[Neilnaz]

Don't know much about g50 gearboxes but often grinding from 5th to 4th is 'touching reverse' which is due to poor adjustment of the coupler. It sounds like the coupler and bushes need to be examined to ensure that you are not 'touching reverse' on your way to 4th.

This may only apply to 915 gearboxes but I imagine it is possible for g50s too.

Cheers, Neil