Listers,
Anyone out there want to swap an excellent 1973 model O/D for a late model O/D
so I can get my speedo to read correctly on my 78B ?
Jim in Harleysville, PA (34 miles NW of Philly)
Larry Hoy wrote:
> James, I think you're in trouble. I now think that there are no 1280tpm
> speedos that are the 4" size. Turns out that the first chart on Skye's
> site is missleading and the 1280 speedo listed as 1967 is really for a
> 1968 model car which is the smaller 80mm size.
>
> What all BMC manufactures did in 1976 was change to a standard 1000 tpm
> speedo and made the gears in the transmission work for the speedo.
> Prior to that the speedos were unique tpm for each car. (For instance
> your gauges are the same gauges found in the Triumph Spitfire).
>
> You may need to resort to some 'extremes'.
>
> 1) An electronic speedo from VDO
>
> 2) A transmission from a speedo shop
>
> 3) A new face plate for your present speedo (I thought that Nissonger
> did this)
>
> When I put in my V8 in the car I had to do the #1 option, since I have a
> Chevy 5 speed transmsission. I've attached images of the small VDO
> speedo gauge. The biggest 'give-a-way' is the red tip on the needle,
> and the digital odometer. I used the stock MG facia ring.
>
> Larry Hoy
>
>
> > Subject: Re: Speedo calibration bust!!! OFF LIST
> >
> >
> > Larry,
> > Thanks for the info. I'll wait for your final analysis.
> > Jim
> >
> > Larry Hoy wrote:
> >
> > > > That's a different size speedo... it wouldn't fit in your dash.
> > >
> > > Max, Jim, Bill,
> > >
> > > I could be wrong but I think the 1963-1967 and the
> > 1977-1980 cars are
> > > the 4"(100mm) instruments. The 1968-76 cars are the 3 1/8" (80mm)
> > > instruments.
> > >
> > > His OD transmission is from a 1973 car that was originally matched
> > > with a 1280 tpm 80mm speedo. His car was originally built with a
> > > 100mm 1000tpm speedo. According to Skye's web site the
> > 1967 cars were
> > > equipped with a 1280tpm 100mm speedo. Soooo the 1967 1280tpm 100mm
> > > ought to fit in his dash and solve the problem.
> > >
> > > Consider that his car goes 60mph and registers 80mph a
> > ratio of 1.33
> > > (80/60). The speedo ratio would be 1280/1000 which is 1.28; almost
> > > identical. After the change the 60mph car should register around
> > > 62mph. I bet if Jim REALLY knew how fast he is going when
> > his present
> > > speedo is registering 80 mph he'd find he is going 62.5 mph
> > which is
> > > what the 1280 tpm speedo would register.
> > >
> > > There is the one 'gotcha', I'm not convinced that Skye's charts are
> > > accurate. In fact he has two charts on his site that seem to be in
> > > conflict. (By the way this is why I've copied Bill Dudley with this
> > > message, his 1967 MGB is a one owner car. Bill, would you
> > check your
> > > speedo and see if it is a 1280 tpm 4" speedo?). I suppose
> > that will
> > > be sorted out when we here from Bill, who I think is out of
> > town right
> > > now.
> > >
> > > Max the 21 vs. 22 tooth gears wouldn't be able to make enough
> > > difference to even justify the change. The gear INSIDE the
> > > transmission that drives the pinion changed over the years, that is
> > > another solution. However it requires the removal of the engine,
> > > transmission, and then the swapping of the internal speedo
> > drive gear.
> > >
> > > On other solution. Any COMPETENT speedometer shop can make a
> > > transmission to change the ratio.
> > >
> > > OK now one last suggestion, then I'll quit. VDO makes a 4"
> > gauge that
> > > is programmable.
> > >
> > > Larry Hoy
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