Specifications

Power Train Systems Operation 28
Reverse Direction
When the transmission is in REVERSE, 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 REVERSE, reverse solenoid (10) is ON, so the
pump oil is sent to the reverse selector spool through
an oil passage. Reverse selector spool (8B) moves to
the left, causing forward selector spool (8A) to move to
the left also.
With the forward selector spool in this position, forward
clutch (11) is open to drain. Reverse selector spool
(8B) opens reverse clutch (12) to pump oil. This also
opens forward selector spool (8A) to drain through
passages. Reverse clutch (12) will fill with pump oil.
Once filled, oil pressure begins to build up. Pump oil
goes through orifice (7A) 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(130psi). Reverse clutch (12) 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
ressure increase takes 0.7 seconds. This approximate
1.1 second clutch fill and pressure rise time, gives a
cushion engagement of reverse clutch (12).