OUTPUT RETARDER MODULE (Not released upon retarder activation to assist in charging

Available on 3000 Product Family 7-Speed the retarder cavity. The retarder housing is evacuated of
Transmissions) fluid (and the accumulator is charged) when the
retarder is not in use.
WARNING:
DO NOT USE THE RETARDER DURING
INCLEMENT WEATHER OR WHEN ROAD SUR-
FACES ARE SLIPPERY. Loss of vehicle control
may cause injury or property damage. De-energize
the retarder at the retarder enable switch. VANED STATOR HOUSING

The output retarder module (except 4000 Product VANED ROTOR

Family 7-speed models) includes the following:
VANED
• P3 carrier of the P3 planetary gear set RETARDER
HOUSING
• Output shaft assembly
• C5 clutch piston
OUTPUT
• Output speed sensor assembly SHAFT
• Output flange
The output retarder module for 4000 Product Family
7-speed models houses the following:
• Output shaft assembly
• C6 clutch piston
• Output speed sensor assembly
• Output flange
The retarder consists of the following:
• Stator
• Rotor
• Housing and a control valve body assembly
GENERAL DESCRIPTION
When installed, the retarder is an integral part of the
transmission attached to the rear of the main case (refer
to Figures 9 and 10). The retarder consists of a stator
housing, rotor, retarder housing, and retarder control
valve body. The rotor is splined to the P3 carrier and is
always driven at output shaft speed. The retarder stator
housing, rotor, and retarder housing all have integral V09456.00.00
vanes. The vaned rotor rotates between the stationary
vaned stator and vaned retarder housings.
Retardation is obtained when the retarder housing is
filled with transmission fluid and pressurized, thus
impeding rotation of the rotor and output shaft. A Figure 9. Typical 3000 Product Family
volume of fluid stored in an external accumulator is Output Retarder

Principles of Operation—May 2005 Copyright © 2005 General Motors Corp. Page 15

 RETARDER CAPACITIES
3000 and 4000 Product Families retarders are available
VANED ROTOR
in three different capacities: Low, Medium, and High.
VANED Maximum retarder capacity is determined by the TCM
STATOR VANED
HOUSING RETARDER calibration in Allison 4th Generation Controls systems.
HOUSING
3000 Product Family retarders are capable of absorbing
the following torque and horsepower:

Capacity Power Torque

OUTPUT
SHAFT 298 kw 1491 N⋅m
Low
(400 hp) (1100 lb ft)
373 kw 1763 N⋅m
Medium
(500 hp) (1300 lb ft)
447 kw 2169 N⋅m
High
(600 hp) (1600 lb ft)
4000 Product Family retarders are capable of absorbing
the following torque and horsepower output:

Capacity Power Torque

373 kw 1763 N⋅m
Low
(500 hp) (1300 lb ft)
447 kw 2169 N⋅m
Medium
(600 hp) (1600 lb ft)
447 kw 2712 N⋅m
High
(600 hp) (2000 lb ft)

RETARDER APPLY CONTROLS

WARNING:
Retarder control configurations may vary. Cer-
tain safety features are required on all Allison
transmission retarder-equipped vehicles.
• The retarder can be disabled when inclem-
ent weather or slippery road conditions are
present.
• Vehicle brake lights will always be on when
the retarder is applied.
V01084.01.00 • The retarder is automatically disengaged
when the vehicle anti-lock brake system
(ABS) is activated.
Figure 10. Typical 4000 Product Family The OEM and/or body builder is responsible for
Output Retarder providing these features.

Page 16 Copyright © 2005 General Motors Corp. Principles of Operation—May 2005

 NOTE: limited by TSC1 torque limit messages sent by certain
With Allison 4th Generation Controls, the retarder devices on the vehicle network, such as ABS. Refer to
accumulator solenoid will remain OFF when RMR Allison Transmission publication TS3989EN,
device retarder request percentage is less than Troubleshooting Manual, Appendix R, for the ERC1
20 percent. Additionally, the retarder accumulator and TSC1 messages.
solenoid will not activate when torque request is A master control is required, which permits the
less than 343 N·m (253 lb ft) for 3000 Product Fam- operator to enable or disable the retarder system
ily retarder transmissions and 374 N·m (276 lb ft) regardless of the source of retarder activation.
for the 4000 Product Family retarder transmis- J1939 Only
sions. This is intended to enhance retarder regula-
tor valve and relay valve operation at low retarder This calibration option should be selected when there
request percentages. will be no analog inputs from the RMR devices. Input
is based on messages from an SAE J1939-based
Operator control of the retarder can be accomplished vehicle controller in the form of a single ERC1
by either of the following two methods. The TCM must Retarder Selection, Non-Engine parameter, or by one
be calibrated to the proper method to be sure of desired or more TSC1 torque control messages. Retarder
retarder operation: operation may also be limited by TSC1 torque limit
• Both Analog and J1939 messages sent by certain devices on the vehicle
— Analog activation is based on a Retarder network, such as ABS. Refer to Allison Transmission
Enable switch, coupled with one or more publication TS3989EN, Troubleshooting Manual,
Allison Retarder Modulation Request (RMR) Appendix R, for the ERC1 and TSC1 messages.
components to select the desired level of A master control is required, which permits the
retardation. operator to enable or disable the retarder system
— Retardation is requested on a limited basis on regardless of the source of retarder activation.
a message from an SAE J1939-based vehicle
controllers. See paragraph below entitled ANALOG INPUT DEVICES
Both Analog and J1939.
Various types of analog retarder operator controls and
• J1939 Only vehicle interface controls are available for use with the
— Retardation is requested on a limited basis 3000 and 4000 Product Families retarders. Some of the
on messages from one or more SAE available controls include:
J1939-based vehicle controllers. See para-
graph below entitled J1939 Only. • Foot pedal
• Hand lever
Both Analog and J1939
• Automatic apply at closed throttle
When this retarder calibration option is selected, the
primary request for retardation level is based on an • Apply integrated with service brakes
analog input signal from an Allison Retarder • One-step, two-step, or three-step applies.
Modulation Request (RMR) device to the TCM. The analog retarder apply system does not actuate the
Several types of RMR devices are available for this retarder directly. The vehicle driver uses the retarder
purpose, either individually or in specific combinations operator controls to request a desired level of
as discussed in the section entitled ANALOG INPUT retardation, ranging from none, up to the maximum
DEVICES. available from the specific retarder / transmission
When the retarder system is enabled, the retarder may configuration in use. The TCM processes the request in
also be activated by an SAE J1939-based vehicle conjunction with other input data which defines the
controller in the form of a single Electronic Retarder current operating status of the transmission and
Control (ERC1) Retarder Selection, Non-Engine vehicle. The TCM turns the retarder on at the requested
parameter, or by one or more Torque Speed Control level when conditions are appropriate for retarder
(TSC1) messages. Retarder operation may also be operation.

Principles of Operation—May 2005 Copyright © 2005 General Motors Corp. Page 17

An in-depth discussion of the types and combinations of when certain conditions are met (typical percent
controls, their respective applications, and installation applies are 33 and 50).
recommendations are discussed in Allison Transmission
Combination—Almost any two of the retarder apply
Technical Document No. 175, Guidelines for Selection
systems described above can be used together in the
of Allison 4th Generation Retarder Controls. A brief
same vehicle. A combination of controls allows greater
description of each analog device follows.
flexibility in applying the retarder. Some typical
Hand Lever—The operator selects OFF or one of six combinations used are:
levels of retardation. Each successive level sends a
• Hand lever and single pressure switch—six lev-
higher voltage to the TCM and the TCM signals the
els of modulation or 100 percent apply with ser-
retarder to supply a corresponding amount of vice brake pressure.
retardation. Higher voltage to the TCM produces
• Hand lever and 3-step pressure switch—six lev-
increased retardation with maximum retardation in
els of modulation or three levels of modulation
position six.
based on service brake apply pressure.
Separate Foot Pedal (No Service Brake Apply)— • Auto apply (auto 50 percent on) and single pres-
The operator selects the amount of retardation by pedal sure switch—50 percent retarder at certain con-
position (zero to 100 percent). Maximum retardation is ditions or 100 percent apply with service brake
obtained at full pedal stroke. A voltage that is pressure.
proportional to pedal movement is sent to the TCM. • Auto apply (auto 33 percent on) and two pressure
The TCM signals the retarder to supply a switches—33 percent retarder at certain condi-
corresponding amount of retardation. Foot pedals are tions or 67 percent or 100 percent apply with ser-
available with different amounts of angular movement vice brake pressure.
to fit OEM or body builder requirements.
Pressure Switch—This option integrates retarder RETARDER ELECTRONIC CONTROLS
activation with the vehicle service brake system. One to The electronic retarder controls consist of:
three pressure switches are connected into the vehicle
• TCM
service brake system. One pressure switch could be used
to provide 100 percent retardation at a selected service • One or more resistance modules (when not using
brake pressure. A combination of two or three pressure a J1939 Only set-up)
switches could be used to give increasing levels of • Two solenoids
retardation at increasing service brake pressures.
• A retarder temperature sensor
All pressure switches are normally open and closed at a • Enable switch
certain pressure value. The closing pressure value is
stamped on the body of the pressure switch. Pressure • Service brakes
switches currently in use are 2, 4, 7, and 10 psi. All • Throttle
pressure switches are non-adjustable. • Output speed sensor
Auto Apply (Auto Full On)—This control system The TCM controls all functions of the transmission and
allows the TCM to command 100 percent retardation retarder. The resistance module converts the signal
when certain conditions are met. These conditions are: generated by the retarder apply device into a signal
• TCM has sensed that the RETARDER ENABLE which the TCM can recognize. Unless configured for
switch is ON. J1939 Only, a resistance module is required for all
analog retarder apply controls. If more than one analog
• Throttle position is below a preset value. apply control is used, a resistance module is required
• Transmission output speed is above a preset for each control device.
value.
The two retarder solenoids control the regulation of
Auto Apply (Auto Percent On)—This control system retarder cavity pressure and the application of vehicle
allows the TCM to command a percent retardation air pressure to the retarder accumulator. Both solenoids

Page 18 Copyright © 2005 General Motors Corp. Principles of Operation—May 2005

are normally closed (must be electrically energized to The ABS response may come to the TCM via a J1939
perform their function). message. In this case, the discrete input is not required.
The retarder temperature sensor sends retarder Retarder Indicator—This signal from the TCM
temperature information to the TCM. The TCM uses activates the vehicle brake lights when the retarder is
this data to: applied and may also illuminate an optional retarder
• Turn on a dash light to alert the operator when an indicator light.
over-temp condition is present. Retarder Temperature Indicator—This signal from
• Log diagnostic codes. the TCM activates an indicator light when retarder
• Reduce retarder capacity in over-temp situations. temperature has exceeded a calibration limit.
• Invoke a preselected downshift.
Retarder/Cruise Control Interactions
• Control retarder torque to requested level.
Some input functions and output functions are required Two control features affect how the retarder operates
with retarder equipped transmissions. Input functions when the vehicle is equipped with cruise control:
send a signal to the TCM. Output functions are control Feature 1: Cruise Control Retarder Auto On Disable
signals sent from the TCM. The input and output
functions used in conjunction with the retarder are: This feature applies only to electronic engines that
communicate with the transmission on either J1587 or
Input Function Output Functions J1939. The TCM calibration must specify this feature
• Retarder Enable • Retarder Indicator to be either ON or OFF.
• Service Brake Status • Retarder Temperature
If the feature is ON in the calibration, the TCM
• Anti-Lock Brake Response Indicator
prohibits retarder operation when cruise is active but
the throttle is closed, which implies a downhill coasting
Retarder Enable—A signal sent to the TCM to
operation. This feature is highly recommended if the
request retarder operation when all other conditions are
retarder-apply system automatically applies the
satisfied. This signal comes from an operator-
retarder at high levels at closed throttle.
controlled switch (usually dash-mounted). When the
switch is OFF, retarder operation is prevented. If the feature is OFF in the calibration or the engine is
Service Brake Status—A signal sent to the TCM by a not electronic, the TCM will command retarder
switch in the service brake system that indicates operation whenever the cruise control goes to zero
whether vehicle braking is being provided by the throttle. This mode of operation is only acceptable if
retarder or by the service brakes. This signal allows the the subsequent level of retarder application is less than
retarder to be applied even when a throttle position 25 percent.
sensor has failed or if the TCM has stopped receiving Feature 2: Retarder Cancel Cruise Control
throttle information from one of the vehicle data links.
A loss of throttle position information causes the TCM This feature provides for a short flash of the retarder
to default to a wide open throttle (WOT) shift schedule. indicator output whenever the requested retarder level
Retarder operation is inhibited at WOT. However, is increased. The retarder indicator output must be
when the TCM senses that the service brakes are being wired to the engine cruise control to turn off cruise
applied to slow the vehicle, the TCM allows the when the level of retardation requested is changed.
retarder to be applied. This operation emulates the effect of applying the
service brakes. Feature 2 is an optional feature that
Anti-Lock Brake Response—A signal sent to the must be specified for the controls calibration.
TCM whenever the ABS control module is active. This
input function is required on all vehicles with ABS. Assuming J1587 or J1939 engine percent load is
When the ABS is active, the TCM prevents the retarder present in cruise mode, Configurations A through D
from being applied and will not reapply until a given describe additional information about the use of
amount of time after the ABS clears. Features 1 and 2.

Principles of Operation—May 2005 Copyright © 2005 General Motors Corp. Page 19

Configuration A. If the retarder is activated by the RETARDER ACCUMULATOR
brake pedal with no auto apply: (Refer to Figures H–11 Through H–14)

• Neither Feature 1 nor Feature 2 is required. NOTE:

Configuration B. If the retarder is activated by the The terms left, right, up, and down are directions
brake pedal with auto apply: on the figures and hydraulic schematics referenced
by this description of retarder operation.
• Feature 1 keeps the retarder OFF during cruise
operation when the engine percent load goes to The accumulator is a remotely mounted, sealed,
zero. Feature 2 would have no effect because cylindrical container that contains a reserve quantity of
depressing the brake pedal will turn off cruise transmission fluid for initial fill of the retarder. The
anyway. Therefore, it doesn’t matter if Feature 2 accumulator is connected to the retarder by a Size 20
is turned ON or OFF. hose. Also connected to the accumulator is the
vehicle’s air system through an air regulator/pressure
Configuration C. If the retarder is activated by a lever,
protection valve.
it will auto apply at the appropriate level according to
the lever position when throttle reaches zero percent. Transmission fluid stored in the accumulator is
discharged into the retarder by a piston located in the
• Using Feature 1 and Feature 2—Feature 1 will accumulator. This piston is forced toward the right-side
keep the retarder OFF during cruise operation of the accumulator by air pressure only. Once the
when the engine percent load goes to zero. If retarder is deactivated, air pressure is exhausted on the
Feature 1 has already prevented the auto apply left-side of the piston and retarder pressure pushes the
and the engine percent load is still at zero, Fea- piston back to the left side of the accumulator. This
ture 2 will cause the retarder to come on and dis- recharges the accumulator until the next retarder
able cruise if the lever is moved to increase application. After the retarder flow valve shifts,
retarder capacity above a calibrated rate during a converter out pressure is aligned to the cooler circuit
cruise operation. which keeps the accumulator charged.
• Using Feature 1 without Feature 2—Feature 1
will keep the retarder OFF during cruise opera- RETARDER OPERATION
tion when the engine percent load goes to zero.
Since Feature 2 is not used, the retarder will NOTE:
never come on when cruise is active. The terms left, right, up, and down are directions
• Using Feature 2 without Feature 1—Feature 2 on the figures and hydraulic schematics referenced
can be used to cancel cruise control by increasing by this description of retarder operation.
RMR when cruise is active and percent engine
When retarder operation is requested, the following
load (throttle) is not zero percent.
sequence of events occurs (refer to Figures H–11
• Not Using Feature 1 or Feature 2—If Feature 1 is through H–14):
not used, the retarder will apply any time engine
• Retarder operation begins when PCS5 is ener-
percent load goes to zero. This will also cancel
gized.
cruise every time. Therefore Feature 2 is not
required to cancel cruise control. • Control main pressure acts on top of the retarder
control valve and retarder relay valve. Both
Configuration D. If the retarder is activated by a valves stroke downward against spring pressure.
retarder pedal:
• When the retarder relay valve moves down, main
• There is no auto-ON, therefore Feature 1 is not pressure is directed to the large retarder flow
required. Feature 2 is also not required because valve and the retarder regulator valve. Main pres-
cruise will be cancelled any time the retarder sure strokes the flow valve to the left against
pedal is used. spring pressure, aligning the retarder to the

Page 20 Copyright © 2005 General Motors Corp. Principles of Operation—May 2005

 cooler circuit. The converter flow circuit is • Main pressure is exhausted from the right side of
aligned to an auxiliary sump cooler in the vehi- large retarder flow valve. The flow valve moves
cle, if so equipped. right due to spring force acting on the left side of
the valve. This opens an exhaust path that evacu-
• When SS2 is energized, vehicle air pressure
ates the retarder cavity.
strokes the retarder accumulator piston to the
right. Oil stored in the accumulator discharges • Converter out fluid is redirected to the main
into the retarder housing, which initiates vehicle transmission oil cooler and lube circuit. Con-
retardation. verter out pressure keeps the accumulator
• The initial charge of fluid is continuously supple- charged.
mented by retarder charge pressure from the The 4000 Product Family retarders contain one
retarder regulator valve. The TCM varies current additional valve—an exhaust check valve. The function
to PCS5 to achieve the desired retarder output of the exhaust check valve is to prevent drawing fluid
torque based on calibrated capacity, request per- from the sump into the retarder cavity when the
centage, and output speed. retarder is in the OFF mode. This is specific only to
• The orifice located in the circuit at the “bottom” 4000 Product Family transmissions due to the diameter
of the regulator valve bore damps pressure fluc- of the retarder housing and the placement of the
tuations within the retarder hydraulic circuit pro- retarder valve body.
viding a stable retarder charging pressure.
TRANSFER GEAR MODULE
• The orifice located in the circuit at the “bottom”
of the relay valve bore limits retarder charge (DROPBOX) (Figure 3, Foldout 3)
pressure in the event of a “stuck open” retarder The 3000 Product Family 7-speed transmission (also
regulator valve. If the regulator valve sticks open, called the “Drop-7”) uses a transfer gear module
charge pressure would increase and approach consisting of the following:
unregulated main pressure. A feedback line
routes charge pressure to the bottom of the relay • Output adapter housing
valve.
• Transmission output shaft adapter
• The elevated charge pressure pushes the relay
valve upward. This effectively pre-regulates the • Transfer case
pressure that is supplied to the regulator valve
and limits the rise in charge pressure. Charge • Transfer case charging oil pump
pressure will stabilize at some higher pressure
point. • C6 clutch assembly
When the retarder is deactivated, the apply process is
• Drive gear assembly
reversed as follows:
• SS2 is de-energized, exhausting vehicle air pres- • Idler gear assembly
sure acting on the left side of the accumulator
piston. • Driven gear assembly

• PCS5 is briefly held ON to allow retarder pres- • Output differential planetary gear assembly
sure to refill the accumulator, then commanded
OFF at a calibrated rate. Control main pressure is • C7 clutch assembly
exhausted from the top of the retarder regulator
and relay valves. The valves stroke upward as • Transfer case scavenge pump mounted at the
spring force pushes from the bottom. right-side PTO provision

Principles of Operation—May 2005 Copyright © 2005 General Motors Corp. Page 21