One way I've just thought of would be that the rear diff sometimes has a sticker on it saying what it is.
Also, in case you didn't see my wanted thread I'm looking for a 3.9 box to replace mine that these bits came out of yesterday...

Cheers,
tommo.
No, input shaft is the same regardless...Callum89 wrote:Is it possible to tell if a gearbox is a 3.7 or a 3.9 from the number of plines on the gearbox input shaft? My gearbox has 24 splines and the diameter is 24mm.