WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
76
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
Fourth Range
Before making the shift from third to fourth range, the
transmission control module (TCM) makes certain all
of the shift valves are in the correct position, with shift
valve 1 stroked and shift valve 2 and shift valve 3 de-
stroked.
Pressure control solenoid 1 (PCS1) is energized,
opening the PCS1 signal pressure to exhaust which
allows the pressure control valve 1 to de-stroke and
the 3rd, 5th, and reverse clutch pressure is exhausted.
PCS2 is energized, raising the PCS2 signal and PCS2
pressures. The PCS2 pressure is directed through shift
valve 1, shift valve 3, shift valve 2, and the manual
selector valve to the 4-5-6 clutch, applying the clutch.
Main pressure continues to fl ow through shift valve 3
and the manual selector valve to the 1-2-3-4 clutch,
keeping the 1-2-3-4 clutch applied. The TCM supplies
current to PCS2, which controls the rate at which
pressure control valve 2 supplies pressure to the 4-5-
6 clutch, and current to PCS1, which controls the rate
at which pressure control valve 1 exhausts the 3rd,
5th, and reverse clutch, assuring a smooth transition to
fourth range.
The combination of the 1-2-3-4 clutch and the 4-5-6
clutch application produces fourth range operation.
After the shift to fourth range is completed, SS3 is
energized, directing control main pressure to the top of
shift valve 3, stroking the valve. In the stroked position,
main pressure is redirected through shift valve 2 and the
manual selector valve to the 4-5-6 clutch, keeping the
4-5-6 clutch applied. Flow from pressure control valve 2
to shift valve 3 is directed through the manual selector
valve to the 1-2-3-4 clutch, keeping the 1-2-3-4 clutch
applied.
Pressure switch 3 turns ON and pressure switch 1
remains ON, providing feedback that the valves are
stroked. Pressure switch 2 remains OFF, providing
feedback that shift valve 2 is in the de-stroked position.
If electrical power is interrupted while the transmission
is in fourth range, PCS1, PCS2, the torque converter
clutch (TCC) solenoid, SS1, and SS3 are de-energized.
Main pressure continues to fl ow through shift valve 3
and shift valve 2 and the manual selector valve to the
4-5-6 clutch, keeping the 4-5-6 clutch applied. When
de-energized, normally open PCS2 exhausts the PCS2
signal pressure, allowing pressure control valve 2 to de-
stroke and the 1-2-3-4 clutch exhausts. After shift valve
1 de-strokes, the 1-2-3-4 clutch exhausts to exhaust
backfi ll. Normally closed PCS1 blocks the exhaust of
PCS1 signal pressure, allowing the PCS1 signal and
PCS1 pressures to rise. Pressure control valve 1 directs
full pressure through shift valve 2 to the 3rd, 5th, and
reverse clutch, applying the clutch. The combination
of the 4-5-6 clutch and the 3rd, 5th, and reverse clutch
applied produces fi fth range operation for a limp home
capability. If the TCC is applied, de-energizing the TCC
solenoid causes the TCC valve to de-stroke, exhausting
pressure from the top of the converter fl ow valve.
The converter fl ow valve de-strokes, redirecting main
