Chapter 8
Gears and Shafts
Upon completion and review of this chapter, the student should be able to:
Classroom Manual Objectives

Identify the components in a basic
planetary gearset and describe their
operation.

Describe how different gear ratios are
obtained from a single planetary gearset.

Describe the construction and operation of
typical Simpson gear-based transmissions.

Describe the construction and operation of
Ravigneaux gear-based transmissions.

Describe the construction and operation of
transmissions that use planetary gearsets
in tandem.

Describe the purpose of a differential.

Identify the major components of a
differential and explain their purpose.

Describe the various gears in a differential
assembly and state their purpose.

Explain the operation of a FWD differential
and its drive axles.

Describe the different designs of fourwheel-drive systems and their
applications.

Discuss the purpose of the various shafts
found in today’s automatic transmissions
and transaxles.
Shop Manual Objectives

Inspect, measure, and replace thrust
washers and bearings.

Inspect and replace bushings.

Inspect and measure a planetary gear
assembly, and replace parts as necessary.

Inspect and replace shafts.

Remove and install the various types of
shaft seals.

Inspect, repair, or replace transaxle drive
chains, sprockets, gears, bearings, and
bushings.

Inspect and replace parking pawl, shaft,
spring, and retainer.

Inspect, measure, repair, adjust, or
replace transaxle final drive components.
Overview
This chapter in both manuals covers planetary gears and shafts, their design variations,
applications, and service.
Reading Assignments
Classroom Manual, pages 249-276
Shop Manual, pages 325-353
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Terms to Know
Annulus gear
Internal gear
Selective thrust washers
Etching
Pinion gear
Thrust load
Interaxle differential
Reaction member
Lecture Outline and Notes
I. Objectives
Review the chapter’s objectives.
II. Simple Planetary Gearsets
A. Review of Gear Theory
1. Discuss the use of levers and gears.
2. Introduce automatic transmission gears.
B. Planetary Gears
1. Discuss the possible gear ratios available with planetary gearsets.
2. Discuss gear reduction with planetary gearsets.
3. Describe direct drive in a planetary gear system.
4. Describe overdrive using planetary gear systems.
5. Describe reverse with a planetary gearset.
6. Discuss neutral with planetary gearsets.
7. Discuss compound planetary gearsets.
III. Planetary Gear Assemblies
A. Simpson Gearset
1. Describe the members of this type of gear train.
2. Explain how ratios and rotations are obtained.
3. Discuss basics of gearset power flow.
B. Ravigneaux Gearset
1. Describe the members of this type of gear train.
2. Explain how ratios and rotations are obtained.
3. Discuss basics of gearset power flow.
C. Planetary Gearsets in Tandem
1. Describe the members of this type of gear train.
2. Explain how ratios and rotations are obtained.
3. Discuss basics of gearset power flow.
D. Non-Planetary Based Transmissions
Describe the operation of Honda’s non-planetary transmission.
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Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E
E. Planetary Gear Service
1. Discuss the need for careful inspection.
2. Explain measuring procedures.
3. Discuss the need for setting clearances to specifications.
IV. Final Drives and Differentials
A. Differential Units
1. Review differential operation and purpose.
2. Describe the maintenance of final drive assemblies used in transaxles.
B. Final Drive Components
Explain the operation of final drives.
V. 4WD Design Variations
A. Discuss the control variations of 4WD gears.
B. Describe how a transfer case works.
C. Describe how a viscous clutch works.
VI. Shafts
A. Types and Location of Shafts
Discuss the location, and the reason for this location, of the various shafts
found in today’s transmissions and transaxles.
B. Shaft Service
1. Describe inspecting the shafts for scores and wear.
2. Discuss how to determine if the shafts can be reused.
VII. Thrust Washers, Bushings, and Bearings
A. Location and Purpose of Bearings, Bushings, and Thrust Washers
1. Discuss the different types of bearings and thrust washers.
2. Discuss transmission bushings and where they are typically used.
B. Thrust Washer, Bushing, and Bearing Service
1. Discuss the maintenance of thrust washers, bushings, and bearings.
2. Explain how to select the correct thrust washer or bearing.
C. Snap Rings
1. Discuss the various types of snap rings used in today’s transmissions.
2. Explain what a selective snap ring is.
VIII. Parking Pawl
A. Theory
Explain the purpose of a parking pawl and how it is activated.
B. Service
Describe parking pawl inspection and service.
Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E
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IX. Drive Chains
A. Theory
Explain the purpose of drive chains and when they are used.
B. Service
Describe how to inspect and test a drive chain.
X. Transfer Gears
A. Theory
Explain the purpose of transfer gears and why they are used.
B. Service
Discuss the typical procedures for inspecting and checking the transfer gears
in a transaxle.
XI. Summary
Review the material covered, emphasizing the main points and key words.
Chapter 8 Answers to Review Questions
CLASSROOM MANUAL, PAGES 277-279
Short Answer Essays
1. If any two of the planetary gearset members receive power in the same direction and at the same
speed, the third member is forced to move with the other two and direct drive results.
2. The input shaft connects the output of the torque converter to the driving members inside the
transmission. The output shaft connects the driven member of the gearsets to the final drive
gearset.
3. There are two common designs of compound gearsets: the Simpson gearset, in which two
planetary gearsets share a common sun gear, and the Ravigneaux gearset, which has two sun
gears, two sets of planet gears, and a common ring gear.
4. If the planet carrier is held and the sun gear is rotated in a clockwise rotation, the ring gear will
rotate in a counterclockwise direction. The planet gears cannot travel around the teeth of an
enmeshed gear; rather, the carrier is held in place and the planet gears spin on their shafts. The
sun gear spins the planet gears, which drive the ring gear in the opposite direction but at a slower
speed. Therefore the gearset is providing reverse gear with reduction.
5. Gear reduction is accomplished in a planetary gearset by holding the sun gear. If power is applied
to the ring gear, the planet gears will spin on their shafts in the planet carrier. Because the sun
gear is being held, the spinning planet gears will walk around the sun gear and carry the planet
carrier with them; this causes a gear reduction. Gear reduction can also occur if the ring gear is
held and the sun gear is the input gear. The planet carrier rotates around the sun gear, but turns
more slowly than it did when the ring gear drove the planet carrier.
6. As the vehicle goes around a corner, the inside wheel travels a shorter distance than the outside
wheel. The inside wheel must therefore rotate more slowly than the outside wheel. An equal
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Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E
percentage of speed is removed from one axle and given to the other; however, an equal amount
of torque is applied to each wheel.
7. A transfer case divides transmission output to the two different drive axles to provide for fourwheel drive.
8. These transaxles have a main shaft and countershaft on which the gears ride. The two shafts run
parallel to each other, and some later models have a third parallel shaft. To provide the forward
gears and one reverse gear, different pairs of gears are locked to the shafts by hydraulically
controlled clutches. Reverse gear is obtained, on some models, through the use of a shift fork that
slides the reverse gear into position. The power flow through these transaxles is also similar to
that of a manual transaxle.
9. When there is input into a planetary gearset but a member is not held, neutral results.
10. When two gearsets are in tandem, the front ring gear is normally connected to the rear carrier and
the rear ring gear is connected to the front carrier.
Fill-in-the-Blanks
1. External, internal
2. Sun, ring
3. Direction, speed, direct
4. Sun gear, planetary carrier, ring gear
5. Annulus, internal
6. Increased, decreased
7. Planet carrier
8. Interaxle
9. Planet, ring, sun
10. Sun, planet, ring
Multiple Choice
1. B
2. B
3. D
4. D
5. C
6. A
7. C
8. C
9. C
10. C
SHOP MANUAL, PAGES 353-354
Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E
57
ASE-Style Review Questions
1. A
2. C
3. C
4. B
5. C
6. B
7. C
8. C
9. B
10. D
ASE Challenge Questions
1. B
2. D
3. C
4. C
5. A
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Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E