Specifications

Power Train Systems Operation
29
Forward Direction
Transmission Hydraulic System-Forward
(1) Transmission Oil Sump.
(2) Oil Pump.
(3) Primary Filter.
(4) Main Valve.
(5) Orifice.
(6) Inching Valve.
(7) Modulating Valve.
(7A) Load Piston.
(7B) Modulating Valve Orifice.
(8) Selector Valve.
(9) Solenoid Valve Forward.
(10) Solenoid Valve Reverse.
(11) Forward Clutch.
(12) Reverse Clutch.
(13) Relief Valve.
(14) Torque Converter.
(15) Relief Valve.
(16) Converter Bypass.
(17) Oil Cooler.
(18) Torque Converter Supply Bypass.
When the transmission is in FORWARD, the oil flow
from the reservoir, through the pump, primary filter,
torque converter and oil cooler circuits will be the
same as explained in NEUTRAL position.
Oil will flow from the main relief valve to inching valve
(6). Without inching (inching pedal up and valve in), oil
flows around and through the center of reducing spool
(6A) to the bottom of the spool. The oil, at the bottom,
pushes the spool up to the position shown. Oil flows
around the lands of the spool and through a passage
to modulating valve group (7).
In FORWARD, forward solenoid (9) is ON, so pump oil
is sent to the forward selector spool through oil
passage. Forward selector spool (8A) moves to the
right, causing reverse selector spool (8B) to move to
the right also.
With the reverse spool in this position, reverse clutch
(12) is open to drain, Forward selector spool (8A)
opens forward clutch (11) to pump oil. This also opens
reverse selector spool (8B) to drain through oil
passage. Forward clutch (11) will fill with pump oil.
Once filled, oil pressure begins to build up. Pump oil
goes through orifice (7B) and moves load piston (7A)
to the left as pump pressure increases. Oil pressure
increases as the load piston moves further to the left.
The pressure increases to the control pressure of 895
kPa (130 psi). Forward clutch (11) will now be fully
engaged. Modulating valve assembly (7) will now
shuttle between pump oil and drain to maintain clutch
pressure. Clutch fill time takes 0.4 seconds and
pressure increase takes 0.7 seconds. This
approximate 1.1 second clutch fill and pressure rise
time, gives a cushion engagement of forward clutch
(11).