WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
73
2007 W Series Chassis
WSM082106
Second Range (With TCC Applied (Tow-Haul))
Energizing the torque converter clutch (TCC) solenoid
strokes the TCC valve against the stop, allowing
main pressure to fl ow to the top of the converter fl ow
valve. The converter fl ow valve is stroked, exhausting
converter-in pressure to sump, and eliminating the
separating force between the TCC piston and the
converter cover. At the same time, the converter fl ow
valve opens the passage supplying TCC-apply pressure
to the converter-out circuit. The pressure differential
across the TCC piston applies the torque converter
clutch.
Depending upon the calibration, TCC solenoid could be
energized in ranges 2-6. The calibrations can also apply
the TCC for special applications such as power take-off
(PTO) operation controlled directly by engine speed with
transmission in neutral or TCC operation in fi rst hold.
Third Range
Before making the shift from second to third range, the
transmission control module (TCM) makes certain all of
the shift valves are in the correct position with shift valve
1, shift valve 2, and shift valve 3 de-stroked.
Pressure control solenoid 2 (PCS2) is de-energized,
exhausting PCS2 signal pressure which allows the
pressure control valve 2 to de-stroke, exhausting the 2-6
clutch. PCS1 is de-energized, raising PCS1 signal and
PCS1 pressures. The PCS1 pressure is directed through
shift valve 2 to the 3rd, 5th, and reverse clutch. The
TCM reduces current to PCS1, which controls the rate at
which the pressure control valve 1 supplies pressure to
the 3rd, 5th, and reverse clutch, and reduces current to
PCS2, which controls the rate at which pressure control
valve 2 exhausts the 2-6 clutch, assuring a smooth
transition to third range. Main pressure continues to fl ow
through shift solenoid 3 (SS3) and the manual selector
valve to the 1-2-3-4 clutch, keeping the clutch applied.
The combination of the 1-2-3-4 clutch and the 3rd, 5th,
and reverse clutch application produces third range
operation.
After the shift into third range is complete, SS1 is
energized and directs control main pressure to the top
of shift valve 1, stroking the valve. With shift valve 1 in
the stroked position, the 2-6 clutch feed is exhausted
through shift valve 1 to exhaust backfi ll keeping the 2-
6 clutch released and the 4-5-6 clutch has an exhaust
path through shift valve 1 to pressure control valve 2,
keeping the 4-5-6 clutch released.
Pressure switch 1 turns ON, providing feedback that
shift valve 1 is stroked. Pressure switch 2 and pressure
switch 3 remain OFF, providing feedback that shift valve
2 and shift valve 3 are in the de-stroked position.
If electrical power is interrupted while the transmission
is in third range, SS1 and the torque converter clutch
(TCC) solenoid (if TCC is applied) are de-energized.
Shift valve 1 de-strokes, changing the exhaust path of
the 4-5-6 clutch to exhaust backfi ll and the exhaust path
of the 2-6 clutch to pressure control valve 2. Normally
