My darling 340U, perm sv. 242 bus. I took it lots of times. That
sound is not the engine. Listen carefully and you'll find that it
is actually coming from the rear wheels Yes, It is the groan of the
hub-reduction axle (hubs for short). This is the bugger with the
loud hubs. (I recall putting it up as 482T, my humblest
apologies.)
What is a hub-reduction axle? If you notice, the rear axle of the
Mercedes O405 has a large cylinder shaped thingy. Inside that
thingy, there are gears. The gears help in moving the bus and
reduces the amount of power needed from the engine. The Mercedes
OM447h engine, used on the O405, is normally aspirated.
The O405s have quiet hubs but they have gotten louder due to age.
You can hear the hubs on a fully loaded O405 as the extra weight
packs more pressure on the axle. But it is still not loud enough
and is usually muffled by the loud engine, except in the case of
340U. There's virtually nothing wrong and please please please
please please do not fix it. This is what makes the O405 unique and
this is what the true blue bus fan will look out for.
