WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
82
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
Sixth Range
Before making a shift from fi fth to sixth range, the
transmission control module (TCM) makes certain that
all shift valves are in the correct position. Shift solenoid
1 (SS1) and SS2 are electrically off and shift valve 1
and shift valve 2 are in the de-stroked position. SS3 is
electrically on and shift valve 3 is in the stroked position.
Pressure control solenoid 1 (PCS1) is energized,
opening PCS1 pressure to exhaust, which allows
pressure control valve 3 to de-stroke, exhausting the
3rd, 5th, and reverse clutch pressure and releasing
the 3rd, 5th, and reverse clutch. PCS2 is energized,
raising the PCS2 signal and PCS2 pressure. PCS2
pressure is directed through shift valve 1, shift valve 3,
shift valve 2, and again through shift valve 3 to the 2-6
clutch, applying the clutch. Main pressure continues to
fl ow through shift valve 3, shift valve 2, and the manual
selector valve to the 4-5-6 clutch, keeping the 4-5-6
clutch applied. The TCM supplies current to the 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 pressure
control valve 1 exhausts the 3rd, 5th, and reverse clutch,
assuring a smooth transition to sixth range.
The combined application of the 4-5-6 clutch and the 2-6
clutch produces sixth range operation.
Pressure switch 1 and pressure switch 2 remain open
(OFF) providing feedback that shift valve 1 and shift
valve 2 remain in the de-stroked position, and pressure
switch 3 remains closed (ON) providing feedback that
shift valve 3 remains in the stroked position.
If electrical power is interrupted while the transmission
is in sixth range, PCS1 and PCS2, SS3 and the torque
converter clutch (TCC) solenoid (if TCC is applied)
are de-energized. Although SS3 supplies control
main pressure to the top of shift valve 3, control main
pressure fl ows through shift valve 1 to the top of shift
valve 3, keeping the valve in the stroked position.
Normally open PCS2 exhausts PCS2 signal pressure,
allowing the pressure control valve 2 to de-stroke,
exhausting the 2-6 clutch. Normally closed PCS1 blocks
exhausting of PCS1 signal pressure, allowing PCS1
signal and PCS1 pressure to rise.
PCS1 pressure is directed through shift valve 2 to
the 3rd, 5th, and reverse clutch, applying the clutch.
Main pressure continues to fl ow through shift valve
3, shift valve 2, and the manual selector valve to the
4-5-6 clutch, keeping the 4-5-6 clutch applied. The
combination of 4-5-6 clutch and 3rd, 5th, and reverse
clutch application produces fi fth range operation for limp
home capability.
If the TCC is applied, the TCC solenoid de-energizes,
causing the TCC valve to de-stroke, exhausting
pressure form the top of the converter fl ow valve. De-
stroking the converter fl ow valve redirects main overage
pressure to “converter in” path, then to “converter out”
proceeding on to the transmission oil cooler. The TCC is
now released.
