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RE:Speedo for 4.10 rear

To: Randall Young <>, Triumph List <>
Subject: RE:Speedo for 4.10 rear
From: Tony Rhodes <>
Date: Mon, 8 Mar 1999 19:54:46 -0500

Indeed, It was me!  1325 is a very nice number and is in the right range.  This
is very interesting since it is not a whole multiple of 32!  In my limited
experience  I have only seen a 32 tooth worm-driven gear (later cars had a 20).
It looks like yours has a 25 tooth gear.  It would be VERY interesting to
get a look inside your speedo! OPen it up next time you have it out, and
count the teeth or turn the input shaft enough times for the pawl to make one
complete cycle.  

The 1180 is for a 3.7 rear, and is also interesting in that it would appear
to have a 20 tooth worm gear.  I had only seen that in the TR6 line.

Needless to say, I need much more baseline onfo on the available calibrations
in the various model years!

Yes, Triumph tried to find the closest to the required calibration.  The
worm gear tells us how close together the calibration options come.  If you
have 25 teeth, you may have to be as far off as 12, off by 10 for the 20 tooth

It sounds like you are positive about those numbers.  If you are I will
incorporate this info in my speedo manual!

Do you have an OD with the 4.1?

Message text written by
>Date: Sun, 07 Mar 1999 21:36:39 -0800
From: Randall Young <>
Subject: Speedo for 4.10 rear

Hi all :

I've lost the original post (Tony Rhodes, maybe ?), but ...

The speedo in my 59 TR3A appears to be for a 4.10 rear end.  The
calibration number on the faceplate is 1325, while my TR3 spare (also
from a 59, I think) has 1180 and a TR4 spare has 1184.  In every other
way, the TR3 units appears identical.
Although 1325 isn't exactly right (if 1180 is for a 3.70, 1325 should be
for a 4.15), it may be that there were a limited number of ratios
available, and Triumph chose the nearest one.  Another possibility is
that the 4.10 cars were fitted with shorter tires.  (1325 is within 1%
for a 4.10 axle and 165/75 tires.  1180 is within 1% for 3.70 & 155/85)


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