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Re: Speedometer error with overdrive

To: triumphs@autox.team.net (Triumphs List), John Mitchell <jmitch@snet.net>
Subject: Re: Speedometer error with overdrive
Date: Sat, 12 Jun 2004 02:20:44 +0000
It has been a while since I had my OD apart, but I think the OD drive is held 
in place with a cross bolt.  Remove the bolt and the drive spindle is able to 
be removed without much trouble.  It can almost certainly be done from the OD 
access hole in the transmission hump on the passenger side.

Almost certainly the drive gear has the wrong number of teeth.  I forget how 
many teeth it is supposed to have, but someone here probably knows.  15 I think 
for the A-types.  

You do not say if you are reading high or low.  If it is reading high, the 
drive gear has too few teeth (probably by 1 or at most 2).  It the speedo reads 
low, then it has too many teeth.


An adapter gearbox in the speedo cable is a reasonable alternative.  They can 
get the calibration VERY accurate with them.  I am told that there are 4 gears 
which are interchangeable to give almost any ratio imaginable.  APT speedo can 
do it.  http://www.gaugeguys.com/ratioadapt.htm

-Tony



Hi Anthony,  My speedo says 1000, but Ive seen them(late model) that say 1120.  
I understand the change came at CF35000.  Im not sure if this overdrive even 
came out of a TR6, but it works flawlessly, so Im not too unhappy.  I made some 
calls today to speedo shops, and they can put a ratio converter in my 
speedometer cable, which seems like the easiest way to go.  My speedo is 
reading about 15% high, but I need to do some measured mile testing to get a 
fairly exact number before I go for the converter.   Changing the speedo 
driving gear looks like a pretty involved job(like a professional) so thats 
last resort.  Thanks for the reply,  John

Anthony Rhodes wrote:

John, do you know what year the OD is from?
 
For some reason I thought that all the TR6 speedos had the same calibration: 
1000.
 
What is the calibration printed on your speedo?
 
Probably you could get the correct speedo drive (at the OD) for your speedo and 
correct it.  Otherwise get the correct speedo....
 
-Tony





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