Manual Drivetrains and Axles Fourth Edition

OBJECTIVES:
After studying this presentation, the reader
should be able to:
Prepare for the ASE Automatic
Transmission/Transaxle (A2) certification test
content area “A” (General Transmission/Transaxle
Diagnosis)
Explain how a torque converter can transmit and
multiply engine torque
Describe how a planetary gear set can be used for
gear reduction and reverse
Continued

OBJECTIVES:
After studying this presentation, the reader
should be able to:
Explain how automatic transmission fluid is
circulated through the system and how it is cooled

KEY TERMS:
compound planetary gear set • coupling phase
flexplate
impeller • input member
lapelleties gear set • lube oil
output member
pump
ravigneaux gear set • reaction member
Continued

KEY TERMS:
simpson gear set • stall speed • stator
torque converter clutch (TCC) • torque multiplication
phase • turbine

Automatic transmissions were first used on a large scale
in the late 1940s, and now about 85% of the vehicles in
North America are so equipped.
Unlike manual transmissions, most automatic
transmissions do not actually “shift gears” but apply
clutches (or bands) to hold various sections of two or
more planetary gear sets.
The torque converter is attached between the engine and
the transmission/ transaxle and transmits and
multiplies engine torque.

TORQUE CONVERTERS
The impeller, also known as the pump, is the driving member and
rotates with the engine. The impeller vanes pick up fluid in the converter
housing and direct it toward the turbine.
Fluid flow drives the turbine, and when the flow between the impeller
and turbine is adequate, the turbine rotates and turns the transmission
input shaft. A torque converter contains the stator, or reactor, a reaction
member mounted on a one-way clutch.
The vanes used in each of the three elements of a torque converter are
curved to increase the diversion angle of the fluid. This also increases
the force exerted by the fluid and improves the hydraulic advantage. See
Figure 100–1.
Continued

Figure 100–1 A cross-sectional view of a Chrysler Power Flight 2-speed automatic transmission used in the 1950s. Most of
the heat generated in an automatic transmission is created in the torque converter. This air-cooled unit has a vent to allow
hot air to escape.
Continued

The outlet side of the impeller vanes accelerates the fluid as it
leaves the impeller to increase torque transfer to the turbine.
See Figure 100–2.
The inlet side of the turbine vanes absorb shock and limit power
loss that occurs when flow between the impeller and turbine
suddenly changes. The curve of the stator vanes is opposite to the
curve of the impeller and turbine vanes.
See Figure 100–3.
Since the stator is located between the impeller and turbine, it adds
to the original impeller flow and multiplies the force delivered to
the turbine. See Figure 100–4.
Continued

Figure 100–2 Fluid flow within a torque converter. The stator redirects the fluid that is thrown out by the turbine, thereby
improving efficiency.
Continued

Figure 100–3 Fluid pumped into the
turbine by the impeller not only creates
rotary fluid flow but also vortex flow that
increases the efficiency of the torque
converter.
Continued

Figure 100–4 The vane curvature of each element in a
torque converter helps maintain efficient fluid flow
Torque converters are single-piece,
welded assemblies that cannot be
disassembled or repaired easily.
Although they can be rebuilt using
specialized equipment, most shops
simply replace welded converters as
a unit if they fail.
Continued

Torque Converter Attachments The torque converter normally
attaches to the engine through a flexplate that mounts on the
crankshaft flange of the engine.
The flexplate replaces the heavy flywheel used with a manual
transmission. An important function of a flywheel is to smooth out
engine pulsations and dampen vibrations.
An automatic transmission does not require a conventional
flywheel because the fluid in the torque converter provides
enough mass to dampen engine vibrations.
See Figure 100–5.
Continued

Figure 100–5
The torque converter bolts to the flexplate,
which is attached to the crankshaft and
rotates at engine speed. The hub of the
converter drives the oil pump directly on
most rear wheel-drive transmissions.
An external ring gear
generally attaches to the
outer rim of the flexplate.
This ring gear engages the
starter motor pinion gear
to turn the engine during
starting.

NOTE: On some older applications, such as the Ford C4 and Chrysler
Torqueflite, the ring gear may be welded to the outside of the torque
converter cover.
To ensure the pump will deliver fluid to the transmission whenever the engine
turns, an integral hub is located on the converter housing and directly engages
the pump.
Oil pump drive shafts generally pass through the converter inside
a hollow input or transfer shaft and internally connect to the converter housing
by splines.
Most rear-wheel-drive transmissions use an inline method to drive the converter
and provide a direct mechanical connection between the turbine and the
transmission input shaft.
See Figure 100–6.

Figure 100–6 The inner oil pump gear is keyed to the hub of the torque converter, which drives the pump. Notice that the
hub does not engage the full depth of the gear. This is the major reason why the torque converter must be fully installed.
Failure to fully engage the oil pump gear can cause serious damage to both the pump and the torque converter.
Continued

In a typical design, splines on the turbine connect it to the
transmission input shaft and the stator hub mounts on a one-way
overrunning clutch.
The one-way clutch mounts on splines to a stationary extension
of the oil pump called the stator support, or reaction shaft. The
converter drive hub at the rear of the torque converter housing
passes over the stator support and through the front oil seal to
drive the oil pump.
See Figure 100–7.
Continued

Figure 100–7
The transmission input shaft connects
directly to the turbine through splines
in most rear-wheel-drive
transmissions.
Continued

Many transaxles, and a few rear-wheel-drive transmissions, use an
offset drive arrangement to conserve space.
An offset drive design generally uses a drive chain to provide the
mechanical connection between the turbine and the input shaft.
The oil pump may be driven directly by the converter housing or
by a separate drive shaft.
See Figure 100–8.
Continued

Figure 100–8 On a transaxle, the turbine drives the input shaft through a drive chain assembly.
Continued

Torque Converter Operation Fluid sent to the torque converter
from the transmission oil pump is picked up by the rotating vanes
of the impeller and transferred to the turbine vanes through rotary
and vortex flow paths.
Torque Multiplication Phase Fluid leaving the turbine vanes
strikes the concave, or front side, of the stator vanes during the
torque multiplication phase.
The force of the fluid from the stator adds to the force of the fluid
flowing from the impeller to increase the overall torque being
transferred from the impeller to the turbine.
Torque multiplication occurs whenever the vortex flow makes a
full cycle from impeller to turbine, then through the stator and back
to the impeller. See Figure 100–9.
Continued

Figure 100–9 Torque multiplication occurs when fluid leaving
the turbine strikes the front of the stator vanes and is
redirected back to the impeller.
A torque converter multiplies
torque in relation to speed ratio.
At low ratios, the impeller is
turning much faster than the
turbine, so vortex flow is high
and torque multiplication occurs.
As the speed ratio approaches
90%, torque multiplication
becomes minimal and a torque
converter functions like a fluid
coupling.
Continued

The stator redirects fluid flow because it remains stationary during
the torque multiplication phase. The stator hub mounts on a oneway
clutch, freewheeling in a clockwise direction, but locking
when driven in a counterclockwise direction.
Figure 100–10 A stator contains a one-way roller
clutch, which locks it from rotating in one direction
and allows it to rotate freely in the opposite direction.
When fluid from the turbine strikes the concave face of the stator
vanes, it tries to drive the stator counterclockwise. By locking the
stator it can redirect the fluid back to the impeller. Continued

Coupling Phase When the speed ratio is 90% or more, fluid flow in the
toque converter is mostly rotary flow and the angle of flow from turbine
to stator increases.
Fluid eventually strikes the convex side, or backside, of the stator vanes
rather than the concave. As the force of fluid striking the backside
becomes great enough to drive the stator clockwise, the one-way clutch
overruns.
With the clutch overrunning the turbine, impeller, and stator, all rotate in
the same direction and at approximately the same speed. This is called
the coupling phase.
The stator unlocks and freewheels once the angle of fluid flow changes
enough to strike the opposite side of the stator vanes and rotate the stator
clockwise.
Continued

Torque multiplication drops as the torque converter approaches
the coupling phase because the stator no longer redirects fluid to
increase the flow from impeller to turbine.
When the torque converter reaches coupling speed, the turbine is
traveling at nearly the same speed as the impeller, rotary flow is
much greater than vortex flow, and the torque converter simply
transmits torque like a fluid coupling.
Continued

Stall Speed During converter stall, the impeller rotates but the
turbine does not. This occurs just before the drive wheels of a
vehicle begin to move.
The greatest amount of stall occurs when the engine drives the
impeller at the maximum speed possible without moving the
turbine. The engine speed at which this occurs is called the torque
converter stall speed. When the impeller rotates but the turbine
does not, the speed ratio is zero.
This is the lowest possible speed ratio and the greatest possible
torque multiplication. Most modern torque converters multiply
torque in the range of 2:1 to 2.5:1 at the stall speed.
Continued

Torque Converter Diameter The outside diameter of a torque
converter and the angle of its stator blades determines the stall
speed of the converter.
When both a small and large diameter converter share the same
stator blade angle and turn at the same speed, the smaller converter
creates less centrifugal force to move the fluid inside.
As a result, the small diameter converter has a higher stall speed,
multiplies torque at higher engine speeds, and will not couple until
the engine reaches high speeds.
In comparison, the large diameter converter has a lower stall speed,
multiplies torque at lower engine speeds, and also couples at a
lower engine speed.
Continued

Vehicle manufacturers select torque converters to match the power
train requirements and operating demands of each application.
A vehicle with a large engine that produces a lot of torque at low
RPM will often use a torque converter that couples at low speeds
for greater fuel economy.
Vehicles with smaller engines that produce less torque at low RPM
will use a torque converter that allows the engine to operate higher
in its torque curve, where more power is available.
High-performance vehicles with automatic transmissions use small
diameter converters for the same reason.
Continued

Lockup Torque Converter Even the most efficient torque converters
slip 3% to 6% during operation. This is because the fluid that transmits
torque exhibits a type of slippage known as fluid shear. Fluid shear
creates friction heat, but performs no work when the different layers of
fluid slide past each other.
Eliminating torque converter slippage can improve fuel economy
approximately 4% to 5% during freeway cruising. With increased
emphasis on fuel economy for late-model vehicles, this became
an important goal for automotive engineers.
Lockup torque converters reduce slippage by using a torque converter
clutch (TCC) to lock the impeller to the turbine. Similar to a clutch for a
manual transmission, a TCC uses a friction disc operated by a hydraulic
piston to mechanically
couple the turbine to the impeller. See Figure 100–11
Continued

Figure 100–11 An expanded view of a typical General Motors torque converter clutch (TCC).
Continued

Converter Clutch Control The first hydraulic lockup converters were
controlled entirely by hydraulic pressure and spool valves in the
transmission valve body.
Some later designs added simple electric switches and solenoids to
control pressure to the converter clutch. Late-model hydraulic TCCs use
an electronic control system to regulate the timing and application of the
clutch.
Early hydraulic converter clutches will engage only in high gear because
lockup in the lower gears reduces the torque multiplication needed for
acceleration. Lockup may also be limited to specific vehicle speeds or
operating conditions. For most vehicles, lockup can occur at speeds over
25 to 30 mph (40 to 48 km/h) after the transmission upshifts into high
gear.
Continued

Once lockup occurs, the clutch may disengage automatically during
certain operating conditions such as part- or full-throttle downshift. At
these times, the increased acceleration requirements generally override
the need for better fuel economy.
The more sophisticated electronic control systems can lock and unlock a
converter clutch hundreds of times per minute to meet the vehicle
demands of the moment.
Some recent systems also allow partial lockup of the torque converter.
Traditional lockup torque converters operate either locked or unlocked.
Partial lockup converters allow a regulated amount of slippage at the
clutch.
See Figure 100–12 .
Continued

Figure 100–12 The type of torque converter clutch control determines the type of friction material that is used on a torque
converter clutch. A paper friction material is usually used on clutches that are turned on or off, whereas Kevlar® or carbon
fiber friction materials are used where the clutch is pulse-width modulated.
Continued
CARBON FIBER
KEVLAR ®
PAPER

The summary of torque converter operation is as follows:
Engine speed is low with the vehicle in gear and stopped. At
low engine speeds, automatic transmission fluid does not exert
enough force on to permit the vehicle to move at a creep.
Engine speed increases and vehicle speed starts to increase
As more engine torque is applied to the torque converter, the
torque is transmitted through the movement of the fluid to the
turbine. The stator is locked (prevented from moving) and
redirects the fluid flow back against the turbine. The redirection
of the fluid back to the turbine creates a torque on the turbine
that is greater than the engine torque.
This is called torque multiplication. Most torque converters are
capable of doubling the applied engine torque due to redirection
of the fluid by the stator.
Continued

NOTE: That the torque converter can double torque to the transmission is
the major advantage of using an automatic transmission. A clutch used in a
manual transmission/transaxle can only transmit engine torque.
Engine speed is steady and vehicle speed is steady When the speed of both
the impeller and the turbine reach about the same speed (85% to 90%), the
one-way clutch in the stator unlocks and the stator is free to rotate. This is
called the coupling point.
Vehicle is accelerated rapidly During periods of rapid acceleration, the
engine speed and therefore the impeller speed are a great deal faster than the
turbine speed. The greatest amount of torque multiplication occurs when the
turbine is stopped and the impeller is turning as fast as the engine will turn it.
This speed is called the stall speed.
Continued

Vehicle speed is above 35 mph (55 km/h) and steady
To improve fuel economy, the impeller and the turbine are
mechanically connected by a torque converter clutch (TCC), also
known as a lockup torque converter.
Except for rare cases, the torque converter clutch is applied by the
vehicle computer. The computer senses vehicle speed (VS), engine
load (MAP), and throttle position (TP) and applies the torque
converter clutch.
This lockup can occur in second, third, or fourth (overdrive) gear if
the conditions are right. When the torque converter clutch engages,
the engine RPM usually drops by 150 to 250 RPM.
See Figure 100–13.
Continued

Figure 100–13 A cross-sectional view of a computercontrolled
(modulated) torque converter clutch. The
vehicle computer is capable of pulsing the solenoid
that controls the fluid flow on and off to apply the
torque converter clutch.
Reduction in engine speed
and the elimination of the
normal slippage in the torque
converter improves fuel
economy.
The torque converter clutch
is released during rapid
acceleration for maximum
torque multiplication through
the torque converter for best
acceleration.
Continued

NOTE: The application of the torque converter clutch feels like a normal
shift to most drivers. Therefore, a three-speed automatic transaxle will feel
to many drivers as “shifting” three times (1-2, 2-3, and TCC engagement).
CAUTION: Using a nonstock torque converter is likely to increase
exhaust emissions and decrease fuel economy.

Use a Smaller Diameter Torque Converter for Improved
Performance
A smaller-than-stock-diameter torque converter will not be capable of
absorbing as much torque as a larger (stock) torque converter. As a result, the
stall speed is increased.
Because an engine develops more torque with increased speed (up to a
point), the smaller torque converter will allow the engine to increase to a
higher speed and create more torque to the transmission than would be
capable with the stock torque converter.
This is especially helpful for modified engines because an engine having a
camshaft with increased lift and duration usually lacks low RPM torque. By
using a smaller torque converter, the stall speed is increased to better match
the engine torque.

Automatic Transmission Fluid Cooler The torque converter generates a lot of heat due to the
slippage and torque multiplication that occurs inside. The greatest amount is under a heavy
load with the torque converter clutch is disengaged.
The transmission fluid (ATF) can reach high temperatures (over 250°F [120°C]) very quickly.
This is the reason an automatic transmission fluid cooler is used. Most vehicles use a small
section of the engine radiator to cool the ATF.
The ATF is pumped from the torque converter (greatest source of heat) to the cooler. The ATF
flows through the cooler and returns to the transmission/transaxle to passages that lubricate the
bearings and bushings of the unit. This returned fluid is called lube oil.
See Figures 100–14 and 100–15.
Continued

Figure 100–14 Automatic transmission fluid is routed from the torque converter, where most of the heat in an automatic
transmission is generated, to the radiator, where it is cooled. The cooled fluid then returns to the transmission/transaxle to
lubricate the bearings and bushings.
Continued

Figure 100–15 A cutaway section of a typical radiator showing the automatic transmission fluid cooler. The heat from the
automatic transmission fluid is released to the engine coolant. The engine coolant also warms the automatic transmission
fluid after a cold start.
CAUTION: Because the lube oil uses the ATF flowing from the cooler,
if there is a blockage in the cooler, the transmission/transaxle may not have
enough fluid to properly cool or lubricate the bearings and bushings inside
the unit, leading to wear and eventually premature failure.
Continued

PLANETARY GEAR SETS
In a manual transmission, different gear ratios are obtained by sliding the gears
into mesh. Torque flow must be momentarily interrupted (accomplished by
using a clutch) before the gears are shifted.
With an automatic transmission there is no driver-operated clutch, so gear shifts
are not made by sliding gears into mesh.
Automatic transmissions use a planetary gear set system that does not require
manual gear shifting or an interruption of torque flow to change gear ratios.
Continued

A simple planetary gear set consists of three primary components:
Sun gear
Planet carrier assembly
Ring gear
As discussed in the last chapter, the sun gear gets its name from
its position at the center of the gear set. The planet carrier
assembly holds the pinion gears, also known as planet
gears, which revolve around the sun gear.
The outermost member of the gear set is the ring gear, which
is the internal type with the teeth inside. The pinion gears are
in simultaneous mesh with both the sun and ring gear.
Continued

The pinion gears are free to rotate on pins that are part of the carrier, and
the entire assembly rotates to direct torque flow.
The simple planetary gear set as seen in Figure 100–16 has only two
planet pinions, but most transmission gear sets use three or four.
The pinions are fully meshed with both the sun gear and internal ring
gear at all times.
The planetary gears never disengage to change gear ratios; torque is
simply redirected.
Continued

All gears in a planetary gear set
are in constant mesh.
The torque flow through a
planetary gear set, both input
and output, occurs along a
single axis.
The internal ring gear is
sometimes called an annulus
gear or a ring gear
The planet pinion gears are
often called planet gears or
pinion gears.
The planet carrier assembly is
referred to as the “carrier.”
Figure 100–16 The three members of a simple planetary
gear set are the sun gear, internal ring gear, and planet
carrier assembly.
Continued

Planetary Gear Set Torque Flow In any planetary gear set, each gear always meshes with
several other gears.
Driving one gear will drive all of the other gears as well. This allows the gear set to provide
different gear ratios; depending upon how torque is distributed through the assembly. To
transmit torque through a planetary gear set, a drive member rotates while a second member is
held, which causes a third member to be driven.
Each member of a planetary gear set can play any one of these three roles to transmit torque.
The various combinations of drive, held, and driven members result in the number of gear
ratios available. Certain combinations of drive, hold, and driven can change the direction of
rotation as well.
See Figure 100–17.
Continued

Figure 100–17 To transmit torque
through a planetary gear set, one
(input) member drives, another
(reaction) member is held, and the
third (output) member is driven.
Continued

Torque flows through a planetary gear set in several steps to get from the
drive action of the first member to the driven action of the last member.
The terms “drive” and “driven” simply describe how any two gears work
together. When three or more gears are involved, the second gear is a
driven gear in relation to the first, but a drive gear in relation to the third.
For this reason, the drive member of a planetary gear set is known as the
input member, the held member is the reaction member, and the driven
member is the output member.
See Figure 100–18 for the possible gear ratios and how they are
achieved.
Continued

Figure 100–18 Different modes of transferring torque through a planetary gear set.

Simple Planetary Gear Set Systems A simple planetary gear set system consists of one sun
gear, carrier, and ring gear. A single planetary gear set can provide all of the necessary gear
ratios for a basic automatic transmission.
Using a simple planetary gear set along with a brake band and multiple disc clutch as apply
devices, you can design a two-speed automatic transmission. The transmission provides neutral
and reverse gearing, and performs “low to drive” gear changes
without any input from the driver.
The simple planetary gear set remains the foundation upon which the compound planetary gear
sets used in modern transmissions are built. A simple planetary gear set is often used together
with a compound planetary gear set to provide additional overdrive gearing.
Continued

SIMPSON GEAR SET
A compound planetary gear set system is a configuration that contains more than just the
three basic members of a simple planetary system.
Compound planetary gear sets are capable of providing various combinations of gear
reduction, direct drive, neutral, reverse, and overdrive.
The most popular compound planetary design is the Simpson gear set. Named for its
inventor, the Simpson gear set consists
of two simple planetary gear sets that share a common sun gear.
See Figure 100–19.
Continued

This combination is capable
of providing three forward
gears, as well as neutral and
reverse.
Operation, construction,
and methods of obtaining
various gear ratios with a
simple planetary gear set
also apply to the Simpson
gear set.
The main difference is the
number of gear ratios.
Continued
Figure 100–19 A Simpson planetary gear set is composed of two
ring gears and two planet carrier assemblies that share a common
sun gear.

RAVIGNEAUX GEAR SET
Another popular compound planetary design is the Ravigneaux gear set. The Ravigneaux system has two
sun gears; two sets, one longer than the other, of planet pinions supported in one carrier; and a single ring
gear.
This design provides four forward gears, two in reduction, one direct, and one overdrive, as well as neutral
and reverse. Basic planetary gear set operation, construction, and control methods also apply to the
Ravigneaux gear set.
Both of these compound planetary gear set designs have been used over the years by import and domestic
manufacturers.
See Figure 100–20.
Continued

Figure 100–20 A Ravigneaux gear set is composed of two sun gears, one carrier that supports two sets of pinion gears, and
a single ring gear.
Continued

LAPELLETIES GEAR SET
The Lapelleties (pronounced La-plet-e-ay) gear set was invented by Pierre
Lapelleties, a retired engineer who figured out a unique way to create a simple and
efficient six-speed automatic transmission gear set.
It was first produced by ZF in 2002. The Lapelleties gear set is constructed by
connecting a planetary gear set in front of a Ravigneaux gear set.
Besides ZF, General Motors uses the Lapelleties gear set in the 6L45, 6L50, and
6L90 rear-wheel-drive transmission and Ford uses it in their 6R60, 6R75, and 6R80.
Continued

CONTINUOUSLY VARIABLE TRANSMISSION
A continuously variable transmission (CVT) is usually found on
front-wheel-drive vehicles, which use a transaxle.
Instead of using three or more gears, a continuously variable
transmission uses two variable width pulleys sometimes called variators
to change the gear ratio from about 2.5:1 to an overdrive ratio of 0.5:1.
See Figure 100–21.
Continued

Figure 100–21 The belt-and-pulley CVT uses variable-width pulleys and a special steel belt to provide an infinite number of
speed ratios.
Continued

Purpose and Function The purpose and function of a continuously
variable transmission is to allow the engine to
operate in a speed range where it is most efficient.
Instead of causing the engine speed to vary as the transmission shifts
gears, the engine speed is more constant as the pulleys change to increase
the speed of the vehicle.
The result of using a CVT is improved fuel economy and
reduced exhaust emissions.
Continued

Parts and Operation Most CVT units use a conventional torque
converter with a torque converter clutch except the Honda Civic
CVT. In the Honda Civic CVT, a start clutch is used to apply
engine torque to the drive pulley.
The start clutch slips and provides a small amount of creep until
the driver releases the brake pedal. At this point, the start clutch is
fully applied and transmits torque to the drive pulley.
See Figure 100–22.
NOTE: Some vehicles equipped with a continuously variable
transmission (CVT) have shifter paddles on the steering wheel or a manual
shift mode on the gear selector. When using these paddles to upshift or
downshift, the transmission control module selects preprogrammed ratios,
which give the driver a sense that it is actively shifting gears.
Continued

Figure 100–22 Location of the Honda CVT start clutch.
Continued

CAUTION: With any CVT unit, use of the specified fluid is critical to its
proper operation. Even a little dirt can cause wear to pulleys so be sure to
clean around the dip stick before removing it to check the level of fluid.
The two pulleys are moved at the
same time. One pulley is made
smaller in while at the same time
the other pulley is enlarged.
This change in pulley width allows
the drive chain to move, thereby
changing the rate between the input
and output pulleys.
The chain is pushed rather than
pulled through the pulleys and is
made of hundreds of elements.
Figure 100–23 Honda CVT drive belt
construction.

What Is It Like to Drive a Vehicle Equipped with CVT?
For most, driving a vehicle equipped with a continuously variable transmission (CVT) is the same as driving the same vehicle equipped with a conventional automatic transmission/transaxle.
The vehicle creeps slightly when the brake is released and acceleration when the throttle is opened. Because no shifts occur, the first thing the driver and passenger notice is that it is very
smooth. If the vehicle is equipped with a tachometer, the driver may notice that the engine speed increases when first accelerating and remains higher until speed increases.
During periods of rapid acceleration, the engine speed may be close to its maximum and thereby create noise and vibration often not experienced in a similar vehicle. However, the fuel
economy savings of a CVT compared to a conventional automatic transmission makes the slight difference a reasonable trade-off.

Servicing Continuously Variable Transmissions Routine service of a
continuously variable transmission/transaxle usually involves changing the fluid
at regular intervals.
Always use the exact fluid specified by the vehicle manufacturer. The price of
CVT fluid is several times higher than conventional automatic transmission fluid
but the special additives needed by
a CVT make it critical that the specified fluid be used.
Except for the replacement of the start clutch on a Honda Civic CVT, most
continuously variable transmissions are replaced as an assembly and not
overhauled or repaired.

SUMMARY
1. The torque converter attaches to the engine and transmits
engine torque to the automatic transmission/transaxle
assembly.
2. The torque converter consists of three major components: the
impeller (driving member), turbine (driven member), and the
stator, which helps the torque converter double the available
engine torque at stall speed.
3. Since the early 1980s, a torque converter clutch has usually
been used on most automatic transmissions/transaxles to
increase fuel economy by locking the input and output
members of the torque converter together.
Continued

SUMMARY
4. A typical planetary gear set includes a sun gear in the center
surrounded by planet pinions attached to a planet carrier
assembly and a ring gear on the outside where internal teeth
mesh with the teeth of the planet pinions.
5. Most automatic transmissions/transaxles use a compound
planetary gear set to achieve the various forward gears as well
as reverse.
6. Automatic transmissions/transaxles use compound planetary
gear sets called Simpson or Ravigneaux.
7. Certain members of a gear set must be held to achieve a
particular gear ratio and direction.
(cont.)

end