Well, actually there are two units, and it has to do with
different rear end ratios (3.7:1 vs 4.11:1) that were used.
Since the different rear ends usually corresponded to
whether or not an overdrive was fitted (although I suppose
you could order a non-OD car with an OD rear end) the OD
and non-OD cars had diffrerent speedos. I'll try to look
the part numbers up tonight (unless someone beats me to it).
Bruce Clough
> From triumphs-owner@autox.team.net Thu Aug 27 06:01:16 1998
> From: KTRIUMPH@aol.com
> Date: Thu, 27 Aug 1998 05:54:47 EDT
> To: jrobins@nwc.net
> Cc: triumphs@autox.team.net
> Mime-Version: 1.0
> Subject: Re: TR4 Speedometer - OD vs. non-OD
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>
> In a message dated 98-08-27 01:04:34 EDT, you write:
>
> << 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
> There is no "overdrive" speedo unit. An OD doesn't change the rpm of the
> output shaft in relation to the rear wheels. Same speedo.
>
> Ken Nuelle
> 58 TR3A
> 62 TR3B
> 64 TR4
>
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