Allison transmission at 545 Repair Workshop Service Manual

Printed in the U.S.A. Copyright © 1996 General Motors Corp.
Service
Manual
Allison Transmission
SM1241EN
AUTOMATIC MODELS
AT 540,
AT 542(N)(R)(NFE),
AT 543,
AT 545(N)(R),
AT 1542P,
AT 1545P(N)
FEBRUARY 1996
Revision 1, 1999 April
Division of General Motors Corporation
P.O. Box 894 Indianapolis, Indiana 46206-0894

ii Copyright © 1996 General Motors Corp.
ALLISON TRANSMISSION AUTOMATIC AT SERIES TRANSMISSIONS
TRADEMARK USE
The following trademarks are the property of the companies indicated:
• DEXRON® is a registered trademark of General Motors Corporation.
• Biobor® JF is the registered trademark for a biological inhibitor manufactured by U.S. Borax
and Chemical Corporation.
• Teﬂon® is a registered trademark of the DuPont Corporation.
• Loctite® is a registered trademark of the Loctite Corporation.
NOTE:
This publication is revised periodically to include improvements,
new models, special tools, and procedures. A revision is indicated
by letter suffix to the publication number. Check with your Allison
Transmission service outlet for the currently applicable publica-
tion. Additional copies of this publication may be purchased from
authorized Allison Transmission service outlets. Look in your
telephone directory under the heading of Transmissions — Truck,
Tractor, etc.

WARNINGS, CAUTIONS, AND NOTES
Three types of headings are used in this manual to attract your attention:
NOTE:
is used when an operating procedure, practice, etc.,
is essential to highlight.
WARNING!
is used when an operating procedure, practice,
etc., which, if not correctly followed, could result
in personal injury or loss of life.
CAUTION:
is used when an operating procedure, practice,
etc., which, if not strictly observed, could result
in damage to or destruction of equipment.
Copyright © 1996 General Motors Corp. iii
IT IS YOUR RESPONSIBILITY to be completely familiar with the Warnings and Cau-
tions described in this Service Manual. These Warnings and Cautions advise against the
use of specific service methods that can result in personal injury, damage to the equip-
ment, or cause the equipment to become unsafe. It is, however, important to understand
that these Warnings and Cautions are not exhaustive. Allison Transmission could not
possibly know, evaluate, and advise the service trade of all conceivable ways in which
service might be done or of the possible hazardous consequences of each way. Conse-
quently, Allison Transmission has not undertaken any such broad evaluation. Accord-
ingly, ANYONE WHO USES A SERVICE PROCEDURE OR TOOL WHICH IS NOT
RECOMMENDED BY ALLISON TRANSMISSION MUST first be thoroughly satisfied
that neither personal safety nor equipment safety will be jeopardized by the service
methods selected.
Proper service and repair are important to the safe, reliable operation of the equipment.
The service procedures recommended by Allison Transmission and described in this Ser-
vice Manual are effective methods for performing service operations. Some of these ser-
vice operations require the use of tools specifically designed for the purpose. The special
tools should be used when and as recommended.
IMPORTANT SAFETY NOTICE

iv Copyright © 1996 General Motors Corp.
LIST OF WARNINGS
This manual contains the following warnings —
IT IS YOUR RESPONSIBILITY TO BE FAMILIAR WITH ALL OF THEM.
• When checking the transmission fluid level, be sure that the parking brake
and/or emergency brakes are set and properly engaged, and the wheels are
blocked. Unexpected and possible sudden movement may occur if these
precautions are not taken.
• While conducting a stall check, the vehicle must be positively prevented from
moving. Apply the parking brake and service brake, and block the wheels
securely. Warn personnel to keep clear of the vehicle and its travel path.
Failure to do so can cause serious injury.
• Observe safety precautions during hydraulic pressure check procedures. All
personnel must stand clear of the vehicle. Take precautions against movement
of the vehicle. Be sure that gauges (vacuum, pressure, tachometer) have
extended lines so that they can be read from inside the vehicle.
• Do not burn discarded Teflon® seals; toxic gases are produced by burning.
• Never dry bearings with compressed air. A spinning bearing can disintegrate
allowing balls or rollers to become lethal flying projectiles. Also, spinning a
bearing without lubrication can damage the bearing.
• Be sure all pressure is exhausted from the torque converter before loosening
the test fixture nut and removing the test fixture.
• The retarder control priority valve and plug and regulator valve and plug are
spring-loaded and must be restrained while the retaining pins are being
removed.
• The retarder control autoflow valve plug is spring-loaded and must be
restrained while the snapring is being removed.

Copyright © 1996 General Motors Corp. v
Paragraph Page Paragraph Page
TABLE OF CONTENTS
Section 1. GENERAL INFORMATION
1–1. SCOPE OF MANUAL
a. Coverage. . . . . . . . . . . . . . . . . . . . . . . . . .1–1
b. Illustrations . . . . . . . . . . . . . . . . . . . . . . . .1–1
c. Maintenance Information . . . . . . . . . . . . .1–1
1–2. SUPPLEMENTARY INFORMATION . . . .1–1
1–3. ORDERING PARTS
a. Transmission Nameplate . . . . . . . . . . . . .1–1
b. Parts Catalog. . . . . . . . . . . . . . . . . . . . . . .1–1
1–4. GENERAL DESCRIPTION
a. Automatic, Four Speeds . . . . . . . . . . . . . .1–4
b. Torque Converter and Lockup Clutch . . .1–4
c. Planetary Gearing, Clutches. . . . . . . . . . .1–4
d. Main Control Valve Body . . . . . . . . . . . .1–4
1–5. OPERATING INSTRUCTIONS. . . . . . . . . .1–4
1–6. SPECIFICATIONS AND DATA . . . . . . . . .1–4
Section 2. DESCRIPTION AND OPERATION
2–1. SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2–1
2–2. MOUNTING
a. To Engine . . . . . . . . . . . . . . . . . . . . . . . . .2–1
b. To Vehicle . . . . . . . . . . . . . . . . . . . . . . . .2–1
2–3. INPUT DRIVE. . . . . . . . . . . . . . . . . . . . . . . .2–1
2–4. TRANSMISSION HOUSING. . . . . . . . . . . .2–1
2–5. TORQUE CONVERTER ASSEMBLY
AND LOCKUP CLUTCH
a. Description . . . . . . . . . . . . . . . . . . . . . . . .2–1
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . .2–1
2–6. OIL PUMP ASSEMBLY
a. Description . . . . . . . . . . . . . . . . . . . . . . . .2–2
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . .2–2
2–7. FORWARD CLUTCH AND
TURBINE SHAFT
a. Description . . . . . . . . . . . . . . . . . . . . . . . .2–2
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . .2–2
2–8. FOURTH CLUTCH
a. Description . . . . . . . . . . . . . . . . . . . . . . . .2–3
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . .2–3
2–9. SECOND AND THIRD CLUTCH AND
CENTER SUPPORT
a. Description . . . . . . . . . . . . . . . . . . . . . . . .2–3
b. Operation of Third Clutch . . . . . . . . . . . .2–3
c. Operation of Second Clutch . . . . . . . . . . .2–4
2–10. FIRST CLUTCH
a. Description . . . . . . . . . . . . . . . . . . . . . . . 2–4
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . 2–4
2–11 PLANETARY GEAR UNIT
a. Description . . . . . . . . . . . . . . . . . . . . . . . 2–4
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . 2–4
2–12. SPEEDOMETER DRIVE/SPEED
SENSOR WHEEL
a. Description . . . . . . . . . . . . . . . . . . . . . . . 2–5
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . 2–5
2–13. GOVERNOR
a. Description . . . . . . . . . . . . . . . . . . . . . . . 2–5
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . 2–5
2–14. MODULATOR
a. Vacuum Modulator. . . . . . . . . . . . . . . . . 2–5
b. Mechanical Modulator . . . . . . . . . . . . . . 2–5
c. Electric Modulator . . . . . . . . . . . . . . . . . 2–5
2–15. OIL PAN AND FILTER
a. Description . . . . . . . . . . . . . . . . . . . . . . . 2–6
b. Function . . . . . . . . . . . . . . . . . . . . . . . . . 2–6
2–16. HYDRAULIC RETARDER
a. Description . . . . . . . . . . . . . . . . . . . . . . . 2–6
b. Operation . . . . . . . . . . . . . . . . . . . . . . . . 2–6
2–17. MAIN CONTROL VALVE ASSEMBLY . . 2–7
2–18. HYDRAULIC SYSTEM
a. System Functions . . . . . . . . . . . . . . . . . . 2–7
b. System Schematic. . . . . . . . . . . . . . . . . . 2–7
c. Filter, Pump Circuit . . . . . . . . . . . . . . . . 2–7
d. Main-Pressure Circuit (Red). . . . . . . . . . 2–7
e. Converter-In (Yellow), Converter-Out
(Orange), Lubrication (Green) Circuits . . 2–8
f. Selector Valve, Neutral, Forward
Regulator Circuit (Orange and Yellow) . . 2–8
g. Governor Valve, Governor Circuit
(Green and White) . . . . . . . . . . . . . . . . . 2–8
h. Modulator Pressure Circuit
(Red and Green) . . . . . . . . . . . . . . . . . . . 2–8
i. Clutch Circuits . . . . . . . . . . . . . . . . . . . . 2–9
j. Hold Regulator Valve. . . . . . . . . . . . . . . 2–9
k. Automatic Upshifts. . . . . . . . . . . . . . . . . 2–9
l. Automatic Downshifts . . . . . . . . . . . . . . 2–9
m. Downshift Inhibiting. . . . . . . . . . . . . . . . 2–9
n. Trimmer Valves . . . . . . . . . . . . . . . . . . 2–10
o. Priority Valve . . . . . . . . . . . . . . . . . . . . 2–10
p. Trimmer Regulator Valve. . . . . . . . . . . 2–10

vi Copyright © 1996 General Motors Corp.
AT 500, 1500 SERIES AUTOMATIC TRANSMISSIONS
2–19. TORQUE PATHS THROUGH
TRANSMISSION
a. Converter Operation . . . . . . . . . . . . . . . .2–11
b. Neutral Operation . . . . . . . . . . . . . . . . . .2–11
c. First-Range Operation . . . . . . . . . . . . . .2–12
d. Second-Range Operation . . . . . . . . . . . .2–13
e. Third-Range Operation. . . . . . . . . . . . . .2–14
f. ConverterOperation(AT1500SeriesModels)
2–14
g. Lockup Operation
(AT 1500 Series Models) . . . . . . . . . . . .2–14
h. Fourth-Range Operation. . . . . . . . . . . . .2–15
i. Fourth-Range Lockup Operation
(AT 1500 Series Models) . . . . . . . . . . . .2–15
j. Reverse Operation . . . . . . . . . . . . . . . . .2–16
Section 3. PREVENTIVE MAINTENANCE
3–1. SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3–1
3–2. PERIODIC INSPECTION AND CARE . . . 3–1
3–3. IMPORTANCE OF PROPER
TRANSMISSION FLUID LEVEL
a. Effects of Improper Fluid Level. . . . . . . .3–1
b. Foaming and Aerating . . . . . . . . . . . . . . .3–1
3–4. DIPSTICK MARKINGS . . . . . . . . . . . . . . . .3–1
3–5. TRANSMISSION FLUID LEVEL
CHECK PROCEDURE
a. Preparation . . . . . . . . . . . . . . . . . . . . . . . .3–2
b. Cold Check . . . . . . . . . . . . . . . . . . . . . . . .3–3
c. Hot Check. . . . . . . . . . . . . . . . . . . . . . . . .3–3
3–6. KEEPING TRANSMISSION
FLUID CLEAN . . . . . . . . . . . . . . . . . . . . . . .3–3
3–7. TRANSMISSION FLUID
RECOMMENDATIONS
a. Recommended Automatic Transmission
Fluid and Viscosity Grade . . . . . . . . . . . .3–3
3–8. TRANSMISSION FLUID AND FILTER
CHANGE INTERVALS . . . . . . . . . . . . . . . .3–4
3–9. TRANSMISSION FLUID
CONTAMINATION
a. Examine at Fluid Change . . . . . . . . . . . . .3–4
b. Metal Particles . . . . . . . . . . . . . . . . . . . . .3–4
c. Coolant Leakage. . . . . . . . . . . . . . . . . . . .3–4
d. Auxiliary Filter . . . . . . . . . . . . . . . . . . . . .3–4
3–10. TRANSMISSION FLUID AND FILTER
CHANGE PROCEDURES
a. Disassembly . . . . . . . . . . . . . . . . . . . . . . 3–7
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . . 3–7
3–11. BREATHER. . . . . . . . . . . . . . . . . . . . . . . . . 3–8
3–12. LINKAGE
a. Shift Selector Lever and Control
Linkage . . . . . . . . . . . . . . . . . . . . . . . . . . 3–9
b. Mechanical Actuator Adjustment. . . . . . 3–9
c. Other Linkage Adjustments . . . . . . . . . . 3–9
3–13. ADJUSTMENT OF SHIFT POINTS
a. Calibrated on Test Stand or in Vehicle. . . 3–9
b. Location of Adjusting Components . . . . 3–9
c. Checks Before Adjusting Shift Points . . 3–10
d. Calibration by Road Test Method . . . . 3–10
e. CalibrationbySpeedometerReadingsMethod
3–10
f. Calibration by Test Stand Method . . . . 3–10
3–14. TRANSMISSION STALL TEST AND
NEUTRAL COOL-DOWN CHECK
a. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 3–15
b. Stall Testing Preparation . . . . . . . . . . . 3–15
c. Stall Test Procedures — Vehicles
Without Smoke-Controlled Engines . . 3–15
d. Stall Test Procedures — Vehicles
With Smoke-Controlled Engines . . . . . 3–16
e. Neutral Cool-Down Check Procedure. . . 3–16
f. Results. . . . . . . . . . . . . . . . . . . . . . . . . . 3–16
3–15. PRESERVATION AND STORAGE
a. Storage, New Transmissions . . . . . . . . 3–16
b. Preservation Methods . . . . . . . . . . . . . . 3–16
c. Storage, One Year — Without
Transmission Fluid . . . . . . . . . . . . . . . . 3–16
d. Storage, One Year — With
Transmission Fluid . . . . . . . . . . . . . . . . 3–17
e. Restoring Transmission to Service. . . . 3–17
3–16. REPLACEMENT OF COMPONENTS
WHILE TRANSMISSION IS IN THE
VEHICLE CHASSIS
a. Replacement of Selector Shaft Seal . . . 3–18
b. Removal of Output Flange,
Output Seal . . . . . . . . . . . . . . . . . . . . . . 3–18
c. Removal of Output Shaft Bearing . . . . 3–18
d. Removal of Speedometer Drive
Gear or Speed Sensor Wheel and
Selective Spacer . . . . . . . . . . . . . . . . . . 3–18

Copyright © 1996 General Motors Corp. vii
Paragraph PageParagraph Page
3–16. REPLACEMENT OF COMPONENTS
WHILE TRANSMISSION IS IN THE
VEHICLE CHASSIS (cont’d)
e. Installation of Speedometer Drive
Gear or Speed Sensor Wheel and
Selective Spacer . . . . . . . . . . . . . . . . . . .3–18
f. Installation of Output Shaft Bearing
and Snapring. . . . . . . . . . . . . . . . . . . . . .3–19
g. Installation of Output Seal . . . . . . . . . . .3–19
h. Installation of Output Flange . . . . . . . . .3–19
3–17. TROUBLESHOOTING — BEFORE
REMOVAL OR OPERATION OF
TRANSMISSION
a. Visual Inspection . . . . . . . . . . . . . . . . . .3–19
b. Vacuum Modulator Check . . . . . . . . . . .3–19
3–18. TROUBLESHOOTING — BEFORE
REMOVAL AND DURING OPERATION
a. Determine Cause of Trouble . . . . . . . . .3–21
b. Proper Engine Tuning. . . . . . . . . . . . . . .3–21
c. Hydraulic Pressure Checking
Procedures. . . . . . . . . . . . . . . . . . . . . . . .3–21
3–19. TROUBLESHOOTING — TRANSMISSION
REMOVED FROM VEHICLE . . . . . . . . . .3–21
3–20. TROUBLESHOOTING PROCEDURES. . .3–21
Section 4. GENERAL OVERHAUL
INFORMATION
4–1. SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4–1
4–2. TOOLS AND EQUIPMENT
a. Improvised Tools and Equipment . . . . . .4–1
b. Special Tools . . . . . . . . . . . . . . . . . . . . . .4–1
c. Mechanic’s Tools, Shop Equipment . . . .4–8
4–3. REPLACEMENT PARTS
a. Ordering Information . . . . . . . . . . . . . . . .4–9
b. Parts Normally Replaced . . . . . . . . . . . . .4–9
4–4. CAREFUL HANDLING . . . . . . . . . . . . . . . .4–9
4–5. CLEANING, INSPECTION
a. Dirt-Free Assembly . . . . . . . . . . . . . . . . .4–9
b. Cleaning Parts. . . . . . . . . . . . . . . . . . . . . .4–9
c. Cleaning Bearings. . . . . . . . . . . . . . . . . . .4–9
d. Inspecting Bearings . . . . . . . . . . . . . . . .4–10
e. Keeping Bearings Clean. . . . . . . . . . . . .4–10
f. Inspecting Cast Parts,
Machined Surfaces . . . . . . . . . . . . . . . . .4–10
g. Inspecting Bushings, Thrust Washers . . 4–11
h. Inspecting Oil Seals, Gaskets . . . . . . . . 4–11
i. Inspecting Gears . . . . . . . . . . . . . . . . . . 4–12
j. Inspecting Splined Parts . . . . . . . . . . . . 4–12
k. Inspecting Threaded Parts. . . . . . . . . . . 4–12
l. Inspecting Snaprings . . . . . . . . . . . . . . 4–12
m. Inspecting Springs . . . . . . . . . . . . . . . . 4–12
n. Inspecting Clutch Plates . . . . . . . . . . . . 4–12
o. Inspecting Swaged, Interference-Fit
Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–12
p. Inspecting Balls in Clutch Housings . . 4–12
q. Inspecting Seal Contact Surfaces . . . . . 4–12
4–6. ASSEMBLY PROCEDURES
a. Clutches, Pistons. . . . . . . . . . . . . . . . . . 4–13
b. Parts Lubrication. . . . . . . . . . . . . . . . . . 4–13
c. External Pipe Plugs, Hydraulic
Fittings . . . . . . . . . . . . . . . . . . . . . . . . . 4–13
d. Oil-Soluble Grease . . . . . . . . . . . . . . . . 4–13
e. Lip-Type Seals (Metal Encased) . . . . . 4–13
f. Interference-Fit Parts . . . . . . . . . . . . . . 4–13
g. Sleeve-Type Bearings and Bushings . . 4–13
h. Bearings (Ball or Roller). . . . . . . . . . . . 4–13
4–7. REMOVING (OR INSTALLING)
TRANSMISSION
a. Drain Transmission Fluid. . . . . . . . . . . 4–14
b. Check Linkages and Lines . . . . . . . . . . 4–14
c. Remove, Clean Transmission. . . . . . . . 4–14
d. Transmission Installation.. . . . . . . . . . . 4–14
4–8. WEAR LIMITS . . . . . . . . . . . . . . . . . . . . . 4–14
4–9. SPRING SPECIFICATIONS. . . . . . . . . . . 4–14
4–10. TORQUE SPECIFICATIONS. . . . . . . . . . 4–14
Section 5. DISASSEMBLY OF
TRANSMISSION
5–1. SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5–1
5–2. GENERAL INFORMATION
a. General Information . . . . . . . . . . . . . . . 5–1
b. Removal of Exterior Hoses and Lines . . 5–1
5–3. TRANSMISSION DISASSEMBLY
a. Mounting of Transmission in
Table-Mounted Holding Fixture . . . . . . 5–1
b. Removal of Torque Converter . . . . . . . . 5–2
c. Removal of Vacuum Modulator,
Mechanical Actuator. . . . . . . . . . . . . . . . 5–2

viii Copyright © 1996 General Motors Corp.
5–3. TRANSMISSION DISASSEMBLY (cont’d)
d. Removal of Breather. . . . . . . . . . . . . . . . .5–2
e. Removal of Governor. . . . . . . . . . . . . . . .5–3
f. Removal of Oil Pan . . . . . . . . . . . . . . . . .5–3
g. Removal of Filter . . . . . . . . . . . . . . . . . . .5–3
h. Removal of Main Control Valve Body . . .5–3
i. Removal of Pump. . . . . . . . . . . . . . . . . . .5–5
j. Removal of Forward Clutch and
Turbine Shaft . . . . . . . . . . . . . . . . . . . . . .5–6
k. Removal of Retarder Components,
Forward Clutch and Turbine Shaft. . . . . .5–6
l. Removal of Fourth Clutch . . . . . . . . . . . .5–7
m. Removal of Third Clutch . . . . . . . . . . . . .5–7
n. Removal of Center Support Assembly. . .5–7
o. Removal of Planetary Gearing . . . . . . . . .5–8
p. Removal of Second Clutch. . . . . . . . . . . .5–9
q. Removal of First Clutch . . . . . . . . . . . . . .5–9
r. Removal of Output Shaft Seal
and Bearing. . . . . . . . . . . . . . . . . . . . . . .5–10
Section 6. REBUILD OF SUBASSEMBLIES
6–1. SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6–1
6–2. GENERAL INFORMATION FOR
SUBASSEMBLY REBUILD . . . . . . . . . . . .6–1
6–3. INSPECTING AND TESTING TORQUE
CONVERTER
a. Preliminary Inspection . . . . . . . . . . . . . . .6–1
b. End Play Check . . . . . . . . . . . . . . . . . . . .6–1
c. Leak Check. . . . . . . . . . . . . . . . . . . . . . . .6–2
d. Inspection of Hub . . . . . . . . . . . . . . . . . . .6–2
e. Preparation for Reuse of Converter . . . . .6–2
6–4. TORQUE CONVERTER
ASSEMBLY — AT 543 MODELS
a. Preliminary Check of End Play . . . . . . . .6–2
b. Disassembly . . . . . . . . . . . . . . . . . . . . . . .6–2
c. Replacement of Needle Bearing
Assembly in Stator Assembly . . . . . . . . .6–4
d. Assembly . . . . . . . . . . . . . . . . . . . . . . . . .6–4
6–5. GOVERNOR
a. Disassembly . . . . . . . . . . . . . . . . . . . . . . .6–7
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . . .6–8
6–6. MAIN CONTROL VALVE BODY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . . .6–8
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . .6–10
6–7. RETARDER CONTROL VALVE BODY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–12
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–13
6–8. TRANSFER PLATE ASSEMBLY
(Retarder Models)
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–13
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–14
6–9. OIL PUMP AND FRONT
SUPPORT ASSEMBLY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–14
b. Installation of Stator Shaft
and Bushing . . . . . . . . . . . . . . . . . . . . . 6–16
c. Pump Gear Clearance Check.. . . . . . . . 6–17
d. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–18
6–10. FORWARD CLUTCH AND TURBINE
SHAFT ASSEMBLY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–20
b. Checking Clutch Pack Clearance
(Models Without Wave Plate) . . . . . . . 6–22
c. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–23
6–11. RETARDER HOUSING ASSEMBLY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–25
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–25
6–12. FOURTH CLUTCH ASSEMBLY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–25
b. Checking Clutch Pack Clearance . . . . . 6–26
c. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–27
6–13. CENTER SUPPORT ASSEMBLY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–27
b. Rework of Center Support
Piston Retainer Locating Notches . . . . 6–28
c. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–28
6–14. PLANETARY GEAR UNIT
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–29
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–30
6–15. TRANSMISSION MAIN HOUSING
ASSEMBLY
a. Disassembly . . . . . . . . . . . . . . . . . . . . . 6–32
b. Assembly . . . . . . . . . . . . . . . . . . . . . . . 6–33
6–16. PLANETARY CARRIER ASSEMBLIES
a. Inspection . . . . . . . . . . . . . . . . . . . . . . . 6–34
b. Removal of Pinion Components. . . . . . 6–35
c. Replacing Bushing in Front Planetary Carrier
6–35
d. Installation of Pinion Components. . . . 6–36

Copyright © 1996 General Motors Corp. ix
Paragraph PageParagraph Page
6–17. CLUTCH STACK MEASUREMENT
a. Assembly Line . . . . . . . . . . . . . . . . . . . .6–37
b. Forward Clutch. . . . . . . . . . . . . . . . . . . .6–37
c. Fourth Clutch . . . . . . . . . . . . . . . . . . . . 6–37
d. Third Clutch . . . . . . . . . . . . . . . . . . . . . .6–38
e. Second Clutch. . . . . . . . . . . . . . . . . . . . .6–38
f. First Clutch . . . . . . . . . . . . . . . . . . . . . . 6–39
Section 7. ASSEMBLY OF TRANSMISSION
7–1. SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7–1
7–2. GENERALINFORMATIONFORFINALASSEMBLY
7–1
7–3. SELECTIVE COMPONENTS
a. Establish Clearances. . . . . . . . . . . . . . . . .7–1
b. Clutch Plate Stack Measurements . . . . . .7–1
7–4. INSTALLATION OF FIRST CLUTCH
AND GEARING
a. First Clutch . . . . . . . . . . . . . . . . . . . . . . . .7–1
b. First Clutch Running Clearance . . . . . . . .7–2
c. Planetary Gear Unit . . . . . . . . . . . . . . . . .7–4
7–5. INSTALLATION OF SECOND CLUTCH
AND CENTER SUPPORT
a. Second Clutch Pack . . . . . . . . . . . . . . . . .7–4
b. Center Support and Pistons . . . . . . . . . . .7–5
7–6. INSTALLATION OF REAR BEARING
SPACER AND FOURTH CLUTCH
a. Selecting, Installing Rear Bearing
Spacer . . . . . . . . . . . . . . . . . . . . . . . . . . . .7–6
b. Fourth Clutch . . . . . . . . . . . . . . . . . . . . . .7–8
7–7. INSTALLATION OF THIRD AND
FORWARD CLUTCHES
a. Third Clutch . . . . . . . . . . . . . . . . . . . . . . .7–9
b. Retarder Housing Assembly. . . . . . . . . . .7–9
c. Forward Clutch and Turbine Shaft
Assembly . . . . . . . . . . . . . . . . . . . . . . . .7–10
7–8. INSTALLATION OF OIL PUMP
ASSEMBLY
a. Selection of Front Thrust Washer . . . . .7–11
b. Pump Assembly . . . . . . . . . . . . . . . . . . .7–12
7–9. INSTALLATION OF OUTPUT
SHAFT OIL SEAL. . . . . . . . . . . . . . . . . . . .7–13
7–10. INSTALLATION OF MAIN CONTROL
VALVE BODY, OIL FILTER, AND
OIL PAN
a. Main Control Valve Body . . . . . . . . . . 7–13
b. Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–15
c. Oil Pan . . . . . . . . . . . . . . . . . . . . . . . . . 7–15
7–11. INSTALLATION OF GOVERNOR,
MODULATOR, AND TORQUE
CONVERTER
a. Governor. . . . . . . . . . . . . . . . . . . . . . . . 7–16
b. Vacuum Modulator. . . . . . . . . . . . . . . . 7–16
c. Torque Converter Assembly. . . . . . . . . 7–17
7–12. REMOVAL OF TRANSMISSION
FROM OVERHAUL STAND AND
INSTALLATION OF EXTERNAL
COMPONENTS
a. Supporting Transmission . . . . . . . . . . . 7–18
b. Determining Third Clutch Clearance . . 7–18
c. Installing Retarder Valve Body . . . . . . 7–18
d. Installing PTO Cover . . . . . . . . . . . . . . 7–18
e. Installing Neutral Start Switch,
Speedometer Components . . . . . . . . . . 7–18
f. Shift Lever Installation. . . . . . . . . . . . . 7–18
7–13. CHECKING AND ADJUSTING
SHIFT POINTS . . . . . . . . . . . . . . . . . . . . . 7–19
7–14. POWER TAKEOFF COMPONENTS
(Models Without Retarder)
a. Existing Installation . . . . . . . . . . . . . . . 7–19
b. Determining Turbine-Driven PTO
Backlash . . . . . . . . . . . . . . . . . . . . . . . . 7–19
c. New Installation . . . . . . . . . . . . . . . . . . 7–19
Section 8. WEAR LIMITS AND
SPRING DATA
8–1. WEAR LIMIT DATA . . . . . . . . . . . . . . . . . 8–1
8–2. SPRING DATA . . . . . . . . . . . . . . . . . . . . . . 8–1
Section 9. CUSTOMER SERVICE
9–1. OWNER ASSISTANCE . . . . . . . . . . . . . . . 9–1
9–2. SERVICE LITERATURE . . . . . . . . . . . . . . 9–2

x Copyright © 1996 General Motors Corp.
FOLDOUT ILLUSTRATIONS
(Back of Service Manual)
CROSS-SECTION VIEWS
Foldout
1 Model AT 540, 542, 543 Transmission
2 Model AT 545, 1545 Transmission
3 AT Transmission With Retarder
SCHEMATIC VIEW
Foldout
4,A Input Retarder — OFF
4,B Input Retarder — 50% Capacity
4,C Input Retarder — 100% Capacity
5 AT 500 Series Transmissions
6 AT 1500 Series Transmissions
EXPLODED VIEWS
Foldout
7,A Torque Converter Assembly (AT 543)
7,B Torque Converter and Oil Pump Assemblies
8 Forward Clutch and Turbine Shaft
9,A Fourth Clutch
9,B Third Clutch, Second Clutch, and Center Support
10,A Planetary Gear Unit
10,B First Clutch
11 Main Control Valve Body Assembly
12,A Transmission Housing, Governor, and Vacuum Modulator
12,B Oil Pan, Filter, Governor, and Speedometer Drives
13 Retarder Control Components

Copyright © 1996 General Motors Corp. 1–1
1–1. SCOPE OF MANUAL
a. Coverage
(1) This Service Manual describes the opera-
tion, maintenance, and overhaul procedures for the AT
540, AT 542(N)(R)(NFE), AT 543, AT 545(N)(R), AT
1542P, AT 1545P(N) Series automatic transmissions
(Figures 1–1 through 1–4). A description of the major
components of the transmissions, the function and op-
eration of the hydraulic system, wear limits, and in-
spection procedures are included. Torque specifica-
tions are given with each assembly step and on the
exploded view foldouts at the back of this manual.
(2) Because of similarities of all models, in-
structions apply generally to all models. Where proce-
dures vary between models, instructions identify
specific models.
b. Illustrations. Overhaul procedures are illus-
trated mainly by photographs. Line drawings are used
to supplement detailed assembly procedures; cross
sections show torque paths and the relationship of as-
sembled parts. Cross sections, color-coded hydraulic
schematics, and parts exploded views are on foldouts
at the back of this manual. The foldouts may be
opened for reference while studying the text.
c. Maintenance Information. Each task out-
lined in this Service Manual has been successfully ac-
complished by service organizations and individuals.
It is not expected that every service organization or in-
dividual will possess the required special tooling,
training, or experience to perform all the tasks out-
lined. However, any task outlined herein may be per-
formed if the following conditions are met:
(1) The organization or individual has the re-
quired knowledge of the task through:
• Formal instruction in an Allison or
Distributor training facility.
• On-the-job instruction by an Allison or
Distributor representative.
• Experience in performing the task.
(2) The work environment is suitable to pre-
vent contamination or damage to transmission parts or
assemblies.
(3) Required tools and fixtures are available
as outlined in the Service Manual.
(4) Reasonable and prudent maintenance
practices are utilized.
NOTE:
Service organizations and individuals are encour-
aged to contact their local Allison Transmission
Distributor for information and guidance on any of
the tasks outlined herein.
1–2. SUPPLEMENTARY
INFORMATION
Supplementary information will be issued, as required,
to cover any improvements made after publication of
this manual. Check with your dealer or distributor to
ensure you have the latest information.
1–3. ORDERING PARTS
a. Transmission Nameplate. The nameplate
(Figure 1–5) is located on the right-rear side of the
transmission. The nameplate shows the transmission
serial number, part number (assembly number), and
model designation, all three of which must be sup-
plied when ordering replacement parts or requesting
service information.
b. Parts Catalog. Do not order by illustration
item numbers on exploded views in this manual. All
replacement parts should be ordered from your distrib-
utor or dealer. Parts are listed in the current Parts Cata-
logs PC1235EN.
Section 1 – GENERAL INFORMATION

1–2 Copyright © 1996 General Motors Corp.
Figure 1–1. AT 1545 Automatic Transmission — Left-Front View
Figure 1–2. AT 545R Automatic Transmission — Right-Rear View
SHIPPING BRACKET
MODULATOR
RETAINER
SELECTOR
SHAFT
WELDED
TORQUE
CONVERTER
ASSEMBLY
(NOT SEPARABLE)
OIL PAN
GOVERNOR
COVER
BREATHER
H01341
RETARDER CONTROL
VALVE ASSEMBLY
NAMEPLATE
OUTPUT SHAFT
BRAKE MOUNTING
PAD
OIL FILLER
TUBE PORT
DRAIN PLUG
BREATHER
H02874

GENERAL INFORMATION
Figure 1–3. AT 543 Automatic Transmission — Left-Front View
Figure 1–4. AT 542, 543, 1542 Automatic Transmission — Right-Rear View
H02875
GOVERNOR
COVER
TORQUE CONVERTER
RETAINING STRAP
SEPARABLE
TORQUE CONVERTER
OIL PAN
MODULATOR
RETAINER
SELECTOR
SHAFT
H02876
BREATHER
BRAKE
MOUNTING
PAD
OUTPUT
SHAFT
DRAIN PLUG
OIL FILLER
PTO COVER
NAMEPLATE

Figure 1–5. Transmission Nameplate
1–4. GENERAL DESCRIPTION
a. Automatic, Four Speeds. The AT 500 and
1500 Series transmissions have four forward speeds
and one reverse. Shifting within the forward ranges se-
lected by the operator is fully automatic.
b. Torque Converter and Lockup Clutch. An
Allison three-element torque converter (Foldout 1, 2,
or 3) transmits power from the engine to the transmis-
sion gearing. The torque converter serves as both a
fluid coupling and a torque multiplier. AT 1500 Series
transmissions also include a lockup clutch in the
torque converter assembly.
c. Planetary Gearing, Clutches. Ratios for four
forward speeds and reverse are established by plane-
tary gearing. The planetary gearing is controlled by
multiple-disc, hydraulic clutches. All gearing is in
constant mesh.
d. Main Control Valve Body. The main control
valve body consists of a series of spring-loaded spool
valves which are hydraulically actuated by the main
pressure produced from the charging pump.
1–5. OPERATING INSTRUCTIONS
Refer to SA1334 for operating instructions.
1–6. SPECIFICATIONS AND DATA
The specifications and data in Table 1–1 are applicable
to AT 500 and 1500 Series transmissions.
ECAPSOREAELIBOMO
TUA DETINU ACIREMA
FOSREKROWTNEMELP
MI
LARUTLUCIRGA
DNA
UAW
933
DIVISION OF
GENERAL MOTORS
CORPORATION
INDIANAPOLIS
INDIANA
SERIAL NO.
XXXXX
XX XXXXX
XXXXXXX
MODEL
NO.
PART NO.
V01251
Table 1–1. Specifications and Data
INPUT RATINGS — AT 1542 DIESEL
Value
Parameter
General Truck &
Road Sweeper
Transit & Airport
Shuttle Bus
Motorhome School Bus
Inner City &
Shuttle Bus
Unit
Input Speed
Maximum full load governed speed 4000* 4000* 4000* 4000* 4000* rpm
Minimum full load governed speed 2400 2400 2400 2400 2400 rpm
Minimum idle speed in drive 500 500 500 500 500 rpm
Input Power
Maximum net 180 (134) 160 (119) 180 (134) 180 (134) 180 (134) hp (kW)
Input Torque
Maximum net 405 (549) 340 (461) 405 (549) 405 (549) 405 (549) lb ft (N·m)
Turbine Torque
Gross vehicle weight (GVW) 22050 (10002) 16540 (7500) 22050 (10002) 16540 (7500) 18520 (8401) lb (kg)
Gross combination vehicle weight (GCW) 22050 (10002) N/A 27010 (12252) N/A N/A lb (kg)
* 3200 rpm for TC 290

GENERAL INFORMATION
INPUT RATINGS — AT 1542 GASOLINE
Value
Parameter
General Truck &
Road Sweeper
Transit & Airport
Shuttle Bus
Inner City &
Shuttle Bus
Unit
Input Speed
Maximum full load governed speed 4400 4400 4400 4400 4400 rpm
Input Power
Maximum net 200 (149) 160 (119) 200 (149) 200 (149) 200 (149) hp (kW)
Input Torque
Turbine Torque
INPUT RATINGS — AT 1545 DIESEL
Value
Parameter
General Truck &
Road Sweeper
Transit & Airport
Shuttle Bus
Inner City &
Shuttle Bus
Unit
Input Speed
Maximum full load governed speed 4000* 4000* 4000* 4000* 4000* rpm
Input Power
Maximum net 180 (134) 160 (119) 180 (134) 180 (134) 180 (134) hp (kW)
Input Torque
Turbine Torque
* 3200 rpm fors TC 290
INPUT RATINGS — AT 1545 GASOLINE
Value
Parameter
General Truck &
Road Sweeper
Transit & Airport
Shuttle Bus
Inner City &
Shuttle Bus
Unit
Input Speed
Maximum full load governed speed 4400 4400 4400 4400 4400 rpm
Input Power
Maximum net 200 (149) 160 (119) 200 (149) 200 (149) 200 (149) hp (kW)
Input Torque
Turbine Torque
Note: Conversions between inch and metric units are not necessarily equivalent.
Table 1–1. Speciﬁcations and Data (cont’d)

Mounting:
Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAE 3 automotive flywheel
housing with flexplate drive
Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One vertical mounting pad each
side
Drive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flexplate drive, customer fur-
nished
Rotation (viewed from input):
Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clockwise
Output (in forward ranges). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clockwise
Output location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In line with input
Dry weight, approximate (basic configuration):
AT 500 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 lb (131 kg)
AT 1500 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 lb (137 kg)
Parking brake (some models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting provided at rear of
transmission case for OEM-
supplied parking brake.
Output flange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supplied by OEM
Hydraulic System:
Fluid capacity, approx. (excluding external
circuits)
Fill From
Factory
Initial Fill
After Rebuild
Refill After
Servicing
U.S. Qts Liters U.S. Qts Liters U.S. Qts Liters
Shallow oil pan — 4.0 inch (102 mm) 13 12 15 14 9 8.5
Deep oil pan — 5.3 inch (135 mm) 20 19 22 21 16 15
Temperatures*:
Sump (max) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250°F (120°C)
To cooler — converter-out (max) . . . . . . . . . . . . . . . . . . . . . . . . 300°F (150°C)
To cooler — retarder-out (max) . . . . . . . . . . . . . . . . . . . . . . . . . 330°F (165°C)
Normal operation (sump) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160–200°F (71–93°C)
Normal operation (converter-out) . . . . . . . . . . . . . . . . . . . . . . . . 180–220ºF (82–104ºC)
Oil filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refer to Paragraph 3–8
Oil pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Positive displacement
Oil type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refer to Paragraph 3–7
Oil pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Refer to Tables 3–4 through 3–9
Clutches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic-actuated, spring-released,
self-compensating for wear
Power takeoff (converter driven):
Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAE 6-bolt regular duty
Drive gear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 pitch, 55 teeth, 20˚ pressure angle
* Temperature gauge kit available in Parts Catalog.

GENERAL INFORMATION
Table 1–1. Specifications and Data (cont’d)
Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Right side (viewed from rear)
Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Same as engine
Rating (continuous) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 lb ft (270 N·m)
(intermittent). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 lb ft (270 N·m)
Torque Converter:
Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single-stage, 3-element, multiphase
Number of stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Number of elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Stall torque ratio:
AT 540 AT 542 AT 543 AT 545 AT 1542 AT 1545
TC275;1.96:1 x x x x x
TC290;1.72:1 x x x x x
TC350;3.09:1 x
TC370;2.51:1 x
TC375;2.13:1 x
TC380;1.86:1 x
Lockup Clutch No No No No Yes
(3rd and 4th)
Yes
(3rd and 4th)
Typical Shift Sequence (wide open throttle):
AT 500 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auto 1–4 (1C-2C-3C-4C)
AT 1500 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auto 1–4 (1C-2C-3C-3L-4L)
Shift modulation:
(Gasoline). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vacuum
(Diesel). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical/Electronic
Neutral start and reverse signal switches . . . . . . . . . . . . . . . . . . . . . . . . . Supplied by OEM
Speedometer drive:
Type and size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13⁄16-20 UNEF thread for SAE
regular duty — thread type
Drive gears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 teeth
Driven gear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supplied by customer
Gearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constant mesh, spur type, planetary
TRANSMISSION RATIOS (Mechanical**)
Range Clutch(es) Engaged Ratio
Park (AT 542N, 545N, 1545N) First 0
Neutral First 0
First Forward and first 3.45:1
Second Forward and second 2.25:1
Third Forward and third 1.41:1
Fourth Forward and fourth 1.00:1
Reverse Fourth and first 5.02:1
** Overall torque multiplication ratio of transmission (output stalled) is the product of the converter torque multiplication ratio (see torque converter) and
the mechanical (gear) ratio.

NOTES
AT 500, 1500 SERIES AUTOMATIC TRANSMISSIONSAT 500, 1500 SERIES AUTOMATIC TRANSMISSIONS

2–1. SCOPE
This section describes and explains the operation of
the components and systems of AT transmissions.
Where features are common to all models, no refer-
ence will be made to models. Where features are pecu-
liar to a model, the model will be noted.
2–2. MOUNTING
a. To Engine. The front of the transmission
housing is an SAE size 3 flange. This flange is bolted
to the rear of the engine.
b. To Vehicle. Two 5⁄8-11 tapped holes at each
side of the transmission are provided for mounting to
supports in the vehicle.
2–3. INPUT DRIVE
a. For models other than AT 543, six tapped lugs
are on the front of torque converter 1 (Foldout 7,B) for
attachment of a flexible disk drive. The outer bolt cir-
cle of the disk drive is bolted to the lugs. The inner
bolt circle is bolted to the engine crankshaft or crank-
shaft adapter hub.
b. For AT 543 models, six threaded studs are on
the front of torque converter 2 (Foldout 7,A) for the at-
tachment of a flexible disk drive using nuts 1.
2–4. TRANSMISSION HOUSING
Transmission housing assembly 6 (Foldout 12,A) is
cast aluminum. It houses the clutches and gearing, oil
pump, governor, main control valve, and oil pan. A
parking brake mounting surface is provided at the rear.
On the right side is a provision for a power takeoff or
for the retarder control valve, depending upon the type
of model.
2–5. TORQUECONVERTERASSEMBLY
AND LOCKUP CLUTCH
a. Description
(1) AT 500 Series transmissions have torque
converters that include a pump, a turbine, and a stator.
The pump is driven by the engine. The turbine drives
the turbine shaft. The stator is mounted on a freewheel
clutch, the hub of which is splined to a stationary
ground sleeve. The hub of the torque converter pump
drives the transmission input pressure pump.
(2) AT 1500 Series transmissions are
equipped with an automotive-style lockup torque con-
verter. In addition to the pump, stator, and turbine as-
semblies, a lockup clutch and damper assembly is
incorporated. A lockup valve, located in the front sup-
port assembly, controls flow through the torque con-
verter and provides operation in third and fourth
ranges.
(3) AT 540, 542, 545, 1542, or 1545 Series
torque converter 1 (Foldout 7,B) is a closed, welded
unit that cannot be disassembled.
(4) AT 543 torque converter 2 (Foldout 7,A)
is a serviceable assembly.
b. Operation (Foldout 1, 2, or 3)
(1) The torque converter assembly is contin-
uously filled with transmission fluid, which flows
through the converter to cool and lubricate it. When
the converter is driven by the engine, the pump vanes
throw the fluid against the turbine vanes. The impact
of the fluid against the turbine vanes tends to rotate the
turbine.
(2) The turbine, splined to the turbine shaft,
transmits torque to the transmission gearing. At engine
idle speed, the impact of fluid against the turbine vanes
is minimal. At high engine speed the impact of the
fluid is much greater on the turbine, and high torque is
produced.
(3) Fluid thrown into the turbine flows to the
stator vanes. The stator vanes change the direction of
the hydraulic flow (when the stator is locked against ro-
tation), and directs the fluid to the pump in a direction
that assists the rotation of the pump. It is the redirection
of the fluid by the stator that enables the torque con-
verter to multiply input torque.
(4) Greatest torque multiplication occurs
when the turbine is stalled and the pump is rotating at
its highest speed. Torque multiplication decreases as
the turbine rotates and approaches the speed of the
pump.
(5) When turbine speed approaches the
speed of the pump, fluid flowing to the stator begins
striking the backs of the stator vanes. This rotates the
Section 2 – DESCRIPTION AND OPERATION

stator in the same direction as the turbine and pump.
At this point, torque multiplication stops and the con-
verter becomes, in effect, a fluid coupling.
(6) Thus, the torque converter accomplishes
three main functions. It acts as a disconnect clutch be-
cause little torque is transmitted at engine idle speed.
It multiplies torque at low turbine/high pump speed to
give greater starting or driving effort when needed.
And it acts as a fluid coupling to efficiently transmit
engine torque to the transmission gearing during drive,
other than idle or starting.
(7) For AT 1500 Series models, the engage-
ment of the lockup clutch is controlled by the lockup
relay valve which derives its lockup signal from the
3–4 clutch feed pressure. The clutch apply pressure
compresses the lockup clutch plate against the front
cover. Thus, the converter pump and turbine are
locked together and provide a direct drive from the
engine to the transmission gearing. As rotational
speed of the output shaft decreases, the relay valve
automatically releases the lockup clutch. Refer to
Paragraph 2–19f and g for explanation of the hydrau-
lic action.
2–6. OIL PUMP ASSEMBLY
a. Description (Foldout 7,B)
(1) Oil pump assembly 2 includes, in addi-
tion to pump components, front support assembly 17,
main-pressure regulator components 24 through 27,
and, for AT 1500 Series models, lockup valve compo-
nents 30 through 33.
(2) The oil pump consists of driven gear 9
and drive gear 10 which are located in pump body 8.
Pump body 8 is bolted to front support and bearing as-
sembly 16.
(3) The front support assembly includes sta-
tor shaft 19. Front support 21 closes the front of the
transmission and supports the torque converter, turbine
shaft, and forward clutch.
b. Operation (Foldout 7,B)
(1) When the torque converter is rotating, its
rear hub drives pump drive gear 10. Gear 10 is meshed
with the internal teeth of driven gear 9.
(2) The pump gears draw transmission fluid
from the sump. When the flow of fluid fills all the re-
quirements in the transmission, pressure is developed.
Valve 27 in support 16 regulates the flow of fluid from
the pump.
2–7. FORWARD CLUTCH AND
TURBINE SHAFT
a. Description (Foldout 8)
(1) The forward clutch and turbine shaft as-
sembly connects the converter turbine to the other
clutches and gearing in the transmission during every
operational phase of the transmission, including PTO
operation or retarder operation.
(2) The turbine shaft is splined to clutch
housing 9 or 14. The external tangs of clutch plates 27
engage housing 9 or 14. The internal splines of clutch
plates 28 engage hub 26 which transmits torque to the
gearing.
(3) Piston 19 is installed in housing 9 or 14
and is retained by sixteen springs 20, retainer 21, and
snapring 22. Clutch plates 27 and 28 are held in hous-
ing 9 or 14 by fourth clutch driving hub 29 and are re-
tained by snapring 30.
(4) Some models are equipped with power
takeoff drive gear 4 or 32. When used, gear 32 is
splined to housing 9 and retained by snapring 31.
When used, gear 4 is splined to housing 9 and retained
by snaprings 3 and 5.
(5) For models with retarder, refer also to
Paragraph 2–16.
b. Operation (Foldout 8)
(1) Turbine shaft and housing assembly 7 or
11 rotates when the torque converter turbine rotates.
Fourth clutch driving hub 29 also rotates along with
internal-splined fourth clutch plates 3 (Foldout 9,A).
PTO drive gear 4 or 32 (Foldout 8), when included,
also rotates.
(2) When hydraulic pressure is directed to
the piston bore in housing 9 or 14, piston 19 com-
presses clutch plates 27 and 28 against driving hub 29.
This locks clutch hub 26 to housing 9 or 14. Hub 26 is
splined to transmission main shaft 4 (Foldout 10,A).

DESCRIPTION AND OPERATION
(3) When the converter turbine rotates and
the forward clutch is applied, the transmission main
shaft is rotated. This drives the transmission gear set,
and drives the output shaft in any forward range.
(4) The forward clutch is engaged only dur-
ing operation in a forward range, and is always paired
with another clutch (either first, second, third, or
fourth). It is disengaged during neutral and reverse.
(5) In neutral, the forward clutch housing ro-
tates, driving the power takeoff, if so equipped. In re-
verse, the forward clutch housing rotates to drive the
fourth clutch (which is applied in combination with
the first clutch to obtain reverse).
(6) For models with retarder, refer also to
Paragraph 2–16.
2–8. FOURTH CLUTCH
a. Description (Foldout 9,A)
(1) The fourth clutch includes housing as-
sembly 11, piston 8, five external-tanged clutch plates
4, five internal-splined plates 3, and, for models with-
out retarder, backplate 2. For models with retarder, re-
tarder housing 36 (Foldout 8) functions as the fourth
clutch backplate.
(2) Piston 8 (Foldout 9,A) is installed in
housing 13, and retained by sixteen springs 7, retainer
6, and snapring 5. External-tanged plates 4 engage
housing 13. Internal-splined plates 3 are splined to
fourth clutch driving hub 29 (Foldout 8). For models
without retarder, plates 3 and 4 (Foldout 9,A) are re-
tained in housing 13 by clutch backplate 2 and
snapring 1. For models with retarder, plates 3 and 4 are
retained in housing 13 by retarder housing 36 (Foldout
8).
(3) The hub of housing 13 (Foldout 9,A) is
splined to sun gear shaft 3 (Foldout 10,A). The outer
splines on housing 13 (Foldout 9,A) engage internal-
splined plates 3 (Foldout 9,B) of the third clutch.
b. Operation (Foldout 9,A)
(1) When the fourth clutch is released, inter-
nal-splined plates 3 are free of external-tanged plates
4. Plates 3 rotate independent of housing 13, whether
housing 13 is stopped or has a different speed or direc-
tion of rotation.
the piston cavity in housing 13, piston 8 compresses
plates 3 and 4 against backplate 2 or against retarder
housing 36 (Foldout 8). This locks internal-splined
plates 3 (Foldout 9,A) to external-tanged plates 4 and,
in turn, to housing13.
(3) When the fourth clutch is engaged, it is
locked to fourth clutch driving hub 29 (Foldout 8) and
rotates with the turbine shaft.
(4) In fourth range, turbine shaft rotation is
transmitted to sun gear shaft 3 (Foldout 10,A) and to
transmission main shaft 4 by the engaged forward
clutch. The result is direct drive to the output shaft.
(5) In reverse, turbine shaft rotation is trans-
mitted to sun gear shaft 3 while the first clutch (Fold-
out 10,B) is engaged, resulting in reverse rotation of
the transmission output shaft.
2–9. SECOND AND THIRD CLUTCH
AND CENTER SUPPORT
(1) Third clutch includes items 1 through 11.
Second clutch includes items 16 through 25. Center
support assembly 13 serves the two clutches. The front
side of support 15 receives third clutch piston 9. The
rear side of support 15 receives second clutch piston
18. Center support 15 directs fluid to both of these
clutches, as well as to the fourth clutch.
(2) External-tanged clutch plates 4 and 23
engage the transmission housing, and are always sta-
tionary. Internal-splined plates 3 of the third clutch en-
gage housing 13 (Foldout 9,A) of the fourth clutch.
Internal-splined plates 24 (Foldout 9,B) of the second
clutch engage the external splines of front planetary
assembly 8 (Foldout 10,A).
b. Operation of Third Clutch (Foldout 9,B)
(1) When the third clutch is released, inter-
nal-splined plates 3 rotate with fourth clutch housing
13 (Foldout 9,A). The third clutch is released in all
ranges except third.
the third clutch piston cavity (front) of center support
15 (Foldout 9,B), piston 9 compresses plates 3 and 4
against backplate 2. This anchors clutch plates 3 and 4,

and fourth clutch housing 13 (Foldout 9,A) to the
transmission housing, stopping rotation. Since housing
13 is splined to sun gear shaft 3 (Foldout 10,A), the
shaft is held stationary. This provides a reaction for the
gearing and causes the planetaries to produce third
range.
c. Operation of Second Clutch (Foldout 9,B)
(1) When the second clutch is released, in-
ternal-splined plates 24 rotate with front planetary car-
rier assembly 8 (Foldout 10,A). The second clutch is
released during all ranges except second.
the second clutch piston cavity (rear) of center support
15 (Foldout 9,B), piston 18 compresses plates 23 and
24 against backplate 25. This anchors internal-splined
plates 24 and external-tanged plates 23 to the trans-
mission housing.
(3) The internal-splines of plates 24 are
splined to front planetary carrier assembly 8 (Foldout
10,A), holding the carrier stationary. A compound ar-
rangement in the planetaries produces second range.
2–10. FIRST CLUTCH
(1) The first clutch includes piston 9, seven
external-tanged clutch plates 4, seven internal-splined
clutch plates 3, and backplate 2.
(2) Piston 9 is in the rear of the transmission
housing. The external tangs of clutch plates 4 engage
the transmission housing and are always stationary. In-
ternal-splined plates 3 engage rear planetary ring gear
5 (Foldout 10,B) or 53 (Foldout 10,A).
(3) Piston 9 (Foldout 10,B) is retained in the
transmission housing by twenty-two springs 8, retainer
7, and snapring 6. Backplate 2 and clutch plates 3 and
4 are retained in the transmission housing by snapring
1.
(1) When the first clutch is released, inter-
nal-splined plates 3 and rear planetary ring gear 5 or
53 (Foldout 10,A) rotate. The first clutch is released
during operation in all ranges except neutral, first, and
reverse.
the first clutch piston cavity, piston 9 (Foldout 10,B)
compresses clutch plates 3 and 4 against backplate 2.
This locks internal-splined plates 3 to external-tanged
plates 4, which are anchored to the transmission hous-
ing. Plates 3, splined to the rear planetary ring gear,
hold the ring gear stationary.
(3) The stationary ring gear provides a reac-
tion for the planetary gearing to produce either first
range or reverse.
(4) In first range, the driving member is rear
planetary sun gear 31 (Foldout 10,A), which receives
torque through the turbine shaft, the engaged forward
clutch, and the transmission main shaft.
(5) In reverse, the driving member is center
sun gear 19 (Foldout 10,A), which receives torque
through the turbine shaft, the engaged fourth clutch,
and sun gear shaft 3. First range is a simple planetary
action (involving only one planetary). Reverse is a
compound planetary action (involving two planetary
sets).
2–11. PLANETARY GEAR UNIT
a. Description (Foldout 10,A)
(1) The planetary gear unit includes all of
the gears and shafts in the transmission except the tur-
bine shaft and the rear planetary ring gear.
(2) Three planetary gear sets are included in
the assembly. These are called front planetary, center
planetary, and rear planetary.
(3) The front planetary includes sun gear 6,
carrier assembly 8, and ring gear 18. The center plane-
tary includes sun gear 19, carrier assembly 20, and
ring gear 30. The rear planetary includes sun gear 31,
carrier assembly 36, and ring gear 5 (Foldout 10,B).
(4) The three planetary sets are intercon-
nected by sun gear shaft 3 (Foldout 10,A), main shaft
4, and connecting drum 28. This interconnection of the
planetary input, reaction, and output elements, and
connection of clutches to the shafts and planetary ele-
ments, produces four forward ranges and reverse.
b. Operation. Refer to Paragraph 2–19.

2–12. SPEEDOMETER DRIVE/SPEED
SENSOR WHEEL
(1) The speedometer drive consists of drive
gear 2 and provision for mounting the driven gear as-
sembly in the transmission housing. Drive gear 2 is a
worm gear with a left-hand helix. It is concentric with
the transmission output shaft. The drive gear is
clamped between adjacent components for rotational
drive.
(2) Speed sensor wheel 9 is provided for
models that are equipped with an electronic speed-
ometer. The 16-tooth wheel provides a rotating pulse
that can be read by an electronic speed sensor.
(1) When the transmission output shaft ro-
tates, drive gear 2 or speed sensor wheel 9 rotates.
(2) For mechanical speedometers, the driven
gear, supplied by the vehicle manufacturer, rotates
clockwise during forward operation (viewed at the
drive cable connection on the transmission).
(3) For electronic models, the speed sensor,
supplied by the vehicle manufacturer, reads the output
speed by “counting” the pulses produced by the teeth
of the speed sensor wheel.
2–13. GOVERNOR
a. Description (Foldout 12,A). Governor assem-
bly 19 is a centrifugal (ﬂyweight) governor, driven by
drive gear 1 (Foldout 12,B) and mounted on the trans-
mission output shaft. It is retained by cover 22 (Fold-
out 12,A).
b. Operation (Foldout 12,A). When the governor
rotates, centrifugal force causes weights to move out-
ward which moves a valve to admit main pressure to
the governor circuit. Governor pressure is regulated
when the centrifugal force of the weights is balanced
by opposing hydraulic pressure. Governor pressure
varies with transmission output speed, increasing as
output speed increases. Governor pressure, in combi-
nation with modulator pressure, controls the automatic
shifting of the transmission.
2–14. MODULATOR
a. Vacuum Modulator (Foldout 12,A)
(1) Vacuum modulator 26 is calibrated and
sealed at the factory.
(2) The position of the diaphragm in the
modulator varies with vehicle speed, load, and engine
throttle opening. When the diaphragm moves, the
modulator valve is affected, increasing or decreasing
modulation pressure. Modulator and governor pres-
sures control the automatic selection of transmission
ranges.
b. Mechanical Modulator
(1) The mechanical modulator is attached to
the transmission and activated by a cable.
(2) The cable is connected to the fuel control
lever at one end and the modulator valve actuator at
the other. The fuel control lever moves the cable, con-
trolling the modulator valve.
c. Electric Modulator
(1) An electric modulator can be used with
electronic or non-electronic engines — any engine
which can provide an On/Off signal based on throttle/
pedal position.
(2) The 12-volt modulator assembly and the
24-volt modulator assembly utilize an electronic sig-
nal to stroke the transmission modulator pin from the
closed-throttle position to the full-throttle position.
The result is step-modulation.
(3) Step-modulation is a two-phase modula-
tion schedule which utilizes a closed-throttle shift
schedule until the throttle position is greater than 80–85
percent, then, remains at a full-throttle shift schedule
until the throttle position is less than 60–65 percent.
(4) Electric modulators are compatible with
an electronically-controlled engine that can provide an
On/Off signal based on throttle position. Consult the re-
spective engine manufacturer to identify the wire that
provides this signal. Electronic modulation can also be
applicable in mechanically-controlled engines. The
modulating system will still require a 12- or 24-volt (dc)
signal to stroke the transmission modulator valve.

2–15. OIL PAN AND FILTER
(1) Oil pan 26 or 33 is a pressed steel assem-
bly providing openings for draining the transmission
fluid and for mounting a fill tube and dipstick.
(2) Filter assembly 21, 38, or 46 is either a
paper element retained by a steel casing or a brass
screen assembly. The filter tube is not integral to the
filter.
(3) Transmission fluid from the sump is
drawn through the filter by the input oil pump and di-
rected to the hydraulic system. A washer-head screw
attaches the filter to the valve body.
(4) Deep pan units also use spacer 41 or 49
and a longer intake tube 40 or 48 between the filter and
the valve body.
b. Function (Foldout 12,B)
(1) Oil pan 26 or 33 serves as the transmis-
sion fluid sump and covers the main control valve
body assembly and the filter. The oil pan must be re-
moved from the bottom of the transmission to replace
the filter.
(2) The filter assembly screens all transmis-
sion fluid entering the hydraulic system. The fluid
change interval is influenced by whether the transmis-
sion is fitted with a paper or with a brass filter. Refer to
Paragraph 3–8.
(3) In some models, a magnet in the oil pan
helps to accumulate any metal particles in the fluid
supply.
2–16. HYDRAULIC RETARDER
a. Description
(1) AT 542/545R models have a retarder lo-
cated on the input side of the transmission that is de-
signed for auxiliary braking for downhill speed con-
trol. This 160 hp retarder has a two-stage capacity
that, in conjunction with selection of the appropriate
ranges, can be used to tailor desired retardation perfor-
mance to particular duty cycles.
(2) A cross-section of the AT 542/545R is
shown on Foldout 3. The main retarder components
internal to the transmission are front stator 1 (Foldout
8), the rotor which is a part of forward clutch housing
14, and rear stator 35.
(3) The AT retarder has a dual torus design.
The retarder rotor provides high flow and torque gen-
eration. Front stator 1 and rear stator 35 are both sta-
tionary.
(4) The rotating element (rotor) of the re-
tarder is cast on the OD of forward clutch housing 13.
The rotor blades occupy approximately the same area
that the optional PTO gear occupies on a PTO-
equipped AT transmission. The valve body for the re-
tarder mounts to the transmission PTO pad. Transmis-
sion fluid is transferred to and from the retarder
through tubes that connect the externally-mounted re-
tarder controls to retarder housing 37.
b. Operation
(1) The hydraulic system introduces trans-
mission fluid through the tips of the rear stator blades
in rear housing assembly 35 (Foldout 8), which is an
extremely low pressure area. The fluid exits the torus
through a slot at the OD of the blades.
(2) The retarder fluid is transferred from the
retarder housing to the controls through two tubes. The
controls turn on the retarder, as well as perform capac-
ity regulation and cooler oil routing.
(3) The retarder is electronically activated by
solenoids (Foldout 4,A, B, and C). Main-pressure
from Solenoid H activates the autoflow valve. This
valve routes transmission cooler flow and fills the re-
tarder cavity through a regulator valve and priority
valve system.
(4) The routing of the fluid to the cooling
system is accomplished with the autoflow valve. When
closed, the transmission fluid is routed through both
primary and secondary coolers and the filter system.
When in retarder mode, the auto-flow valve opens and
directs converter-out transmission fluid through the
secondary cooler and filter system. Retarder fluid
flows through the primary cooler only.

(5) The retarder priority valve allows the
regulator valve to feed the retarder if transmission
fluid pressure is at an acceptable level. This is done to
prevent the apply of the retarder from occurring if
main pressure is at a low enough level that the trans-
mission would be unable to acceptably transmit the re-
tarder torque. The priority valve also acts as a retarder
capacity interrupt during transmission range shifts,
preventing transmission clutch overloads. The priority
valve strokes as a result of the usual transmission main
pressure drop that occurs when filling a clutch during a
range shift. This pressure drop results in the retarder
priority valve closing, and retarder capacity being re-
duced during the shift. This interruption in retarder is
so brief that no negative impact on performance is
noted. The brief capacity reduction also improves the
quality of the downshift while the retarder is activated.
(6) The retarder control system has the abil-
ity to incorporate two levels of braking, using a special
regulator valve. The regulator valve balances retarder
charging pressure against a resisting force that varies
at two levels dependent upon the capacity level cho-
sen.
(7) For the lower capacity (50 percent), the
valve spring force acts alone to balance the charging
pressure to produce torque. The first stage solenoid
(Solenoid H) is the only solenoid energized for this ca-
pacity level.
(8) The control system for the higher capac-
ity level (100 percent) uses the second stage solenoid
(Solenoid F) in addition to the first stage solenoid. The
hydraulic output from Solenoid H supplements the
spring force via a small plug valve. This raises the
charging pressure required to establish a force balance
on the regulator valve, resulting in higher braking out-
put when both solenoids are energized.
(9) Retarder torque is generated by the rotat-
ing rotor blades which pump transmission fluid into a
set of stationary stator blades. The stationary blades, in
turn, redirect the fluid back to the rotating blades. The
result is a very high velocity hydraulic flow around the
torus and the absorption of a large amount of kinetic
energy. Cooler flow results from the large pressure
drop that the high velocity fluids create between the
inlet and outlet locations.
2–17. MAIN CONTROL VALVE
ASSEMBLY
Main control valve body assembly 1 (Foldout 11) in-
cludes valves, springs, and other components which
respond to the manual selection of ranges and control
the automatic shifting of the transmission. The valve
body assembly is bolted to the bottom of the transmis-
sion housing. The transmission housing is channeled
to direct the flow of transmission fluid between the
valve body and clutches and other components.
2–18. HYDRAULIC SYSTEM
NOTE:
References to up, down, left, or right refer to posi-
tions or movements of components on Foldout 5 or 6.
a. System Functions. The hydraulic system gen-
erates, directs, and controls the pressure and flow of
hydraulic fluid within the transmission. Hydraulic
fluid (transmission oil) is the power transmitting me-
dium in the torque converter. Its velocity drives the
torque converter turbine. Its flow cools and lubricates
the transmission. Its pressure operates the control
valves and applies the clutches.
b. System Schematic (Foldout 5 or 6). Color-
coded foldouts of the hydraulic systems are presented
at the back of this manual. The illustrations represent
the system as it functions in neutral with the engine
idling.
c. Filter, Pump Circuit. Transmission fluid is
drawn from the sump through a filter screen by the in-
put-driven charging pump. Fluid discharged by the
pump flows to the main-pressure regulator valve. A
bypass circuit returns fluid to the pump intake when
main pressure reaches its scheduled value.
d. Main-Pressure Circuit (Red)
(1) Transmission fluid from the pump flows
into the bore surrounding the main-pressure regulator
valve, into an internal passage of the valve, and to the
upper end of the valve. Pressure at the upper end of the
valve moves the valve downward until fluid flows to
the torque converter and, if pump flow is of sufficient
volume, to the bypass circuit. Spring force below the

valve, balanced with hydraulic pressure above the
valve, creates a regulated main pressure.
(2) The main-pressure circuit to the remain-
der of the hydraulic system is connected to the main-
pressure regulator valve bore at the same point as the
pump outlet. Before S/N 34501 (AT 540, 543 models),
main pressure is directed to seven points in the system.
These are the 3–4 shift signal valve, 2–3 shift signal
valve, 1–2 shift signal valve, selector valve, 1–2 relay
valve, modulator valve, and governor valve. After S/
N 34500 (AT 540, 543 models) and for all other AT
models, the trimmer regulator valve and the priority
valve are also in the main-pressure circuit.
(3) Although main pressure is controlled pri-
marily by the force of the spring below the regulator
valve, modulator pressure (earlier models), and for-
ward regulator pressure reduce main pressure.
(4) On AT 542, 543, 545, 1542, and 1545
models, main pressure remains constant because there
is no modulated pressure at the main-pressure regula-
tor valve.
e. Converter-In (Yellow), Converter-Out
(Orange), Lubrication (Green) Circuits
(1) Converter-in fluid flows through the
torque converter continuously to keep it filled and to
carry off the heat generated in the converter.
(2) Converter-out fluid, leaving the torque
converter, flows to an external cooler (supplied by the
vehicle or power unit manufacturer). A flow of air or
water over or through the cooler removes the heat
from the transmission fluid.
(3) Cooler-out fluid returns to components
requiring continuous flow lubrication. Lubrication
fluid then returns to the sump.
f. Selector Valve, Neutral, Forward Regulator
Circuit (Orange and Yellow)
(1) The selector valve is manually shifted to
select the operating range desired. The selector valve
establishes the hydraulic circuit for operation in the
range selected. Shifting within any range is automatic,
depending upon speed and throttle position.
(2) Neutral, forward regulator pressure is di-
rected from the selector valve to the main-pressure
regulator valve when the selector valve is at any posi-
tion except reverse. In neutral and in all forward
ranges, this pressure pushes downward on the main-
pressure regulator valve and reduces main pressure. In
reverse, regulator pressure is absent, permitting a
higher main pressure.
g. Governor Valve, Governor Circuit
(Green and White)
(1) Governor feed is main pressure directed
to the governor valve. The governor controls the po-
sition of the governor valve, which determines the
pressure in the governor circuit. When the trans-
mission output is not rotating, governor pressure is
approximately 2 psi (14 kPa). When the transmis-
sion output rotates, governor pressure varies with
the speed of rotation. The greater the speed of rota-
tion, the greater the governor pressure.
(2) Governor pressure is directed to the 1–2,
2–3, and 3–4 shift valves.
h. Modulator Pressure Circuit (Red and Green)
(1) Modulator pressure is a regulated, re-
duced pressure derived from main pressure at the mod-
ulator valve. Pressure is applied by either a vacuum
modulator or a mechanical actuator. At high vacuum
(closed throttle), all pressure is removed from the actu-
ator pin allowing the valve to move rightward. Low
vacuum (open throttle) increases the pressure on the
actuator pin, due to the spring force in the vacuum
modulator, moving the valve leftward.
(2) When the modulator pressure valve
moves to the left, modulator pressure is reduced; when
it moves to the right, modulator pressure is increased.
Since engine vacuum varies with load, throttle open-
ing, and engine speed, the position of the modulator
pressure valve, and modulator pressure vary also. On
the AT 542, 543, 545, 1542, and 1545 models, this
varying pressure is directed to the three shift signal
valves and to the trimmer regulator valve. On the AT
540, modulated pressure is directed also to the main-
pressure regulator valve.
(3) At the 1–2, 2–3, and 3–4 shift signal
valves, modulator and governor pressures act to up-
shift the valves in proper sequence. At a given gover-
nor pressure, the introduction of modulator pressure
upshifts a signal valve. A decrease or removal of mod-

ulator pressure causes a downshift if governor pressure
alone will not hold the valve upward against spring
force.
(4) For the earlier models main-pressure reg-
ulator valve, modulator pressure exerts a downward
force on the valve. An increase in modulator pressure
causes a decrease in main pressure; a decrease in mod-
ulator pressure causes an increase in main pressure.
(5) Before S/N 34501, modulator pressure is
blocked by the separator plate at the trimmer regulator
valve. The trimmer regulator valve is either isolated
and not functional or is not present.
(6) After S/N 34500, modulator pressure is
directed to the trimmer regulator valve, exerting an
upward force against its spring. This causes a reduc-
tion in trimmer regulator pressure at the trimmer
valves.
i. Clutch Circuits
(1) Each of the five clutches has its own cir-
cuit. Each clutch, except forward, is connected to a re-
lay valve and a trimmer valve. The forward clutch is
connected directly to the selector valve. It does not re-
quire connection to a trimmer valve because its appli-
cation (except in a neutral-to-first range shift) precedes
the application of an additional clutch, which is
trimmed.
(2) The first clutch circuit (red and white)
connects the clutch to the 1–2 relay valve and to the
first clutch trimmer valve. In neutral, the 1–2 relay
valve is held upward by spring force, and main pres-
sure is directed to the first clutch circuit. The 1–2 relay
valve does not move downward unless the 1–2 signal
line is charged. This will not occur in neutral because
there is no governor pressure to shift the 1–2 signal
valve.
j. Hold Regulator Valve
(1) The various hold ranges limit the high-
est range attainable by introducing a pressure which
prevents governor pressure from upshifting the signal
valves. This pressure is a regulated, reduced pressure
derived from main pressure at the hold regulator
valve.
(2) Hold regulator pressure at each shift sig-
nal valve will push the modulator valve upward, and
hold the shift valve down against governor pressure.
Thus, when hold regulator pressure is present, an up-
shift can occur at that shift signal valve only with ex-
cessive overspeed.
k. Automatic Upshifts
(1) When the transmission is operating in
first range (or second range, earlier model transmis-
sions with second range start), with the selector valve
at D (Drive), a combination of governor pressure and
modulator pressure, or governor pressure alone, will
upshift the transmission to the next range. At closed or
part throttle, modulator pressure assists governor pres-
sure. At full throttle, there is no modulator pressure.
Thus, upshifts occur sooner when the throttle is closed
and are delayed when the throttle is open.
(2) When governor pressure is sufficient, the
first upshift will occur. A further increase in governor
pressure (output speed) will cause subsequent up-
shifts.
(3) In any automatic upshift, the shift signal
valve acts first. This directs a shift signal pressure to
the relay valve. The relay valve moves downward, ex-
hausting the applied clutch and applying a clutch for
the next higher range.
l. Automatic Downshifts
(1) Automatic downshifts, like upshifts, are
controlled by governor and modulator pressures.
Downshifts occur in sequence as governor pressure
and/or modulator pressures decrease. Low modulator
pressure (open throttle) will cause a sooner downshift;
high modulator pressure (closed throttle) will cause a
delayed downshift.
(2) In any automatic downshift, the shift sig-
nal valve acts first. This exhausts the shift signal hold-
ing the relay valve downward. The relay valve then
moves upward, exhausting the applied clutch and ap-
plying the clutch for the next lower range.
m. Downshift Inhibiting
(1) Inherent in the system is a means for pre-
venting downshifts at a too rapid rate. For example, if
the vehicle is traveling at a high speed in fourth range

and the selector valve is shifted to 1 (Drive 1), the
transmission will not immediately shift to first range.
Instead, it will shift 4–3–2–1 as speed decreases (it
will remain in fourth range if speed is not decreased
sufficiently to allow an automatic downshift).
(2) The progressive downshift occurs be-
cause the regulated hold pressure is calibrated to move
the signal valves downward against governor pressure
only when the governor pressure decreases to a value
corresponding to a safe downshift speed. Thus, if
speed is too great, governor pressure is sufficient to
hold the shift signal valve upward. As governor pres-
sure decreases, the shift signal valves move downward
in sequence.
n. Trimmer Valves
(1) There are four trimmer valves in the hy-
draulic system. These are: first clutch trimmer, second
clutch trimmer, third clutch trimmer, and fourth clutch
trimmer. The purpose of a trimmer is to avoid harsh
shifts.
(2) All four trimmers function in the same
manner. Each trimmer includes an orificed trimmer
valve, a plug, a trimmer spring or springs, and a stop.
The trimmer spring or springs hold the plug and trim-
mer valve to the top of the valve bore.
(3) When any clutch (except forward) is ap-
plied, apply pressure is sent also to the upper end of
the trimmer valve. Initially, the valve and plug are
moved downward against the plug spring until the
circuit exhausts. This escape of fluid, as long as it
continues, reduces clutch apply pressure. The trans-
mission fluid flows through an orifice in the trimmer
valve to the cavity between the trimmer valve and
plug. Pressure in this cavity moves the plug downward
to the stop. Main pressures above and below the trim-
mer valve equalize. The pressure below the trimmer
valve, because it is acting upon a greater diameter,
pushes the trimmer valve to the top of the valve bore.
This throttles, then stops, the exhaust of the fluid.
When escape of fluid stops, clutch-apply pressure is at
maximum value. The plug remains downward, against
the stop, until the clutch is released.
(4) When the transmission is shifted into re-
verse, clutch-apply pressure is directed to the top and
bottom of the fourth clutch trimmer valve. This equal-
izes the pressure at both ends of the valve, thereby
holding the trimmer valve and valve plug at the top of
the bore. No trimming action occurs in reverse.
(5) Whenever a clutch is released, the
spring(s) push the trimmer components to the top of
the bore. In this position, the trimmer is reset, ready to
repeat its trimming action when the clutch is again en-
gaged.
o. Priority Valve
(1) The priority valve ensures that the control
system upstream from the valve (governor, modulator,
forward clutch) will retain sufficient pressure during
shifts to perform its automatic functions.
(2) On models before S/N 34501, main
pressure is routed directly to the 1–2 relay valve, thus
eliminating the priority valve function until the
selector valve is moved. On models after S/N 34500,
main pressure is routed directly to the priority valve,
thereby including the 1–2 signal valve in those
receiving pressure priority.
p. Trimmer Regulator Valve
(1) The trimmer regulator valve reduces
main pressure to a regulated pressure circuit (red and
yellow). The regulated pressure is raised or lowered by
changes in modulator pressure.
(2) Trimmer regulator pressure is directed to
the spring end of the first and second clutch trimmer
valves to increase the clutch-apply pressure of the
trimmer valves. A higher modulator pressure (closed
throttle) reduces trimmer regulator pressure, resulting
in lower clutch-apply pressure. Conversely, a lower
modulator pressure (open throttle) results in higher
regulator pressure and higher clutch-apply pressure.

(3) Downward movement of the first or
second clutch trimmer displaces transmission fluid
into the trimmer regulator circuit. The trim boost
accumulator valve absorbs the displaced transmission
fluid, allowing for smooth clutch application.
2–19. TORQUE PATHS THROUGH
TRANSMISSION
a. Converter Operation. Power is transmitted
hydraulically through the torque converter. The engine
drives the converter pump. The pump throws
transmission fluid against the vanes of the turbine,
imparting torque to the converter turbine shaft. From
the turbine, the fluid flows between the vanes of the
stator, and re-enters the converter pump where the
cycle begins again. The torque path through the torque
converter is identical in all drive situations and in
neutral. When the engine is idling, impact of the fluid
upon the turbine vanes is negligible. When the engine
is accelerated, the impact is increased and the torque
produced in the converter turbine shaft can exceed the
engine torque (by an amount equal to the torque ratio
of the converter).
b. Neutral Operation (Figure 2–1)
(1) Torque produced in the torque converter
is not transmitted beyond the turbine shaft and
forward clutch housing assembly. Only first clutch is
applied. Because two clutches must be applied to
produce output shaft rotation, no output rotation
occurs.
(2) For AT 1500 Series models, the lockup
clutch does not apply during neutral operation.
Figure 2–1. Neutral Power Flow
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V02877
TURBINE SHAFT
SUN GEAR SHAFT
PTO GEAR
FORWARD CLUTCH
THIRD CLUTCH
SECOND CLUTCH
FIRST CLUTCH
FOURTH CLUTCH✽TORQUE
CONVERTER
ASSEMBLY
MAIN SHAFT TORQUE PATH
✽AT 1500 Series models include a lockup clutch, not active in neutral
CLUTCH APPLIED
OUTPUT
SHAFT

c. First-Range Operation (Figure 2–2)
(1) The forward and first clutches are ap-
plied. The first clutch application anchors the rear
planetary ring gear against rotation. The forward
clutch application locks the turbine shaft and transmis-
sion main shaft together to rotate as a unit. The rear
sun gear is splined to the main shaft and rotates with it
and, in turn, rotates the rear planetary pinions. The
pinions are part of the carrier assembly which is
splined to the transmission output shaft. With the rear
ring gear held stationary by the applied first clutch and
the rear sun gear rotating the pinions, the rear plane-
tary carrier rotates within the ring gear and drives the
output shaft at a speed reduction of 3.45:1.
(2) For AT 1500 Series models, the lockup
clutch does not apply during first range operation.
Figure 2–2. First Range Power Flow
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V02878
TURBINE SHAFT
SUN GEAR SHAFT
PTO GEAR
FORWARD CLUTCH
THIRD CLUTCH
SECOND CLUTCH
FIRST CLUTCH
FOURTH CLUTCH✽TORQUE
CONVERTER
ASSEMBLY
MAIN SHAFT TORQUE PATH
✽AT 1500 Series models include a lockup clutch, not active in first range
CLUTCH APPLIED
OUTPUT
SHAFT

Allison transmission at 545 Repair Workshop Service Manual

Allison transmission at 545 Repair Workshop Service Manual

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Allison transmission at 545 Repair Workshop Service Manual