WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
85
2007 W Series Chassis
WSM082106
Reverse
When the manual selector valve is moved from Neutral
(N) to Reverse (R), shift solenoid 1 (SS1) de-energizes,
turning OFF pressure switch 1. SS2 and SS3 remain
energized, keeping pressure switch 2 and pressure
switch 3 on. Reverse signal pressure is exhausted,
removing pressure from pressure switch 4, turning on
the normally closed pressure switch 4.
The transmission control module (TCM) energizes
pressure control solenoid 2 (PCS2) to control the rate at
which PCS2 pressure supplies oil to the oncoming 3rd,
5th, and reverse clutch, assuring a smooth transition to
reverse. As PCS2 is energized, PCS2 signal pressure
increases. Initially, the pressure control valve 2 gain
valve spring keeps the gain valve away from pressure
control valve 2, so that only PCS2 signal pressure acts
on pressure control valve 2. As PCS2 signal pressure
increases, the PCS2 pressure increases. The PCS2
signal pressure also acts on the gain valve, stroking the
valve and compressing the gain valve spring. When the
gain valve spring is compressed suffi ciently, the gain
valve contacts pressure control valve 2. The gain valve
spring allows the 3rd, 5th, and reverse clutch initial apply
to be controlled at a lower gain rate, improving control
of the oncoming 3rd, 5th, and reverse clutch. Once the
gain valve makes contact with pressure control valve 2,
PCS2 pressure increases at a higher gain rate, PCS2
pressure fl ows through shift valve 1 to shift valve 3 and
on to apply the 3rd, 5th, and reverse clutch. When the
shift to reverse is complete, PCS2 fully energizes and
PCS2 pressure fully applies the 3rd, 5th, and reverse
clutch. PCS1 supplies full pressure to the low and
reverse clutch.
The application of the 3rd, 5th, and reverse clutch and
the low and reverse clutch produces reverse range
operation.
If electrical power is interrupted with the transmission
operating in reverse range, PCS2, SS2, and SS3 de-
energize. When PCS2 de-energizes, the normally open
solenoid exhausts PCS2 signal pressure, causing
pressure control valve 2 to de-stroke, exhausting and
releasing the 3rd, 5th, and reverse clutch. Shift valve 1
remains in the stroked position. Control main pressure
goes through shift valve 1 to the top of shift valve 3
keeping shift valve 3 stroked. Normally closed PCS1
blocks the exhaust of PCS1 signal pressure, and PCS1
pressure is maintained. PCS1 pressure continues to be
directed through shift valve 2, which stays down due to
the “latching” effect of pressure on two different diameter
lands, to the low and reverse clutch, keeping the low
and reverse clutch applied. Because only one clutch is
applied, the transmission shifts to neutral range.
If electrical power is interrupted with the transmission
operating in reverse range, resulting in neutral
operation, main pressure is directed through shift valve
3 to shift valve 2. Because shift valve 2 stays stroked
due to the “latching” effect of pressure on two different
diameter lands, main pressure is blocked from reaching
the manual selector valve. If the manual selector
valve is moved to Neutral (N) or a forward range, the
