Allison LCT1000 General Description

[DriVer]

Transmission General Description

The Allison LCT 1000 Transmissions are torque
converter driven, fully automatic, transmission
systems. They have up to five forward speeds,
neutral, and reverse. The fifth range has an overdrive
ratio for increased fuel economy and reduced engine
wear. These transmissions incorporate a variety of
standard and optional design features. These design
features include:
_ Direct mount to engine block
_ Flexplate drive
_ Torque converter with a torque converter clutch
(TCC) and an internal vibration damper
_ Three constant-mesh, planetary gear sets with
helical cut gears
_ Five multiple disk clutches (two rotating and
three stationary)
_ Common hydraulic system for all transmission
functions
_ Two transmission fluid filtration systems
_ Electro-hydraulic control valve assembly
_ Electronically controlled automatic gear
selection and clutch apply
_ Provision for remote transmission fluid cooler
_ Fill tube/dipstick provision on both sides of
transmission
_ Parking pawl
_ Power takeoff (PTO) provision on both sides of
transmission
_ Variety of output yokes or flanges


Electronic Component Description
Transmission Control Module
A microcomputer controls the transmission by
receiving and processing signals from various
switches and sensors. The microcomputer
determines shift sequences, shift timing, and clutch
apply and release characteristics. The microcomputer
is an independent controller and is referred to a
Transmission Control Module (TCM). TCMs are
available in 12V configurations to match the
configuration of the vehicle electrical system. The
Pressure Switch Manifold (PSM) and Park/Neutral
Position (PNP) Switch provide operator input to the
TCM. Other data sent to the TCM include throttle
position; engine, turbine, and output speeds; and
sump temperature. Any active special function, such
as anti-lock brakes or power takeoff, is also an input
to the TCM. The TCM process these data to
determine proper shift points, to monitor the current
range, to perform ratio tests, and to compile
diagnostic data. The TCM is programmed to protect
the transmission and other vehicle driveline
components by inhibiting actions such as full throttle
neutral-to-range shifts and high-speed direction
changes. The TCM determines if a system
malfunction exists and stores diagnostic codes
related to the malfunction. The codes, accessed by

the service mechanic, are used in diagnosing
persistent or intermittent trouble in the system.

Throttle Position/Torque Management
The TCM receives input on throttle position/torque
management from a signal transmitted by the engine
electronic controls. The engine electronic controls
communicate directly to the transmission electronic
controls over an SAE J 1850 or J 1939 Serial
Communication Interface (SCI) data link. The
transmission TCM must be calibrated to receive these
signals.

Speed Sensors
Important: Do not rotate the sensor in its retaining
bracket. Changing the sensor/bracket orientation may
cause improper operation. There are three speed
sensors typically required for use with 1000 series
transmissions; the engine speed sensor, the turbine
speed sensor, and the output speed sensor. The
speed sensors provide rpm information to the TCM.
The speed ratios between the various sensors allow
the TCM to determine the transmission operating
range. Speed sensor information is also used to
control the timing of clutch apply pressures, resulting
in the best possible shift quality. Hydraulic problems
are detected by comparing the speed sensor
information stored in the TCM memory. The speed
sensors are variable reluctance devices that convert
mechanical motion to an AC voltage. Each sensor
consists of a wire coil wrapped around a pole piece
that is adjacent to a permanent magnet. These
elements are contained in a housing that is mounted
adjacent to a rotating ferrous member.

Shift Selector
The vehicle is equipped with a column-type shift
selector. In addition to the column shifter provided for
the operator, another component associated with the
shift selector is the Park/Neutral Position (PNP)
switch mounted on the selector shaft. The PNP switch
transmits selector position information to the TCM.
The PNP switch mounts directly onto the transmission
housing from the outside and detects the angular
position of the shift selector shaft. This position is
communicated to the TCM so that certain vehicle
control functions can be coordinated with the position
of the shift controls. The PNP switch has redundant
circuitry to alert the TCM in the event of a single wire
or switch failure. The neutral signal output of the PNP
switch is typically used as confirmation that the
transmission is in Neutral before the engine starter is
engaged. The PNP switch is interfaced to the starter
circuit with weatherproof electrical connectors. The
reverse signal provision may be used to activate
vehicle back-up lights and/or reverse warning
devices. The shift selector and PNP switch are
customer supplied.
The operator chooses the transmission range by
moving the selector lever to the appropriate gate
position. When properly adjusted, the shifter gates
prevent inadvertent shifting between ranges, and

correspond to the internal transmission detent
positions. A positive detent is provided in the
transmission to maintain the selector shaft in the
selected position.
The TCM shift calibration determines the available
forward ranges for each selector position. Although
specific ranges vary, typical selector positions for the
1000 series are:
P – Park: Parking pawl is engaged. The transmission
is in neutral. This position is not available on all shift
selectors. When available, may be used when starting
the engine and for stationary operations.
R – Reverse: Selected to move vehicle backward
N – Neutral: May be used when starting the engine
and for stationary operations. The TCM disables the
starter switch if a range other than N (Neutral) or
P (Park) is selected before starting the vehicle.
D – Drive: The highest forward range, used for
normal driving. The transmission shifts into first range
for starting, and then automatically upshifts through
the ranges (as operating conditions permit) until the
highest range is attained.
4, (3), 2, 1 – Forward Range: There are four forward
range selector positions. The first position after N
(Neutral) is D (Drive) where all five forward ranges
are available. Another position is first range hold.
There are three choices for the next two positions.
These choices are 1–4, 1–3, and 1–2 which describe
the ranges available in that position. Workhorse
Custom Chassis chooses the two positions that best
fit the vocation for which the vehicle is intended.

Internal Components
Several components of the LCT 1000’s electrical
control system are located within the transmission as
part of the main control valve body. These components
include three types of solenoids for controlling the
hydraulic action of the valves, the pressure switch
manifold and an internal wiring harness that links the
internal components with the TCM.

Solenoids
The LCT 1000’s control valve body contains both
normally closed (N.C.) and normally open (N.O.)
solenoids. A normally closed solenoid remains closed
until a signal from the TCM energizes the solenoid. A
normally open solenoid remains open until the TCM
energizes the solenoid. When a solenoid valve is in
the closed position, the valve blocks flow. When a
solenoid valve is in the open position, flow is
permitted through the valve. The pulse width
modulated F and the ON/OFF shift valve solenoids C,
D, and E, are normally closed (N.C.). Both solenoid
types have an orifice, electrical windings, an iron
core, and a steel check ball. The solenoids used in
the 1000 Series differ in their ability to control flow or
fluid pressure. The solenoids may operate in the open
or closed state with no modulation capacity (C, D, and
E solenoids), an intermediate flow and resultant
pressure based on duty cycle (F solenoid) or produce
pressure proportional to current (A and B solenoids).

Shift solenoids C, D, and E provide the necessary
logic to distribute fluid 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, C, D, and E. 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 pressure
switch manifold) which provides feedback to the
computer as to the valve’s position.
Trim solenoids A and B are used to control oncoming,
off-going, and holding pressure to the five clutches.
These solenoids are referred to as Pressure
Proportional to Current (PPC) solenoids since the
output hydraulic pressure supplied by these solenoids
is proportional to the controlled current command.

Pressure Switch Manifold
The pressure switch manifold (PSM) is a
multiple-switch assembly made up of three normally
open pressure switches and one normally closed
switch.
Normally open switches correspond to shift valves C,
D, and E. Fluid pressures are fed from shift valves C,
D, and E and the manual selector valve to the
switches based on the positions of the valves and
shift selector. The shift valve fluid pressures reflect
the logic condition at the corresponding solenoids.
This logic indicates the current transmission operating
range to the TCM.
The three fluid pressure switches corresponding to
the shift valves are normally open (contacts not
touching) when no fluid pressure is present, so that
electrical current is stopped at that switch. When fluid
pressure is routed to the switch, it moves the
diaphragm and upper contact so that the contact
element touches both the positive and the ground
contacts. This closes the circuit and allows current to
flow from the positive contact through a switch.
The pressure switch corresponding to reverse is
normally closed, since fluid pressure is always
present unless the selector valve is moved to
Reverse. The PSM also contains a temperature
sensor thermistor for sump temperature. Changes in
sump fluid temperature are indicated by changes in
sensor resistance (for example, increasing
temperature causes decreased sensor resistance).
The resistance value is then relayed to the TCM as
an input for shift control.

Internal Wiring Harness
The internal wiring harness has connectors for the
shift solenoids C, D, and E. Connectors go to clutch
trim solenoids A and B. A connector goes to the
torque converter clutch solenoid (F). There is also a
connector for the pressure switch manifold. All of
these connectors go to the main electrical connector.
The transmission main electrical connector transports
signals from these connectors to the TCM via the
external harness.