It could be some number like 1123 or 1056.=C2=A0=20

Then they adopted the more industry-standard 1000 turns per mile speedomete=
r.=C2=A0 With this scheme they would fit different speedometer drive gears =
according to the rear axle ratio.=C2=A0=20

You may be able to fix this with a different driven gear, which is easily i=
nterchangeable in situ from under the car.=C2=A0 You might check the archiv=
es.=C2=A0 There is probably a graph showing what color gear (they are color=
 coded) you need for the axle you have.=C2=A0 OD or no OD is of no conseque=
nce since the gear is driven off of the transmission output shaft.=C2=A0=20

Let us know what you find.
=20
Dave=20

=20
=20
-----Original Message-----
From: Jeff Scarbrough <fishplate@gmail.com>
To: Triumphs (triumphs@autox.team.net) <triumphs@autox.team.net>
Sent: Mon, Aug 24, 2020 8:13 am
Subject: [TR] Overdrive and Sppedometer

I have a 1975 TR6.=C2=A0 =C2=A0With the original gearbox, the speedometer w=
as correct.=C2=A0 I took it out to add overdrive and put in a gearbox from =
a 1974 while I worked on it.=C2=A0 That gearbox made the speedo read about =
12% higher.
Got the overdrive on the box and in the car.=C2=A0 My speedo still reads hi=
gh.=C2=A0 I'd like to find a simple solution...
Do I try to find the right drive gear for the gearbox output, or do I get a=
 different speedometer?

Jeff ScarbroughCorrosion Acres, Ga.** triumphs@autox.team.net **

Archive: http://www.team.net/pipermail/triumphs  http://www.team.net/archiv=
e

sey@cs.com

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<div style="color:black;font: 12pt Arial, Helvetica, sans-serif;">
<div> <font size="3">If Randall was still with us he could tell you when this 
happened.&nbsp; I'm not sure when but I think it was right about this 
time.</font></div>

<div><font size="3"><br>
</font></div>

<div><font size="3">In the olden days all gearboxes cam with the same 
speedometer drive gear and the speedometers were calibrated based on the rear 
axle ratio.&nbsp; If you look closely you will see a small print number 
indicating the number of turns per mile.&nbsp; It could be some number like 
1123 or 1056.&nbsp; <br>
</font></div>

<div><font size="3"><br>
</font></div>

<div><font size="3">Then they adopted the more industry-standard 1000 turns per 
mile speedometer.&nbsp; With this scheme they would fit different speedometer 
drive gears according to the rear axle ratio.&nbsp; <br>
</font></div>

<div><font size="3"><br>
</font></div>

<div><font size="3">You may be able to fix this with a different driven gear, 
which is easily interchangeable in situ from under the car.&nbsp; You might 
check the archives.&nbsp; There is probably a graph showing what color gear 
(they are color coded) you need for the axle you have.&nbsp; OD or no OD is of 
no consequence since the gear is driven off of the transmission output 
shaft.&nbsp; <br>
</font></div>

<div><font size="3"><br>
</font></div>

<div><font size="3">Let us know what you find.</font><br>
</div>

<div> <br>
</div>

<div style="clear:both"><font size="4">Dave </font><br>
<br>
</div>

<div> <br>
</div>

<div> <br>
</div>

<div 
style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original 
Message-----<br>
From: Jeff Scarbrough &lt;fishplate@gmail.com&gt;<br>
To: Triumphs (triumphs@autox.team.net) &lt;triumphs@autox.team.net&gt;<br>
Sent: Mon, Aug 24, 2020 8:13 am<br>
Subject: [TR] Overdrive and Sppedometer<br>
<br>

<div id="yiv3626171705">
<div dir="ltr">I have a 1975 TR6.&nbsp; &nbsp;With the original gearbox, the 
speedometer was correct.&nbsp; I took it out to add overdrive and put in a 
gearbox from a 1974 while I worked on it.&nbsp; That gearbox made the speedo 
read about 12% higher.
<div><br>
</div>

<div>Got the overdrive on the box and in the car.&nbsp; My speedo still reads 
high.&nbsp; I'd like to find a simple solution...</div>

<div><br>
</div>

<div>Do I try to find the right drive gear for the gearbox output, or do I get 
a different speedometer?</div>

<div><br>
</div>

<div><br>
Jeff Scarbrough</div>

<div>Corrosion Acres, Ga.</div>
</div>
</div>
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Archive: <a href="http://www.team.net/pipermail/triumphs"; 
target="_blank">http://www.team.net/pipermail/triumphs </a> <a 
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</div>
</div>

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