The 1968 thru 1975 non-overdrive cars were equipped with the
small diameter 1280 speedo, the OD cars were equipped with a
different small diameter speedometer (a 1040 I believe). In
1976 the method of "calibration" changed. Both OD and
non-OD cars were equipped with the same small diameter 1000
speedometers and the OD trans and the non-OD trans were
fitted with the appropriate pinion gear to push the 1000
speedometer.
In 1977 the speedometer changed to the large diameter size
and remained a 1000. This setup continued through 1980.
In order to change a speedometer in a 1968-1975 car to match
the post 1974 OD you have to change the speedometer to the
one that came in a 1976 MGB.
This is all from memory (not researched) so fire away.
Larry Hoy
> -----Original Message-----
> From: owner-mgs@autox.team.net
> [mailto:owner-mgs@autox.team.net]On
> Behalf Of Kai M. Radicke
> Sent: Tuesday, December 21, 1999 1:22 PM
> To: Phil Bates
> Cc: David Councill; MG List
> Subject: Re: Does the OD tranny require a shorter
> drive shaft?
>
>
> Keep in mind that the 1280 O/D speedometer was
> not used throughout the
> 4-synchro MGB cars with overdrive, in fact I
> believe it is a 1971-1972
> speedometer only. What prompted our research
> into the matter was when a
> coworker's 1971 B was converted to overdrive, and
> we couldn't find the
> appropriate speedometer anywhere in our stock.
> Then Paul Barnes' most
> excellent 1972 MGB with overdrive was used as
> reference and still after not
> finding any differences, the three of us finally
> gave up and called
> Nisonger... which is when we were informed that
> it is only a face change.
>
> If I venture into work over Holiday break, I'll
> do a write up or
> something... one month off and I'm already bored
> 4 days into this vacation!
>
> Any wagers on how many phone calls the poor
> receptionist at Nisonger is
> going to get about this? ;-) Its an epidemic I tell you!
>
> BTW, Phil I think the company you mean on the
> West Coast is CARS... another
> division of Moss along with Nisonger (there are
> two Nisongers too, the other
> is not part of Moss Motors).
>
> Happy Holidays,
>
> --
> Kai M. Radicke -- kradick1@ic3.ithaca.edu
> '74 Triumph TR6 -- with 1001 spare parts all
> scattered about
> '66 MGB -- with a 1001% chance of heading for the
> scrap heap
>
> > I really can't say definitively if a different
> speedo is needed
> > or not for a 4 synchro. For the 3-synchro the
> gauge is the
> > same OTHER THAN THE INTERNAL GEARING which is
> > only about 5% different - a difference that one
> could come
> > out with from the wrong tires. Anyhow, like I
> said, I am not
> > sure with the 4 synchro - but I would suspect the same.
> > If you want to know and don't want to look it up call
> > Noisenger or that place in california (can't
> remember their
> > name, they both advertise in Hemmings). Be sure to ask
> > based on year, model with OD vs. not, and if
> the internal
> > parts are EXACTLY the same, or just close to the same.
> >
> > Phil Bates
>
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