WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
90
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
Default Forward - 3rd Range Limp Home
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
closed PCS1 continues to block the exhaust of the
PCS1 signal pressure (signal remains control main).
The signal pressure on top of pressure control valve
1 produces maximum PCS1 pressure, which is routed
through shift valve 2 to the 3rd, 5th, and reverse clutch,
keeping the clutch applied. With the manual selector
valve in a forward position, main pressure continues
to feed the 1-2-3-4 clutch 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 keeps
the transmission in third range for limp home capability.
If the TCC is applied, the TCC solenoid de-energizes,
causing 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
overage to converter in and converter out to the cooler.
The TCC is now released.
