Jack,
In the TR4/4A cars it is possible to swap transmissions between the
non-overdrive version and the overdrive version. In fact I am now in the
process of such a conversion. I believe that this conversion is also
possible on the TR3 series cars, but you may need to get an A (not a J
type) overdrive to be period correct. The J type overdrives are correct
for the TR6. You may also want to swap in a synchromesh tranny for the
earlier non-synchro unit supplied on the TR2 and early TR3 cars.
I obtained a well used type A overdrive transmission and the requisite
parts to rebuild it, including some rather hard to find
replacement gears, which altogether cost me something
over $600, and now I am gradually rebuilding it. The overdrive unit is
attached to the rear of the bell housing and is cylindrical, about a foot
in diameter with electrical solenoid and wires attached. The overdrive
transmission uses a shorter output shaft to drive the propeller shaft. The
non-overdrive transmission is distinguished by a narrow housing about two
feet long and with a box section which is attached to the bell housing,
and by a longer output shaft. The overdrive switch for the TR4 and later
cars is on the steering column, but I think that the earlier cars had it
on the dashboard. The additional parts to make the conversion are
available from the usual suppliers. I hope this helps.
Best Regards
-Kevin
'67 TR4A in progress
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