Just finished rebuilding a Hvan gear box. Washed it out with diesel when I'd finished then filled it up,with some 20/50 new but not what I would call top quality oil to flush it out ran it up then drained this and it looked the same as when I put it in ...when completely drained refilled with a G5 ran this up and drained it and it was frothy (we still had 20 litres of g5 which we don't use anymore in our 2cvs as wrong spec so was just using it up ) drained this and re filled up with G4gear oil and when checked level no frothing !!!,

not enough anti-foam additives or additives that react with gearbox/bearing materials?

NSC - what oil are you actually using in your re-built H-van box?

And is it any quieter after the rebuild?

Thanks

Maybe the filling level with the unwanted GL5 grade oil was rather generous and the higher level of oil in the gearbox introduced a 'blender' effect?

I spin rebuilt A series gearboxes with an electric motor and the oil level does have an effect on whether or not aeration will occur.