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Transmissions are found in nearly every
kind of mobile mining equipment.
TABLE OF CONTENTS
INTRODUCTION 04

PAST 04

PRESENT 10

POWERTRAIN COMPONENTS 12

POWERTRAIN COSTS 14

TORQUE CONVERTERS 14

POWERSHIFT TRANSMISSIONS 20

TRANSMISSION CONTROLS 24

CAUSES OF TRANSMISSION REMOVAL 28

HAULING UNIT TRANSMISSIONS 28

CYCLING TRANSMISSIONS 30

DRIVING DOWN COSTS 32

KEYS TO LONG COMPONENT LIFE 33

MEASURING FLUID CLEANLINESS 36

SUMMARY . ..38

IMPROVING COMPONENT DURABILITY f|Q

TABLE OF CONTENTS Uo
Transmissions are found in nearly every kind of mobile mining equipment, and have
two basic functions:
• Transmit power from the engine flywheel to the differential and drive wheels.
• Provide multiple gear ratios to reduce engine flywheel speed and increase
torque to the drive wheels.

The earliest
transmissions were
simple manual
countershaft
transmissions.

The Past
The earliest transmissions were simple manual countershaft transmissions used in track-type
tractors. These transmissions were engaged and disengaged from the engine by use of a hand-
operated clutch lever. Gear selection was made by a manual gearshift. These transmissions
were simple, rugged and dependable. But they were also labor-intensive to shift and required
the operator to stop the tractor to change gears. Manual transmissions were the industry
standard from the earliest days of gasoline powered tractors until the 1950's, when the next
level of technology was introduced.
The next major leap in technology
and productivity occurred with the
introduction of the first powershift
transmission on the D9E track-type
tractor in 1959. The new powershift
transmission was a stunning departure
from the old countershaft concept.

Shifting Gears
Engaging and disengaging the transmission in order to shift gears went from a hand-operated
clutch lever on the first countershaft transmission, to hydraulically-operated clutch packs
which were selected by a simple hand-operated gear selector.

Speed Selection
Changing gear ratios went from manually engaging two shaft mounted gears in the
countershaft transmission to hydraulically engaging one or more planetary gear sets in
the powershift transmission.

DRIVING THE TRACTOR

Always be sure that oil and water are circulating properly before
operating tractor.
To Shift Gears. Disengage flywheel clutch by pushing clutch lever as
far forward as possible, bringing the transmission gears to a stop; then
carefully feel gear shift lever into proper position for speed desired.
The positions are as follows: 02 «•
First Right Rear
Second Left Front - ™™J™| ~
Third Left Rear |
Reverse Right Front ^3 j^
Neutral In Central Position
(the only position where lever may be
moved sidewise freely).
Gear shift lever is held in position by a lock and must be moved a
short distance sidewise before the shift can be made.
When the proper gear are engaged, pull throttle control lever all the
way back. Carefully engage flywheel clutch until slack is taken up be-
tween tractor and load. Then pull clutch lever back sharply so that
it locks the clutch in engaged position.

Shifting instructions from the 1932 Sixty Operating Instructions Book.

IMPROVING COMPONENT DURABILITY |-

INTRODUCTION •>
The new powershift transmission was truly pedal. The gear selector was connected to a low, but directional changes were very
a stunning technological advancement. The spool valve in the transmission control valve frequent. These early powershift transmissions
physically demanding process of engaging body which directed hydraulic pressure to typically had three forward speeds and three
and disengaging the manual clutch and the desired clutch pack. The hydraulic reverse speeds. This type of transmission is
manually shifting gears on the old pressure engaged the clutch pack and known as a "cycling" transmission due to the
countershaft transmission was eliminated. mating planetary gear set, providing the frequent directional changes.
desired gear reduction of engine power.
The new powershift transmission allowed
the operator to change speeds with his Moving the gear selector lever also moved
fingertips with no distraction from operating the position of the spool valve. This directed
the machine. This greatly reduced operator hydraulic pressure to a different clutch pack
fatigue and increased productivity. and engaged it while allowing the previous
clutch pack to drain and disengage.
Gears were selected by simply stepping on
a decelerator pedal to momentarily decrease These transmissions were first used on
engine speed, moving a hand-operated gear track-type tractors, track-type loaders and
selector lever, and releasing the decelerator wheel loaders where travel speeds were
There were many innovations and advancements in powershift technology
in the following years. Another significant improvement came in 1969
with the introduction of the eight-speed powershift transmission on the
621 wheel tractor-scrapers. The first two forward speeds were converter
drive for torque during loading. Speeds 3 through 8 were direct drive for
higher travel speeds. All speeds were manually selected, requiring the
operator to upshift and downshift. This type of transmission is known as
a "hauling unit" transmission due to the multiple forward speeds required
for higher hauling speeds.
The next major step in powershift sophistication and technology came with the introduction The 637 used a 415 horsepower engine on
of the 637 tandem engine wheel tractor-scraper. The 637 used an additional engine and the tractor driving an 8 speed semiautomatic
transmission on the scraper to increase loading power and load capacity. However, the transmission in the front of the machine. The
most significant improvement was the introduction of the first 8 speed semi-automatic scraper contained a smaller 225 horsepower
transmission. The first two forward speeds were converter drive, which were manually engine driving a 4 speed transmission at the
selected by the operator. However, the need to manually shift through the higher travel rear of the machine. The scraper transmission
speeds was eliminated. The operator could select any higher speed from 3 through 8 and was converter drive in all 4 speeds. Each
the transmission would automatically upshift up to the selected speed. Sophisticated speed in the scraper transmission was
transmission control valves monitored both engine and ground speed to provide upshifts matched to two speeds in the tractor
and downshifts at the optimum ground speed. They also prevented the operator from transmission.
accidentally downshifting into an improper gear, which could overspeed and damage the
engine. Hydraulic valves controlled all of the transmission control functions. The 8 speed semi-automatic transmission
in the front shifted independently based on
ground speed. An electrical speed switch
on the front transmission sent a signal to a
corresponding switch on the rear transmission
indicating it's current speed. The rear
transmission used this electrical signal
to select a matching speed.
 8 speed transmission control. Transmission wiring harness.

This was among the most complex and sophisticated of all hydraulic transmission controls
ever used by Caterpillar on any product. The front transmission had a control valve assembly
with four layers of valves containing 44 different spool valves, a hydraulic governor and an
electrical manual switch. The manual switch was operated by transmission linkage, and had
a set of electrical contacts for each transmission speed. The rear transmission contained a
simpler control valve assembly which was shifted by upshift and downshift solenoids. A slave
switch received signals from the manual switch on the front transmission, and controlled
shifting to keep the rear transmission synchronized with the front transmission. The switches
on the transmission were connected by a large multiple section wiring harness which
stretched from the front transmission, across the gooseneck, and a ong the length of the
scraper bowl to the rear transmission.

When operating properly, the performance and productivity of the tandem engine scraper
was unmatched. But the increased complexity from the large number of spool valves and
electrical connections increased the probability of reliability problems. A tiny piece of debris
in the transmission oil could cause a spool valve to stick and prevent the transmission from
shifting. A poor electrical connection or broken wire could result in the rear transmission
being in the wrong gear. The next step in transmission technology was needed to
dramatically improve reliability.

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INTRODUCTION "
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The Present
Modern powershift transmissions still utilize longer requires dozens of spool valves and slippage and wear during engagement.
hydraulic pressure to engage clutch packs a hydraulic governor. Modern transmissions Changes in shift points and clutch
and planetary gear sets. However, the use electronically controlled solenoid engagement can also be easily changed
complexity and unreliability of hydraulic valves to engage and disengage clutch through electronic programming to improve
spool valves and electrical switches is being packs. These electronic valves are capable transmission performance.
replaced by simpler and much more reliable of precisely controlling the rate of clutch
electronic controls. Transmission shifting no engagement and reducing the rate of

The ICM control uses solenoids to upshift and downshift the transmission,
and to operate the torque converter lock-up clutch. Individual modulation
valves for each transmission clutch provide precise clutch engagement.
 Repair Frequency
(Repairs per 100 hours)

There are a number of reasons for this It is also common to think of older transmissions as more reliable and durable before the
dramatic improvement: introduction of electronics. In fact, older transmissions required far more repairs and
adjustments than modern electronically controlled transmissions.
IMPROVED MECHANICAL DESIGN:
Including gears, bearings, and friction Modern electronic powershift transmissions require only about 1/1 Oth the number of repairs
materials. and adjustments per 100 hours of operation than older transmissions with hydraulic controls.
Today's transmissions also last about twice as long between overhauls as early powershift
ELECTRONIC CONTROLS: transmissions.
Virtually eliminate pressure adjustments
and provide much more precise shifting
and controlled clutch engagement.

IMPROVED OILS AND FILTRATION:

Newer oils have more additives to extend
oil life, and improved filters trap harmful
debris in the oil much more effectively.

IMPROVING COMPONENT DURABILIIY *«

INTRODUCTION
Power generated by the engine is transferred from the engine to the rear wheels
through a series of drivetrain components:

^^^^^^^^Q[j^iin^^i POWERTRAIN COMPONENTS

TRANSMISSION CONTROLS
Hydraulically actuated clutches are engaged and disengaged by the transmission control
assembly. Electronically controlled solenoids precisely control the timing and speed of clutch
engagement to provide smooth shifting and long clutch life.

FINAL DRIVES
The final drive assemblies consist of two planetary gearsets
connected together to provide a double reduction in speed and
further increase torque to the drive wheels. Power from the
DIFFERENTIAL differential is transferred through the axle shafts, through the
The differential is a simple, one speed gearbox consisting of a pinion double reduction planetary gears and to the drive wheels. Large
gear and ring gear. The output shaft of the transmission drives the machines use double reduction planetary gearsets, while medium
differential pinion gear. The pinion gear drives the ring gear assembly, and small machines typically use single reduction.
which transfers power to the left and right axle shafts. Differentials
provide a decrease in speed and an increase in torque.
 Each component reduces input speed and
increases output torque to drive the rear wheels.

TORQUE CONVERTER
The torque converter is a fluid coupling which transmits rotating energy from the engine
flywheel to an output shaft which drives the transmission. Increasing the load on the output
shaft causes the speed of the output shaft to decrease and torque to increase.

TRANSMISSION
Semi-automatic powershift transmissions consist of a number of hydraulically actuated
clutches which actuate different gear sets to provide up to 8 different forward speeds.
These different gear ratios further reduce the speed and increase the torque of the
transmission output shaft.

IMPROVING COMPONENT DURABILIIY *Q

POWERTRAIN **
 TORQUE CONVERTERS

Powertrain Costs Torque Converters

The cost to repair and maintain the Torque converters have two basic functions:
transmission and torque converter is LOW SPEEDS
a relatively modest portion of overall Act as a fluid coupling to reduce speed and increase torque between the flywheel
powertrain costs. A typical ratio of and transmission input shaft.
powertrain life cycle costs for a HIGHER SPEEDS
mechanical drive mining truck is: Provide a direct mechanical connection between the flywheel and transmission through
the use of a lock-up clutch in the torque converter.
ENGINE 40%
DIFFERENTIAL & FINAL DRIVES 40% Torque converters are very durable and are rarely the primary cause of downtime. The wear
TRANSMISSION & life of a torque converter is usually longer than one engine life but less than two. Because
TORQUE CONVERTER 10%
torque converters are attached to the rear of the engine, they are usually rebuilt as part of
MISCELLANEOUS 10%
the engine overhaul.

Torque converters consist of four basic parts:

• impeller • Stator
• Turbine • Lock-up Clutch

Cutaway of a torque converter. Torque converter at low speed. Torque converter at higher speeds
with the lock-up clutch engaged.
Converter Drive
During low speed acceleration, high levels of torque are needed to increase machine speed.
The torque converter acts as a fluid coupling to increase torque to the transmission input shaft.

The impeller is mechanically connected to the engine flywheel, and the turbine is connected
to the torque converter output shaft. The impeller is driven by the engine flywheel, and
transfers power from the flywheel to oil in the converter.

Fins on the impeller direct oil at very high force against fins on the turbine. This causes the
turbine and converter torque output shaft to rotate. Power is transferred from the converter
output shaft to the input shaft of the transmission.

The shape of the turbine blade directs oil back to the center of the turbine and into the statoi
The stator has two functions:
• Acts as a reaction hub to significantly increase the efficiency of torque
transfer to the turbine.
• Hedirects oil from the turbine back to the impeller in the same direction of
impeller rotation.

On hauling unit transmissions, converter drive is only used in reverse and forward speeds
1 and 2. On cycling units, converter drive is used in all forward and reverse speeds.

IMPROVING COMI'GNLNI UUHAUILIIY M |-

TORQUE CONVERTERS
Direct Drive
At higher speeds, torque demand decreases and the lock-up clutch is engaged to connect
the impeller to the turbine. This increases driveline efficiency by eliminating the efficiency
losses inherent in fluid couplings. The primary purpose of the lock-up clutch is to increase
drivetrain efficiency in higher speed, low torque operating conditions.

Controlled Throttle Shifting

Controlled throttle shifting is a feature directional clutch. Once the speed and throttle shifting dramatically reduces
used on most electronically controlled directional clutch is engaged, the lock-up clutch wear and drive train shock loading
hauling unit transmissions. It momentarily clutch re-engages and engine power is during full power shifting. This feature is
reduces engine power, disengages the lock- increased. All of this occurs automatically used on an increasing number of loaders
up clutch, then engages the speed and within a fraction of a second. Controlled and track-type tractors.

Sequence of events during controlled throttle shifting.

 A sprag clutch allows the torque converter stator to spin freely in one
direction, but lock-up in the other direction.

Shifting With the Left Pedal

The intended use of the left pedal is to at the tires. The further the pedal is current loaders have eliminated the sprag
disengage the torque converter while depressed, the more the rim pull is reduced. clutch and use the fixed stator exclusively.
maintaining rated engine speed and After depressing the pedal a certain
maximum pump flow for the hydraulics. distance, it begins to act like a brake pedal On the older machines with sprag clutches,
Operators may partially engage the left and applies the service brakes. high idle directional shifts can damage the
pedal while loading the bucket to get more sprag clutch. The use of the left pedal during
engine rpm and hydraulic flow. When the A sprag clutch allows the torque converter directional shifts reduces the stresses on the
left pedal is partially depressed, the impeller stator to spin freely in one direction, but sprag clutch and increases its service life.
clutch pressure is reduced and it begins to lock-up in the other direction. Older loaders
slip. The slippage reduces available rim pull were built with sprag clutches, but most

Shifting With A Decelerator Pedal

Track-type tractors with powershift transmissions have traditionally
used decelerator pedals to reduce engine speed during shifting.
Fully depressing and holding the decelerator reduces engine speed.
Momentarily depressing the decelerator immediately before shifting
reduces engine speed and power and significantly reduces clutch
wear and shock load to the powertrain.

IMPROVING COMPONENT DURABILITY * -|

TORQUE CONVERTERS •'
Torque Converter Wear Parts
Torque converters are very durable and rarely fail before the engine or transmissions. When
they do have problems it is usually caused by excessive internal leakage past the internal
rotating seals or sleeve bearings. The most common failure modes are:
• Lock-up dutch rotating seals
• Lock-up clutch discs
• Other converter rotating seals
• Sleeve bearings

LOCK-UP CLUTCH ROTATING SEALS

• Fail and lower clutch engagement pressure.

LOCK-UP CLUTCH DISCS

• Fail due to excess slippage from low
lock-up dutch engagement pressure.
• Loss of clutch engagement pressure over
time can result from normal spring
relaxation in the pressure control valve,

OTHER CONVERTER ROTATING SEALS

• Allow internal leakage within the
converter which reduces converter
efficiency. Leakage also causes excessive
heat since leakage drains back to the sump
and does not flow through the oil cooler.

SLEEVE BEARINGS
• Support rotating components within the
converter, but also act like seals. As sleeve
wear occurs, internal leakage increases
and causes the same problem as leaking
rotating svals
Primary Causes of Torque
Converter Failure

METALLIC DEBRIS IN THE OIL

• Damages seats and sleeve bearings.

IMPROPER OPERATION
• Failure of the sprag clutch due to misu:
of the neutralize? feature on some whe
loaders.

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Extending Torque Converter Life

KEEP OIL VERY CLEAN AVOID ABUSIVE OPERATION
• Maintaining very clean oil prevents damage to bearings and seals from abrasive • Misuse of the neutralizer feature on
and metallic debris. loaders can cause failure of the sprag
• Even very small magnetic fines in the oil can cause problems. Modern electronically clutch in the torque converter. Full throttle
controlled transmissions use solenoid valves to precisely control shifting and clutch directional shifts cause severe shock
engagements times. The magnetic properties of these solenoid valves attract metallic loading to the entire drivetrain and
fines from the oil which can cause solenoid valves to malfunction. Contamination in eventually result in a major component
the lock-up clutch control valve can cause low engagement pressure or extended failure. It is important for operators to
engagement times. Both of these problems can cause failure of the lock-up clutch due understand that improper operating
to excessive clutch slippage. techniques usually result in premature
failure ofadriveline component and
On some truck applications, the VIMS (Vital Information Monitor System) will monitor lock- significantly increase powertrain
up clutch engagement time. This is done by measuring the time required for clutch output life-cycle costs,
speed to equal input speed during engagement. This is a direct measure of the lock-up
clutch condition and should be monitored periodically along with the engagement pressure, Caterpillar Electronic Control Modules
Specifications for acceptable clutch engagement times are available in the VIMS record and log abusive shift events on all
Application Guide for the specific vehicle. transmissions. Monitoring this data can help
to identify how an operator may be causing
damage to the transmission and drive train
due to abusive shifting.

MPHOVING COMPONFNT DURABILIIY *r

TORQUE CONVERTERS
 POWERSHIFT TRANSMISSIONS

Transmissions Primary Wear Parts

Semi-automatic powershift transmissions Transmissions have only three types of basic wear parts:
consist of a number of hydraulically • Clutch friction and drive discs
actuated clutches which actuate different • Thrust washers
planetary gear sets to provide different • Seals
speeds. Hauling unit transmissions used
in trucks and tractor-scrapers have up Of these, clutches and thrust washers are the primary wear parts
to 8 different forward speeds and 2 which cause must transmission removals.
reverse speeds. Cycling units, used in
wheel loaders and track-type tractors
typically have three forward and three
reverse speeds.
 Clutch Discs and Plates
Most transmissions are removed for overhaul due to anticipated
clutch wear or failure. Actual wearout and failure of clutch drive
plates and discs accounts for a relatively small portion of
transmission overhauls. When a clutch reaches the end of its
normal wear life, most of the friction material has worn away from
the surface of the drive discs. Eventually, slippage occurs between
the drive and driven discs. This slippage produces extreme heat
between the discs, which results in a breakdown of the friction
material and drive discs. The remaining friction material is quickly
lost. The significant loss of friction material produces more slippage
and even higher temperatures, resulting in disc warpage and total
dutch failure.

New bronze thrust Worn bronze thrust New synthetic thrust Worn synthetic thrust Broken synthetic
washer. washer. washer. washer. thrust washer.

Thrust Washers
A secondary cause of transmission removal transmission screen during normal thrust washers and would bo the only
for overhaul is thrust washer wearout maintenance. It may also be detected by source of lead in the oil analysis. Copper
which results in contingent damage to the the transmission sounding unusually noisy is also an element of bronze, but is used
alanetary gearsets. Thrust washers are used during operation. This failure mode seldom elsewhere in the transmission system (oil
to separate the planet gears from the planet results in sudden transmission failure. coolers and support bearings). If the thrust
carrier. Accelerated wear of the thrust washer is synthetic, it will not show in the
washer causes it to become so thin, that it Depending on the thrust washer material oil analysis.
fractures and is expelled from between the jsed, an indication of rapid thrust washer-
planet gear and planet carrier. This allows wear can be detected by SOS oil condition In the event the thrust washer of any
the planet gear to rub against the carrier monitoring prior to the actual failure of the material fails and is no longer present
and wear into it. As the wear progresses, thrust washer. Bronze thrust washer wear between the planet gear and the carrier,
arge amounts of iron wear material are is seen in oil samples as elevated amounts SOS will show an immediate elevation
produced and are usually found in the of copper and lead. Bronze is only used in of iron in the oil.

IMPROVING COMPONFNT DURARIIITY AM

TRANSMISSIONS "
 beais
Both synthetic lip seals and metallic seal
rings are used throughout the transmission
to direct and contain oil pressure. Unless
the transmission oil becomes contaminated
or the transmission is severely overheated,
seals are rarely the cause of transmission
removal.
Metallic seal. Synthetic seal.

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Planetary Gearsets
Each clutch controls a planetary gearset,
which is composed of the following parts:
• Sun gear
• Planet gears
• Plane! carrier
• Ring gear
Planetary gearsets are very reliable and
durable, and normally last through two
or more transmission life cycles before
replacement is required.
Bearings
Roller bearings are used to support rotating
components within the transmission. They
are typically replaced during overhaul.

Shafts
Torque from the engine is transferred from the flywheel, through the transmission input
shaft, to the train of p anetary gearsets in the transmission, to the transmission output shaft.
The gearsets in the transmission provide a range of gear reductions to match output shaft
speed and torque with vehicle operating requirements. Components are attached to the
shafts by means of splines. These splines will wear over time, but normally last through
several transmission life cycles.

IMPROVING COMPOIMFNT DURABILITY MA

TRANSMISSIONS «
 TRANSMISSION CONTROLS

Changes in transmission speed and direction are accomplished hy

engaging selected clutches. Clutch engagement occurs when pressurizec
oil is directed to the clutch piston. Hydraulic force on the clutch piston
causes it to squeeze the friction and drive discs so tightly that they lock
together. The engaged clutch permits the transfer of power through its
planetary gearsets to the transmission output shaft.

The speed of clutch engagement and maintaining adequale engagement

pressure is critical to clutch life and machine performance. The speed
at which this clutch is filled and engagement occurs is called clutch
modulation, Precisely controlled clutch modulation is critical to provide
smooth shifts without excessive clutch slippage. Clutch engagement occurs when
pressurized oil is directed to the
clutch piston.
These functions are performed by the transmission controls. There are
two basic types of transmission controls.
• Mechanical
• Electronic
H*L£^T3i iMJJPi LOSS OF SPRING LOAD
Hn^ Springs relax with age and repeated flexing. Whfin a spi" : iu i uniinl clutch
pressure, loss of spring tension results in a lower prossim; This i JD result in oxtonded
2B^S^^ffi^^Mly clutch engagement times and increased clutch slippage In a semi automatic transmission,
loss of spring tension may also cause shift points to be incorrect
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STICKING SPOOL VALVES

^^Mffll Spring loaded spool valves react precisely to balance hydraulic forces on each end of the

^^22E^^xlS MJM spoel. Small debris in the oil can become lodged in the spool bore clearance and cause the
spool to stick. This was the most frequent cause nf shift problems on older semi-automatic
transmissions,

LACK OF DIAGNOSTICS
Mechanically controlled transmissions offered no diagnostic capabilities. Malfunctions
usually required the serviceman to measure and analyze control and engagement pressures
to determine the problem. Effective troubleshooting required calibrated pressure gauges and
a skilled serviceman with a thorough understanding of system operation.

IMPROVING COMPONENT DURABILITY A|-

CONTROLS "
Electronic Controls
Most powershift transmissions still use springs to control clutch pressure and shift points,
but are rapidly evolving to electronic clutch controls. Electronic transmission controls are far
more reliable and durable than mechanical controls. They also have some built-in diagnostic
capabilities which make troubleshooting much easier. The shift from mechanical to electronic
control lias occurred within three generations of design:

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ELECTRONIC CLUTCH PROPORTIONAL CONTROL (ECPC)
Spring loaded spool valves have been largely eliminated. Fully proportional electronic
solenoid valves control clutch modulation, clutch engagement pressure, directional shifts
and the lock-up clutch in the converter. Proportional solenoid valves convert an electrical
control current from the vehicle Electronic Control Module (ECM) to precisely control
pressure and flow rate. This technology maintains precise control of clutch modulation and
shift points over the life of the transmission. It is far more reliable and durable than
mechanical controls, which utilize spring loaded spool valves.

IMPROVING COMPONFNT DURABILITY Q-J

CONTROLS "
 CAUSES OF TRANSMISSION REMOVAL

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Planned Component
Replacement (PCR)
The vast majority of transmissions are PCR is one of the most common and powerful tools used to reduce unscheduled downtime
removed for overhaul before wearout or and minimize component cost-per-hour. However, overly conservative PCR targets intended to
failure occurs. The number one reason for avoid unscheduled failures altogether may also result in premature overhaul several thousand
transmission removal is Planned Component hours before actual wearout would have occurred. This loss of usable life has the opposite
Replacement, or PCR. A dealer or customer effect of increasing component cost-per-hour.
often anticipates an expected wear life based
an previous product experience. In order to In order to obtain the maximum life and lowest cost-per-hour, some progressive customers
avoid a much more expensive after-failure have adopted a policy of "Run To Full Life". Rather than using a fixed PCR target based on
repair, a Planned Component Replacement past experience, this strategy utilizes prognostic tools such as VIMS and SOS to determine
target is determined. When the PCR target when the maximum amount of actual usable wear life has been obtained.
hours are achieved, the component is
removed for overhaul. The goal of PCR is to
extract the maximum amount of component
wear life, but to overhaul the component
before an actual failure occurs in order to
minimize overhaul cost. Planned Component
Replacement also permits a more efficient
and economical planned repair.
Clutch Failure
The second most common reason for transmission removal is clutch failure.

ELECTRONIC TRANSMISSIONS:
• The primary cause of clutch failure on electronic transmissions is clutch slippage due to
extended shift times. This is caused by electronic shift valves malfunctioning due to
contamination of metallic fines in the oil.

NON-ELECTRONIC TRANSMISSIONS:
* The primary cause of clutch failure on non-electronic transmissions is also clutch slippage
due to extended shift times. The springs which actuate control valve spools lose tension
with age and extended use. This results in a loss of clutch pressures and extended shift
times. Control valve spools may also stick or move slowly due to:
• Very small debris in the oil being caught in the clearance between the spool valve
and its bore.
• Sticking, binding or misadjusted control linkage or cables.

Thrust Washer Wear

The third most common reason for transmission removal is planet
gear thrust washer failure. The cause of accelerated thrust washer
wear is excessive gear side loading. Some amount of side loading
is inherent when two gears run together.

IMPROVING COMPONLN I DURABILITY AQ

CAUSES Ol: REMOVAL "

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Normal Clutch Wear

The most common reason for transmission
removal in cycling unit transmissions is
normal wear of the forward clutch. In the
forward ditection, wheel loaders crowd a
pile to load the bucket while track-type
tractors push a load. In reverse, the wheel
loader is only carrying the loaded bucket,
while the tractor is only carrying its own
weight while repositioning for another
dozing pass. Most loading and dozing
operations also operate in a single speed.
As a result, most clutch wear occurs in the
directional clutches. The forward directional
clutch has a much more severe duty cycle,
and usually wears before the reverse or
speed clutches.
 Clutch Failure
The second most common reason for removal of a cycling unit tmnsmissioM is premature
clutch failure due to excessive oil temperatures. High oil temperatures cause very rapid weai
of clutch friction material, or bonding failure of the friction material to the steel friction disc.
The loss of friction material results in clutch slippage, which produces extreme localized hea
Oil temperature in a failing clutch can exceed 400' F. This heat accelerates failure of the
clutch material and results in disc warpage.

Excessive Oil Temperatures

There are four main causes of excessive oil temperature:

TORQUE CONVERTER STALL

Too much time spent in torque converter stall causes oil temperature in the converter and
transmission to rise very rapidly. Machine overloading and/or high rolling resistance
aggravates this problem.
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EXCESSIVE LEAKAGE
A small amount of internal leakage in the transmission and torque converter is normal.
However, as transmission and torque converter seals and sleeve bearings become heavily
worn, the leakage rate increases. This leakage returns to sump and bypasses the oil cooler.
If the rate of leakage becomes excessive, oil temperatures may become elevated from too
much oil bypassing the oil cooler.

WORN TRANSMISSION PUMP

The transmission pump has abundant flow capacity to provide ample flow to the oil
j^^^^SSBwH&wsSiBi cooler while maintaining desired clutch engagement pressure. If excessive pump wear
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occurs, the reduced flow capacity can result in inadequate clutch engagement pressure
and clutch slippage.

ABUSIVE OPERATION
Full throttle shifts or improper use of the decelerator causes excessive clutch loading
and slippage during engagement. The result is both high oil temperatures and very rapid
clutch wear. Shock loading of the drivetrain may also result in failure of mechanical
driveline components.
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IMPROVING CDMPDNFNT DURABILITY Q<|
J
CAUSES OF REMOVAL '
 DRIVING DOWN COSTS

The key to reducing transmission life cycle costs is to utilize all of the wear life built into
the transmission and e irninate unplanned failures. This often requires some change in both
the way in which a machine is used in production and how it is maintained. Having a basic
understanding of how a powertrain operates and what causes it to wear out and fail is
essential to extending component life.

The practices which maximize component life are quite simple. Quit doing things that cause
components to wear out and fail. A good starting point for transmissions is to review the
primary causes of premature wearout and failure.

PRIMARY CAUSES OF PREMATURE WEAROUT AND FAILURE

Clutches Thrust Washers Seals

Extended engagement time Machine overload Excessive oil temperature
Excessive oil temperature High rolling resistance Metallic debris in the oil
Overload
Abusive operation
KEYS TO LONG COMPONENT LIFE
Manage Payload and Minimize Rolling Resistance
Machine overload and high roiling resistance significantly increases torque loads on drivetrain
components. Excessive torque loads are a primary cause of clutch and thrust washer failure.
a) Use the 10-10-20 rule to avoid excessive payload.
• The actual payioad may exceed the rated capacity by no greater than 10%,
no more than 10% of the time.
• The actual payload may never exceed the rated payioad by more than 20%.
b) Haul roads must be maintained to eliminate steep grades and soft underfoot where
possible. Minimizing ro ling resistance reduces powertrain torque loads and extends
component life.

Proper Operating Practices

Abusive operation can cause excessive temperatures and premature failure.
a) Avoid excessive time in torque converter stall. Excessive stall time quickly overheats the
oil which damages clutches and seals.
b) Avoid improper use of the decelerator pedal on tractors. Full power directional shifts
transfer damaging shock loads through the transmission and drivetrain.
c) Avoid high idle directional shifts to eliminate severe driveline shock loading. This can be
improved with proper use of the left pedal.

Perform Mid-Life Transmission Tune-Ups Clean Lube Oil

Over thousands of hours and mil ions of cycles, springs which control spool valves in the The single most important factor in component
transmission controls can relax and lose tension. This can cause clutch pressure to be low durability is for the component to run in clean
and extend clutch engagement time. This is a leading cause of accelerated clutch wear, lube oil throughout its life. This includes:
a) Inspect transmission filters and screens at PM. Look for any signs of excessive clutch a) Built Clean — Rigid cleanliness standards
material which may indicate accelerated c utch wear. If clutch wear is suspected, check during component rebuild.
operating pressures and clutch engagement times to make sure they are correct, b) Installed Clean — Cleanliness maintained
b} Perform a Mid-Life Transmission Tune-Up. Check and reset transmission operating during installation on the machine.
pressures to spec. This will assure that clutch engagement times are correct and will help c) Operated Clean — Throughout the life
to maximize clutch life. of the component.

Periodic Preventive Maintenance Transmission oil should be maintained at ISO

Diagnosing system condition and monitoring trends is an effective way to identify problems 18/15 or cleaner at all times. Even very small
before they become failures. debris in the oil can cause control valve spools
a) Trucks equipped with a VIMS (Vita! Information Management System) have the capability to stick resulting in excessive clutch slippage
to monitor trends in slip times for each clutch. Excessive siip times usually indicate a clutch and premature failure. The use of high quality
has excessive wear or clutch engagement pressure is low. The VIMS PC program should be transmission filters is critical to trapping and
used periodically to monitor slip trends and identify problems before clutch failure occurs. retaining debris. Transmission screens should
b) The condition of wiring harnesses should a so be checked frequently. A common source also be cleaned and inspected at each PM
of excessive clutch wear is intermittent connections in the wiring harness. This can cause interval to remove debris and assure that
inconsistent signal voltages to transmission shift controls, and result in excessive abnormal wear is not occurring.
clutch slippage.

IMPROVING COMPONENT DURABILITY Q«J

COMPONENT LIFE **
Electronic transmissions usually have two levels of filtration.

LUBE CIRCUIT: CONTROL CIRCUIT:

Gil from the transmission lube pump is user Oil from the transmission control pump is used to operate the control valves and actuate the
to cool and lubricate all of the gears, transmission clutches. Control oil is finely filtered by a high efficiency six-micron filter. This
bearings, and clutches in the transmission. level of filtration is necessary to remove very small metallic fines that are attracted to the
Lube oil is filtered by a 25 micron filter. This magnetic field of the solenoid valves and can cause the valves to malfunction.
relatively coarse filter is used in order
to trap clutch debris without prematurely
plugging during the normal 500 hour PM
interval. Filter plugging from clutch friction
disc material is most likely 10 occur during
the initial break-in period on a now or
rebuilt transmission

Keeping Oil Clean OFF-BOARD FILTRATION

There is a rapidly growing realization by customers worldwide that maintaining very clean The use of off-board filtration carts during
oil improves component reliability and durability. This is driving a demand for better filtration. PM has gained wide acceptance. The carts
Currently there are two methods to improve oil cleanliness during operation. contain air or electric pumps which draw
oil from the component on the machine
and pass it through a large, High Efficiency
filter on the cart, then return it to the
machine. Oil continues to circulate until it
reaches a target cleanliness while other PM
activities are being performed. Because the
component is not running and continuing
to generate debris, the off-board filtration
process can clean the oil to very high levels
for the start of the next PM period. In some
applications, the onboard filtration on the
machine is not capable of removing
contaminants as fast as they are generated.
This allows the oil to become increasingly
contaminated as the machine continues
to operate. The off-board filtration process
removes the excess contaminates when it
is repeated during the next PM. The net
effect is that the average cleanliness of the
oil is much better over time and component
life is improved.
ON-BOARD FILTRATION
Fluid Filters
Oil cleanliness may be improved in some applications simply by using
finer micron filters in onboard circuits. In one documented case,
replacing the 25 micron filter on the transmission charging circuit
with a six micron filter improved average oil cleanliness tc
approximately 16/13. However, switching to finer filters may cause
initial filter plugging during the PM period as large amounts of small
debris are trapped in the finer filters. The plugged filter should be
replaced and the machine placed back into service. Experience has
shown that this usually occurs only once or twice before the oil
cleans up and the finer filters last the duration of the PM period.

Breather Filters
Breather filters may be another source of contamination in dusty
applications where dust particles are extremely fine. Very small dust
particles may pass through standard breather filter media and
contribute to system contamination. Some customers have
effectively eliminated this problem by replacing standard breather
filters with a High Efficiency fuel filters, (filtershown left)

IMPROVING COMPONENT DURABILITY t\r

COMPONENT LIFE ^
 MEASURING FLUID CLEANLINESS

The term "clean oil" is a relative term ISO Standards

depending on the type of oil and where it Hydraulic and lube oil cleanliness is generally
is used. There are several types of oil used expressed in terms of an ISO rating. This refers
on Caterpillar machines in various systems. to the International Standards Organization
Different components and circuits generate Standard 4406, which classifies fluid
different amounts and types of debris. :leanliness by the number and size of particles
The first step is to determine how the in a certain quantity of fluid. Particle size
cleanliness of fluids is measured. is measured in microns, which are very small.
A micron is one millionth of a meter or
4/100,000 of an inch.
• A human hair is shout 4/1,000 of an inch
or WO microns in diameter
• The smallest particle which can be seen
by the human eye is about 40 microns.

ISO Size Categories

The ISO system uses a series of three particle
size categories to identify the approximate
number of particles of three different sizes
which are present in one cubic milliliter of oil.
The three ISO particle size categories are:
The number of particles greater in diameter The number of particles of each size are categorized in ranges shown in the chart. Notice that
than; each range is twice the size of the range that precedes it. The most common ranges used to
4 microns express oil cleanliness are usually from 13 to 24.
6 microns
An example of dirty oil would be 21/19/17. This would contain the following:
14 microns+ PARTICLE SIZE ISO RANGE NUMBER OF PARTICLE IN 1 ML
4 microns 21 10,000-20,000
6 microns 19 2,500-5,000
14 microns 17 80-160

An example of very clean oil would be 18/16/13

PARTICLE SIZE ISO RANGE NUMBER OF PARTICLE IN 1 ML
4 microns 18 1,300-2500
6 microns 16 320-640
14 microns 13 40-80

With thin fluids which contain large amounts of very small particles, such as diesel fuel,
Caterpillar uses all three numbers in the ISO code. However, on thicker viscosity hydraulic
and lubricating fluids, the number of very small particles is less important. Fluid cleanliness
is usually expressed using only the two larger particle sizes. As an example, 18/16/13
would be stated as simply 16/13.

What Is Clean Oil?

"Clean oil" is a somewhat relative term, depending on the viscosity of the fluid and the The oil in a compartment may be cleaned by
system in which it is used. Each system generates a different amount of debris between any of three methods:
service intervals. The following are typical examples of "clean oil" after PM 1) Draining dirty oil and replacing
service has been performed: with new oil
2) Filtering with onboard filtration
NEW ENGINE OIL 18/15
3) Filtering with off-board filtration
FILTERED TRANSMISSION FLUID 16/13
(kidney-looping)
REAR AXLE 18/15
HYDRAULIC SYSTEM (WITHOUT BRAKES) 16/13
HYDRAULIC SYSTEM (WITH BRAKES} 18/15

IMPROVING CQMPUNhNI DURABILITY «-j

FLUID CLEANLINESS **
SUMMARY
Much has changed since the days of the first track-type tractors There is also a growing trend to stretch the useful lives of some
and the manual countershaft transmissions. Today's machines are: machines to as long as 100,000 hours. All of these changes are
• Much bigger the result of intense competition in the mining industry to
• More complex & sophisticated maximize productivity and drive down cost per ton. In order to
• More productive remain competitive, it is absolutely essential to utilize all of the
• More reliable & durable value built into powertrain components.
• Much less expensive to operate in cost per ton

Outdated operational practices lead

to higher wear rates, shorter component
lives, and much higher component life
cycle costs. The greatest opportunity
for cost savings lies in effectively
utilizing the life and value
already built into the machine.
 IMPROVING COMPONENT DURABILITY

This series of high quality booklets contains full-color graphics and easy-to-understand
explanations of the main causes of wear and failure in major system components. Special
attention is given to practices which cause accelerated wear, and how to dramatically
improve component life in many applications. (Available in paper only/packages of 10)

FINAL DRIVES & FUEL SYSTEMS COMPONENT REMOVAL

DIFFERENTIALS SENR9620-01 & INSTALLATION
SEBF1015 ENGLISH/ 32 PAGES SEBF1017
SSBF1015 SPANISH 24 PAGES
40 PAGES

IMPROVING COMI'CMNI UUHAUILIIY «Q

OTHER RESOURCES ^"