Regarding to the difference of ZF and Voith,here's something
that I could share with you guys:
1. Mercedes O.405G Habit
The Habit with ZF gearbox, will have a distinct 'cat yell'
produced. In some cases, you can't actually get hear it, as the
engine sound might covered it up. The ZFs are 4-speed gearbox,
therefore you could hear 4 distinctive change of gearbox. However
one has to beware about the slip gear change, ie the high pitch
yell in the beginning, to the lower yell of the next gear
change.
The Habit with Voith gearbox, do have distinct whistle, that is
produced when decelerating. Most of the O.405G Habit with Voith
gearbox are of 3-speed gearbox. However, the newer Habits, like TIB
1244 - TIB 1247, might have a 4 speed Voith, but no whistle
produced during the deceleration of the vehicle. However, one can
notice the Voiths by hearing the rather 'dry' engine sound.
2. Volvo Super Olympians & Tridents
Both of these double deckers from SBST do hold up the first gear
very long. This is because they are equipped with Voith gearbox. In
the Tridents, you can hear the whistle when they are decelerating.
In the Super Olympian, you would get to hear the gears retarding,
when they are at a pretty high speed.
NB: The Super Olympian Demo, ie SBS 9888 Y, is a ZF.
3. Volvo Olympian 3 Axle, Leyland Olympian 3 Axle, Volvo B10Ms,
TIBS Mercedes Benz O.405, Hino HS3KRKA, Scania L113CRB, Nissan
Diesel (UD)
These buses are using ZF4HP500 gearbox. They have very distinctive
ZF 'yell'.
4. Scania N113CRB, Volvo Olympian 2 Axle, Volvo B10M (DM3500)
These buses are using Voith gearbox. You can hear its whistle
during acceleration and deceleration.