Ron:
I'm assuming that you have the original 3 synchro transmission in your
car.
There are a number of paths you can choose.
1. Stick with the original 3 synchro transmission. To add OD, you need
a complete transmission with OD attached. It's unlikely that you would
be able to find the OD specific mainshaft that is necessary to modify
your transmission, so plan on finding a complete assembly.
This is going to be tough, as they are not lying around in great
quantities. Early 3 synch boxes are usually going to need some major
rebuilding as they wear pretty quickly and there is usually tooth damage
to the 1st gear assembly. The OD unit is also not really strong, so
finding a good used one is going to be tricky.
Taking the time, trouble and expense to build a nice early box with OD
is a very honorable thing to do and if this is the path you wish to
take, I salute you. The early box has a lovely feel to it and a
correctly installed OD would really add to the uniqueness of the car.
I doubt very much if you will find a good used early transmission with
OD on Ebay, or other such venue. A rebuildable core unit would be worth
at least $500. A working used unit with warranty would be worth about
$1000, but it is questionable how long it would continue to be usable.
A rebuilding a core unit with warranty is going to be at least $2500.
There are a number of excellent rebuilding companies that will give you
an accurate quote and may be able to sell the unit outright to you.
Moss Motors does have one unit on hand available outright. It was
rebuilt in the UK where cores are more readily available and comes with
a 24 month warranty. The price is bloody expensive at $3,135.95, but
accurately reflects the cost of supplying such a unit. (I would love to
own it, but there is no way that I can afford to either.)
2. Convert to the later all synchro gearbox, with OD. It is still
feasible to find a good usable late gearbox with OD for a reasonable
price. The gearbox is pretty bullet proof, but they are now all at
least 25 years old. The OD is also solid, so good used ones are around.
There is a question about how long the OD clutch lining will last, as
there appears to be an age limit on the material. A failing clutch will
fill the box with fibrous material which is a bad thing. To install the
later box you would have to change the engine backing plate, starter,
flywheel and prop shaft to the later design. Some fabrication is also
necessary to relocate the gear shifter hole in the tunnel and cover.
This conversion uses readily available parts and is reversible. The
drawback is that the later gearbox has a heavier feel to the shifter and
is a heavier box. This conversion was very popular when parts
availability for the early gearbox was really poor during the 70s and
80s which is why my 1965 MGB is so equipped. Today, I would recommend
not doing this conversion, but would suggest going to a 5 speed, which
leads to...
3. Convert to a 5 speed transmission. This is a touchy subject as it
uses non-MG components. There are a couple of different transmissions
that can be used and members of this list have experience with all of
them. If you feel the need for extra gearing, then converting to a 5
speed would be a non-destructive and easily reversible solution to
easily get the car together and driving. For those who plan on driving
long distances, or who are not comfortable with the non-synch first gear
the 5 speed is a good choice.
Because I have spent a lot of time making it happen, I will abuse the
list slightly by stating that Moss Motors will be carrying the High Gear
T9 5 Speed Conversion kits for the MGA and MGB within the next month or
two.
I hope this lines out the options for you effectively.
Let us know what you choose to do, and how it goes.
All the best
Kelvin Dodd
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