Hi There

Does anyone know what this weight does?

what gearbox?

Yes

I was under the impression the weight is to reduce notchy gear changes

Just improve the feel.

Was my understanding also but on the Getrag 5 speed box in the Rovers they use different weights depending on the which of the 3 type of engine are used so that points to it being a tuned mass damper to cancel out vibrations in particular RPM bands

http://en.wikipedia.org/wiki/Tuned_mass_damper