I have to admit that I didn't know that the single rail/J-type units use a
replaceable gear for
speedometer compensation. I have not dealt with any
of the more modern boxes and the earlier 3-rail and D-type OD units don't
use this sort of function.
It sure makes it easier to guess what
speedometer to use if everything is the same!!
Joe
Patrick Barber wrote:
>
> Joe, Patrick
> The late model spitfires used a 1000 rev/mi speedo and compensated by
> changing the speedo gear. I figured this out the hard way when I
installed
> a J-type OD in my MK3 Spit. The speed indication was way off. Lucky for
me
> I had a late model speedo with 1000 rev/mile. I place the guts of this
> Smiths speedo and placed the Jaeger faceplate and needle on top of it.
Once
> installed, everything worked fine.
>
> I think the 1000 rev/mile has become a standard. I have contacted XJ's
> Unlimited, a Smiths speedometer suppler and all their speedos are now 1000
> rev/mi.
>
> Patrick Barber
> Allen Park, MI 48101
> patbarber@home.com
>
> -----Original Message-----
> From: owner-spitfires@autox.team.net
> [mailto:owner-spitfires@autox.team.net]On Behalf Of Joe Curry
> Sent: Thursday, April 12, 2001 11:45 PM
> To: Patrick
> Cc: stag@digest.net; spitfires@autox.team.net
> Subject: Re: Speedos OD 1000 - 1184 - 1248 - Stag
>
> Patrick,
> I don't know what you did when you added your OD unit, but the Spitfires
> with and without OD use the same speedometer. This is because the speed
is
> measured on the output in both cases. So unless you also changed
> differential gearing, or the the diameter of your rear wheels, I can't see
> how you
> could have changed your speedometer reading.
>
> But looking at a number of speedometers I have lying around, I think your
> assumption is correct. The early Spits with 4.11 rear gears had a 1248.
A
> 1500 with a 3.89 diff has a 1184. I'm not sure what the 1000 came from
but
> I would suspect based on calculations I have done with the other numbers
> that it is a 3.27 from GT6. Finally, I have a speedo that came from a
GT6
> and it is numbered 980. That is so close to the aforementioned 1000 that
> I suspect it was for a 3.27 diff with slightly larger diameter rear tires,
> making the final gearing very slightly higher than the 1000.
>
> Regards,
> Joe
>
> Patrick wrote:
> >
> > OK all
> > I'm still stuck on this Speedometer thing with the Stag and OD.
> >
> > As y'all know my speedo reads 72 when it should be 60
> >
> > Spitfires had 3 speedo types. the numbers in the front were 1000 ,
> 1184
> > and 1248(jaeger mk1)
> >
> > When I added an overdrive to my spitfire, the speedo was off, I
> changed it
> > from a 1000 type to a 1184 type, (or vice versa can't remember) It made
> it
> > correct.
> >
> > So I took 72 x 1000 / 1184 and got 60.8 MPH
> >
> > I believe (and correct me if I am wrong) that the numbers 1000 and
1184
> and
> > 1248 mean the number of revs for 60 MPH or maybe 100 KMH
> >
> > So all of you with Stags and original OD's does your speedo on the
> bottom of
> > the dial face read 1184?
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