Subaru XT 1988 Service Manual page 700

3-3 TRANSMISSON CONTROL SYSTEM
MECHANISM AND FUNCTION
4WD Shift Mechanism (Selective 4WD)
Shifting from front-wheel to 4-wheel drive or vice versa is accomplished by utilizing the intake manifold vacuum pressure.
In Front-Wheel Drive
@
4WD Pilot lamp switch
Intake manifold vacuum
Diaphragm
Lever (transfer shifter)
(j)
Rear drive shaft
4WD solenoid valve
I
(Atmospheric pressure)
Check valve
CD
4WD switch (PULL)
®
4WD pilot lamp
___ 0--+--'----
Power source
@
Intake manifold
Fig. 1
L3-235
When the 4WD switch button
CD
is pulled out with the engine
on, the FW[) solenoid valve
®
is energized and the valve
®
opens. This admits the intake manifold
@
vacuum pressure
to the vacuum chamber so that the diaphragm is pulled in the
direction of the arrow.
At this point, the power from the engine is not transferred to
the rear drive shaft
(j)
and thus the vehicle is in front-wheel
drive. The 4WD pilot lamp
®
in the combination meter
remains off because the 4WD pilot lamp switch
®
is not
turned on.
2