WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
62
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
Solenoids
The 1000 Series control valve body contains both
normally closed (N/C) and normally open (N/O)
solenoids. A N/C solenoid remains closed until a signal
from the TCM energizes the solenoid. A N/O solenoid
remains open until the TCM energizes the solenoid.
When a solenoid valve is in the closed position, the
valve blocks the fl ow. When a solenoid valve is in the
open position, fl ow is permitted through the valve. Shift
solenoid 1 (SS1) (4), shift solenoid 2 (SS2) (2) and shift
solenoid 3 (SS3) (3) are N/C. Both solenoid types have
an orifi ce, electrical windings, an iron core, and a steel
check ball.
Shift solenoids provide the necessary logic to distribute
fl uid to the correct clutches. The shift solenoids provide
either full control main pressure or exhaust to the
head of each of the corresponding shift valves. Since
the valve states, stroked or unstroked, are critical to
providing the correct transmission range, each shift
valve has a pressure switch, located in the PSM, which
provides feedback to the computer regarding the
position of the valve.
Modulated main pressure solenoid (7) is a N/C
solenoid used to modulate the transmission main
pressure. Under specifi c conditions, such as low throttle
setting, low engine torque, low engine speed, and low
transmission output speeds, the TCM commands the
solenoid ON. When the solenoid is applied, fl uid is
routed to the main pressure regulator valve; this in turn
reduces the main pressure schedule and improves the
volume of oil through the overage circuit. By modulating
main pressure, the cooler fl ow at idle can be increased,
allowing improved cooling and reducing transmission
pump noise.
Pressure control solenoid 1 (PCS1) (6), pressure control
solenoid 2 (PCS2) (4), and the torque converter clutch
(TCC) (1) are used to control on-coming, off-going, and
holding pressure to the 5 clutches and the TCC. These
solenoids are referred to as variable bleed solenoids,
since the output hydraulic pressure supplied by these
solenoids is proportional to the controlled current
command.
