Hi,
To install an overdrive you need to:
1. Remove the gearbox, strip it and replace the mainshaft with the
correct overdrive version. This has splines at the end to drive the
overdrive. Alternativey change the whole box. The mk3 as standard has a 3
synchro gearbox which can only be fitted with the 'd' type overdrive.
Later gearboxes have 4 synchros and later still the 'j' type overdrive
was fitted which is stronger. If you fit a later box you may (or may not)
need to change the clutch and possibly the flywheel to get the splines to
mate up.
2. Change the propshaft for the overdrive version (about 3" shorter), or
get yours shortened by a specialist. Note that the 4 synchro box is 3/8"
longer so it has a shorter prop.
3. Change the gearbox rear mounting plate to the overdrive version.
4. Install electrics (relay and switch). For a mk3 the steering column
switch would be the standard way of doing it but the gearknob switch
could just as easily be fitted if you prefer.
Good luck,
Keith Bennett Keith.Bennett@bbc.co.uk
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