>Date: Wed, 6 Feb 2008 06:59:40 EST
>From: DLylis@aol.com
>Subject: [TR] 3A Speedo
>To: triumphs@autox.team.net
>Message-ID: <bc1.279fe84a.34dafb2c@aol.com>
>Content-Type: text/plain; charset="us-ascii"
>
>I am in the process of rebuilding my 3A Speedo. What I noticed, >and didn't
>seem odd to me at the time is that the little number under the >odometer that
>indicates the number of turns per mile is 1216. Randall pointed >out that to
>his knowledge that should be 11XX, like my TR6 speedos are >1120. Can anyone
>shed some light on this?
>Could you TR guys out there take a look at yours and let me >know what you
>see?
>
>David Lylis
>69 TR6 CC26160L
>60 TR3A TS74461LO
I am not positive of the original calibration for a 3A, but I think it would be
something like 1184 (maybe 1200?). The 1216 calibration would give a +2.7%
error. You could probably notice this amount of error on your odometer, but
probably not on your speedometer.
If you had an original 1184 calibration, then the "stock" overdrive of a 4.1
ratio would change the speedo calibration by the ratio of 4.1/3.7. IOW, the
same car fitted with a 1184 speedo would need a calibration of 1312. It would
appear thar your speedo is not close enough to the 4.1 differential
calibration. (N.B. An overdrive made to fit these cars will not change the
speedo calibration because the speedo drive comes off after the OD and it is
supposed to have the same number of starts on the scroll as the non-OD
transmission)
These speedometer faces are reasonably unique to the TR line. I have not seen
these faces on other cars, but I certainly have not seen every one ever made!
Therefore, I would wager that the 1216 was a stock configuration for SOME early
TR with SOME size of 15" tires.
My website has a monograph on this subject that might be helpful.
http://home.comcast.net/~rhodes/speedo.html
-Tony
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