TRANSMISSION AND TORQUE CONVERTER 5540F/YB5515 SERVICE MANUAL
7-10 Published 10-21-2010, Control# 198-04
Hydraulic 2/4-Wheel Drive Unit
- Spring ON/Pressure OFF
4-Wheel Drive Operation (See Figure 7-10)
This clutch is of the 'Spring-ON (4WD)/Pressure-OFF (2WD)'
type. The clutch is engaged and disengaged by introducing
or dumping pressurised oil behind piston C via a solenoid
valve A. The solenoid valve is operated by a switch in the
cab.
When the switch is in the 4-wheel drive position, solenoid
valve A is de-energized. With the solenoid A1 de-energized,
the valve spool moves under the force of the spring A2. The
oil supply to the piston C is blocked, (shown at port 3). At the
same time oil vents from the back of piston C to the sump via
ports 1 and 2.
Because there is no pressure behind piston C, the clutch
friction/counter plates of clutch pack B are forced together by
disc springs D, thus driving the output yoke E.
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