401 / 405 Differential

[Geoff Kingston]

I have been speaking with the owner of a pre war BMW fitted with what is believed to be a 405 axle, what is certain is that it has the 4.2 ratio crown wheel and pinion. He is interested in a good differential we have just removed from a 401 axle as he wants to change over to the 3.9 ratio. I have looked at the 401, 404 and 405 parts books and it seems to me that this unit would go straight into a 405 axel case and work with the 405 half shafts but would be very grateful for a second opinion.
Geoff.