Adding Overdrive to a 4 speed manual

[Mike Wattam <MikeWattam@domain.elided>]

Hi Dean

Yup, grab the 'box.

As you might have seen in other recent e-mails, the 'box itself is not Stag
spec, but the overdrive is.  

It is possible to have the gearbox uprated to 'Stag' spec, but not cheap. 
If your 'box is an early example the gear teeth will be incompatible with
the Stag layshaft, and will also need changing.  If you wanted to swap the
'box as well, it is almost worth running the gearbox in unmodified trim to
see if it can stand the pace!

The gearbox really needs to be on the floor to fit the o/d, as it is
complex lining up the internals of the overdrive with the 'box mainshaft,
and easy to damage.

As you do not have overdrive at the moment, you will need to change the
gearbox mainshaft - easy to say but slower to do - so you will have the
'box on the floor anyway.  You can use the Innsbruck mainshaft to save a
lot of expense - they are in short supply anyway.

The propshaft is shorter to mate with the overdrive 'box.  If you are
certain your own propshaft is good, there are a number of prop specialists
in the UK who can shorten, recondition and rebalance these.  However, the
Stag prop has a rubber insert which may make this impossible - seek advice.
 Alternatively, service exchange props can be obtained from Stag
specialists but these are usually of the cheaper solid variety.

The exhaust pipes from manifold to front silencer are a different shape and
might foul the overdrive, but these are relatively cheap to renew and you
will need them off anyway to remove the 'box.

Then it is just a case of gearlever, switch and knob, wooden surround and
adding the overdrive inhibitor switch to the side of the gearbox cover and
wiring harness to suit, so the overdrive will only operate in 3 & 4.

Time to get fit and get those biceps bulging.  Not only to lift the 'box,
but also to dig in your pocket.  Hey, ho.

Mike Wattam
Chairman - Triumph Stag Register