A Mk1 66 (3-synchro gearbox) originally had the D-type overdrive as an
option, whereas in 67 the MkIIs (4-synchro gearbox) got the later LH-type.
The later one will probably not fit the earlier gearbox. The D-type came
with a vacuum switch and relay to delay disengagement of OD if there was
high manifold vacuum i.e. on the overrun at high-ish rpm to overcome an
inherent weakness in the design. The transmission tunnel was wider on the
MkII cars to accept the 4-syncro gearbox, so you can't put a later gearbox
in an earlier car without some metal bashing. The later seats may also have
been narrower/tapered to fit beside the later tunnel. The OD prop-shaft was
also 2.7cm longer at 78.9cm as opposed to 76.2cm.
PaulH.
----- Original Message -----
> I am going to pull my engine and transmission from my 66 MGB this summer
for
> a complete rebuild. I am considering installing an overdrive which it
does
> not currently have.
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