Designing the Caterham transmission was another major challenge.  As the Caterham has a narrow body, I had severe restrictions to the width available.  The footwells for the driver and passenger run alongside the transmission, so I had a maximum width of around 5 studs to package everything in!  I decided early on that a 6 speed transmission would be impossible without spoiling the realism of the rest of the design, so I settled on a 4 speed setup.  I then realised that using the conventional setup, with the gear lever directly above the gear driving rings, would result in the gear lever being much too high.  So, I designed a  linkage mechanism to enable the gear lever and driving rings to be mounted one behind the other, reducing the height.  This uses 8 tooth gears to mesh with the driving rings.  The drive from the differential passes between the centre of these two linkages to the front of the transmission.

The 24 tooth gear mounted right at the front acts as the output from the transmission, and drives the engine via an 8 tooth gear.

Update:  The 24 tooth gear shown has now been replaced by a 20  tooth gear due to a minor re-design.

The rather complicated drive from the differential to the main driveshaft via four 8 tooth gears and two 14 tooth bevel gears is simply to minimise the space taken up in this area.

The second image shows the full drivetrain.  This gives a good impression of the compactness of the gearbox area.

The photos demonstrate the installation of the transmission into the vehicle.