i have two 3tj gearbox's in a box of spares, one is a rr box & one is a sp, i know the sp has a taller 1st gear than the RR, but does that meen first gear is larger or smaller ie more teeth or less teeth than the other ?

A higher gear will travel a bigger distance per revolution so the gear should be larger .... hopefully

cheers for that evil thats what i was thinking

in a constant mesh gearbox theres two actual gears that make up a "gear". a driven gear and a drive gear. They are constantly in mesh togather. The drive gear is fixed to its shaft (layshaft) and driven by the engine. The driven gear is free from the shaft and driven by the drive gear. count the number of teeth on both, then divide them, this will give you the ratio.

a taller "gear" will have a smaller driven gear, but will have a larger drive gear. larger gear doesnt necisarrily mean has more teeth either, some times the same gearbox will have very different pitches of gears in them.