FIVE SPEED GEARBOX

For years people have complained that the Mini required a fifth gear. Although many years ago the idea was
tackled by Felday, Coletti Francis and Jack Knight, these gearboxes suffered through being either too
complex to make, awkward gear changing or poor reliability. The basic problem with the Mini was, that,
although tairly quick off the mark, it lacked "legs" on the motorway. The only way to solve this was to fit a
higher final drive ratio, killing the Mini's sharpness off the line. An "all or nothing" choice. Several people
and companies took a serious look at solving the problem, realising the potential in sales and company
promotion. To produce a functional, compact easy to assemble and above all reliable five speed gearbox
conversion for the Mini was a major engineering feat on a box that has always carried inherent problems.

Most five speed boxes have the fifth gear as a direct drive with 1-1 ratio. It was quickly evident that this set up was not possible, but a ratio of less than 1-1 would have to be used and it could
only be fitted to a rod change gearbox. Tran-X were given the project and as David Hirons, the
owner, pointed out, "there is more to this than meets the eye". As Mini Spares demanded a proven product, the idea involved much thought, and design changes midway, with fabrication of parts to get to a finished product. Working models were built, modified or scrapped and it became obvious where others had tried and failed miserably. Certain seemingly unimportant but significant areas were overlooked. The result of all this painstaking development is a five speed gearbox solely designed by Dave Hirons of TranX under licence to Mini Spares, that not only runs quietly, but is suitable for everyday use (road or race) with an inherent strength over the original.

Much of the redesigning had been put into simplifying the conversion so home-assembly by a reasonably competitent individual was possible. The kit contains over 35 pieces and to all intents and purposes, the design work is almost over-engineered! - Strong enough to withstand torque inputs of over 220lb more than any 'A' series engine is likely to deliver. Careful consideration was given to final drive ratios as this could easily have become a restrictive choice, but this was dealt with in the overall design so that any final drive ratio could be used. Essentially the conversion can be fitted to any gear assembly that can be fitted into a rod change gear case. The gearbox case and laygear needs modifying and a new speedo housing is supplied to hold the gears. Therefore the gearbox will be sold on an exchange basis in kit form, with all parts and gears for introducing a fifth gear including a special speedo housing. Customers will have to exchange their gearbox case and laygear as extensive modifications are carried out on these two parts. Customers will retain their own diff assembly and mainshaft with all gears and bearings. The ratio will be 0.86 on 'A' plus and 0.87 on non 'A' plus gearboxes, which will reduce 3.44 to 2.96 and 2.99 respectively. An optional ratio of .91 or .92 is also being looked at.

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