The transfer box is the heart of the technical innovation in the FF. For this reason there is much interest among collectors regarding the transfer box numbers. Usually, the last three digits of the transfer box number are close to the last three digits of the chassis number. It appears that Jensen may have once intended to synchronise the two numbers,
but in the event, very few cars has the same transfer box and chassis number.

Typically, as the car left the factory the number would be within 10 or so numbers of the chassis number. FF 123 had gearbox number 130, for example. FF 11 currently has gearbox number 20, which was more than likely the original gearbox for the car.

In the event, it appears that the transfer boxes were numbered up in batches, and a given car would be given a gearbox at random from the batch currently in the factory...

Also, if a gearbox was returned to the factory for rebuilding, the factory would send by return a previously rebuilt gearbox off the shelf. Also, over the years, many cars had gearboxes switched out and swapped by enthusiasts.

Although it is nice to have the transfer box fitted at the factory, it is equally interesting to discover how a car came by the transfer box it currently has. This can often unravel interesting history about the car, especially when the original gearbox is eventually located in another vehicle. Perhaps the cars had a common owner at one time, and pictures of the two cars together can be unearthed, etc...

Interested FF owners can identify their gearbox number most easily by examining the last three digits of the number stamped into the rear face of the transfer box. When viewed from the rear of the underside of the car, the number can be found below the output shaft on a smooth plate cast into the casing, and to the left of the fluid filler/level plug.

The photograph below, taken from the rear underside of the car (the rear right silencer can clearly be seen). shows the location of the number highlighted in pink.