I may be way out in left field on this one but the only way I think this could
happen is for something to be slipping. A binding cable won't do it and you
would notice the needle bounce if it was.
The right angle gear for the speedo cable on the tranny may be the culprit. The
gear could be warming up by the end of your drive and is slipping on the shaft
internally. It is possible that the slippage could occur in the little gimmo for
the emissions servicing indicator if it is still there. I doubt that this would
warm up as much as the one on the tranny.
Just a guess. Let us know the results when you find the solution.
Vic Whitmore
76 Spitfire
Thornhill, Ontario
Kirby T. Kenyon wrote:
>
> I've got a weird one on my '80 Spit.
>
> I drive the NYS Thruway to work. When I drive my Spit, early in the
> drive the Speedometer reads the correct speed (70MPH @ 3400 RPM with OD,
> verified by time over mile marker method) but approximately 30 miles
> later, it reads low (63MPH @ 3400 RPM).
>
> I verified that I was still going about the same speed at the end of the
> trip that I was in the beginning so I know there is no slip in the drive
> train.
>
> Could this be a symptom of a slightly binding speedo cable? It does
> bounce some at lower speeds but smooths out about 30MPH.
>
> Has anyone else encountered this?
>
> Kirby
> '80 Spitfire
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