WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
70
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
Second Range (Without TCC Applied)
Before shifting from fi rst to second range, the
transmission control module (TCM) makes certain shift
valve 1, shift valve 2, and shift valve 3 are in the correct
position with shift valve 1 and shift valve 2 de-stroked
and shift valve 3 stroked.
Pressure control solenoid 1 (PCS1) is energized,
opening PCS1 signal pressure to exhaust and allowing
pressure control valve 1 to de-stroke, exhausting the low
and reverse clutch pressure. PCS2 is energized, raising
PCS2 signal and PCS2 pressures. The PCS2 pressure
is directed through shift valve 1 and shift valve 3 to the
2-6 clutch. The TCM provides current to PCS2, which
controls the rate at which the pressure control valve 2
supplies pressure to the 2-6 clutch, and current to PCS1,
which controls the rate at which the low and reverse
clutch is exhausted, assuring a smooth transition to
second range. Main pressure continues to feed through
shift valve 3 and the manual selector valve, keeping the
1-2-3-4 clutch applied.
The combination of the 1-2-3-4 and the 2-6 clutch
application produces second range operation.
After the shift to second range is complete, SS2 is
de-energized allowing shift valve 2 to de-stroke. The
low and reverse clutch feed, which was exhausted
through shift valve 2 and the PCS1, now exhausts
through exhaust backfi ll, keeping the low and reverse
clutch released. The 3rd, 5th, and reverse clutch has
an exhaust path through shift valve 2 to the pressure
control valve 1, keeping the 3rd, 5th, and reverse clutch
released.
Pressure switch 1, pressure switch 2, and pressure
switch 3 turn off, providing feedback that the valves are
in the de-stroked position.
If electrical power is interrupted while the transmission
is in second range, PCS1 and PCS2 de-energize.
Normally open PCS2 exhausts the PCS2 signal
pressure, allowing pressure control valve 2 to de-stroke,
exhausting the 2-6 clutch. Normally closed PCS1 blocks
the exhaust of the pressure control valve 1 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 1-2-3-4 clutch continues to be
applied with main pressure through shift valve 3 and
the manual selector valve. The combination of the 1-2-
3-4 clutch and the 3rd, 5th, and reverse clutch applied
produces third range converter operation for limp home
capability.
If the torque converter clutch was applied during the
power interrupt, the TCC solenoid is de-energized and
the transmission returns to converter operation.
If electrical power is interrupted while the transmission is
in second range and subsequent third range operation,
moving the manual selector valve to Neutral (N) will cut
off main pressure to the 1-2-3-4 clutch and the clutch
will be exhausted. The 3rd, 5th, and reverse clutch
remains applied. Because only one clutch is applied, the
