I have the same rear end/tire set up as Alan.
After a rolling measurement get a requirement of 1113.62 speedo TPM
Because of this issue (and my neurosis about accurate instrumentation ! ),
have just installed a stepper motor style digital speedo. This is a near
exact replica of the original Smiths as fitted to the BJ8 with blue high
same fonts etc. Only major difference is that the ODO/Trip is now a small
LCD; it and needle is driven by a pulse transducer that you install by
cutting the speedo cable; easy to make TPM mods.
Most people don't notice the difference at first glance.
Could post a pix if anyone is interested.
Sent: Sunday, December 4, 2016 1:34 PM
To: Bob Haskell
Cc: Healey List
Subject: Re: [Healeys] speedo questions
For what it's worth I have found that 1152TPM is the closest calibration I
could get to suit the set up on Bluehealey. I have a 3.54 Lempert diff on
overdrive box with 180XAS Michelins. Rolling radius of those I found to be
The set up uses a 32tooth worm wheel and 36 tooth Odo wheel. The displayed
mileage and actual mileage are pretty close and have been checked over a few
hundred miles against a Sat Nav. Error is about 1-2%.
Your tyres will be the only variable with my arrangement.
Speedo calibration is all over the place. I just moved the needle, relative
to the drive cup, until 60mph matches my sat nav display. All other speeds
above and below will be off a margin.
Give me your rolling radius of the tyres and I will be able to provide the
best Turns per mile sett up.
Alan - from my iPad
> On 4 Dec 2016, at 19:32, Bob Haskell <firstname.lastname@example.org> wrote:
> What's the thickness of the washer that is fitted between the gearbox and
> the right angle drive (PN 3H550 or Moss PN 324-720)?
> There are two MPH speedometers fitted to the 3000 MkI and MkII; one for
> overdrive and one for non-overdrive cars. What's the speedometer
> calibration (turns per mile) for each?
> BMC P/N Smiths P/N TPM
> non-OD BHA4124 SN6155/19 980???
> OD BHA4126 SN6155/21 1080???
> When fitting a 3.54:1 rear end to an overdrive equipped car, does the
> non-OD speedometer have the correct calibration? I think that it would if
> the gear ratios for the speedometer takeoffs on the extension housing of
> the non-OD gearbox and on the overdrive were the same. If not, what
> calibration (TPM) have folks used?
> Bob Haskell
> AHCA 3000 MkI registrar
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