Continuation of a thread on the difference between speedo drives of LH
overdrives.
The ratio of an earlier (black label) LH OD is 21:8 or 2.625. The
ratio of a late (blue label) LH OD is 20:6 or 3.333. From what I can
gather the reason for the change is to rationalise (yeah, right)
speedos on the later models, i.e., the OD and non-OD cars used the
same speedo, which, of course, was different from either of the
earlier speedos.
In any case, the older OD had 2.625 turns of the output shaft for one
turn of the speedo cable, the later had 3.333. This means that a
speedo fit for an earlier model would read about 79% of the actual
speed. Now (of course) a speedo for an earlier non-OD tranny had yet
another ratio, and I presume this is what you have. Fortunately, the
difference between the earlier OD and non-OD speedos is only about 1%.
Bottom line: Your speedo is reading about 20% low. Don't go
over about 51 mph, but you will get there faster, at least in this
universe.
A. B. Bonds
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