Hydrostatic Transmission; When Driving; Function - Yamaha WR450F 2-TRAC Supplementary Owner's Service Manual

HYDROSTATIC TRANSMISSION

WHEN DRIVING

Driving a two wheel driven motorcycle is different from driving a conventional motorcycle. The front wheel
drive system, during certain conditions, affects the feeling of the handlebar. In sand, mud and snow the
traction is greatly improved. However in conditions with deep ruts and slippery surfaces the two wheel
drive system might contribute to that the motorcycle feels heavier and more brutal.
WARNING
It is of absolute necessity that the two wheel drive motorcycle has a steering damper. If driven
without steering damper the front wheel, when hitting a root or a stone, can give unduly high
reaction forces to the handlebar.
Before racing, practise as much as possible on different tracks and under different conditions to
get used to the different behaviour of the two wheel drive system.
CAUTION:
On rough road surfaces the front wheel drive can make the steering harder. This is noticeable,
especially when driving aggressively.
When landing after jumps the two wheel drive system will make the front fork feel stiffer due to
that the driving force tries to extend the front fork, especially if the throttle is applied before
touchdown.
NOTE:
This 2-Trac system has been tested extensively on both test tracks and in races. Imperative for the dura-
bility and function is high quality material in all components. The high quality materials used are not
always the best suited to provide beautiful surface treatment. As a result we can sometimes see shades
and/or mis-colouring on the anodised aluminium surfaces.

FUNCTION

With the motorcycle free rolling, the pump rotates roughly with the same speed as the
motor.
When throttle is applied the rear wheel and thereby the pump, due to deformation of the
rear tire, starts to rotate a little bit faster even if the driving force is just large enough to
maintain constant speed.
The increased volume stream from the pump causes the speed of the motor to increase,
but to a lesser extent than the pump, thereby creating a driving torque from the front
wheel. Thus the amount of front wheel driving force varies with speed and ground condi-
tion and comes in gradually depending on throttle position.
The system has a maximum pressure relieve valve installed to prevent dangerously high
pressure in the system, when for instance on slippery surfaces, where excessive rear
wheel spin can occur.
The oil in the transmission can sometimes get very hot. For instance in sandy, slow
speed conditions or when trying to escape from a mud pit. In order to prevent damage to
the transmission a built in thermostat valve shortcuts the hydraulic circuit, thereby discon-
necting the front wheel drive. When this occur a couple of minutes cooling time is needed
to get the system back into function again.
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