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Overdrive origin

To: "Triumph Digest List" <triumphs@autox.team.net>
Subject: Overdrive origin
From: "Dave Rogers" <roggez@bigpond.net.au>
Date: Tue, 25 Oct 2005 09:18:52 +1000
    I am currently helping a friend complete an overhaul on his 62 TR4. 
Having done a nut and bolt job on mine six years ago, at least some of the 
know-how has not faded! I am seeking some information on his overdrive, so 
if anyone can point me in the right direction, I'd be grateful.
    When we pulled the engine, I saw the overdrive was a J Type rather than 
the usual A Type in a 62 TR4. I checked the serial number and the first two 
were 26, indicating a 26% reduction ration as is the clue on Laycock de 
Normanville units. I am aware that the A, in the TR4 had a 22% ratio and I 
understand the early Js fitted to the TR6 in the early part of their 
production run were a 23% model.
    All my references mention the model fitted to Vanguard sedans had a 28% 
ratio but nowhere can I find reference to the 26% model.
    Can anyone help as to the possible origin? It works OK but I would like 
to replace a few bits and a steer in the direction of possible alternate 
sources of supply (ie cars in yards) would be of help.

Dave Rogers
Canberra, Australia
62 TR4 CT12038-O
72 TR6 CC80026-O (was U but R-ighted and PI'd) 


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