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Objectives (2 of 2)
Identify the causes of some typical
transmission performance problems, such as
unusual noises, leaks, vibrations, jumping out
of gear, and hard shifting. Outline the procedure for overhauling a
transmission.
Analyze the procedure for performing failureanalysis on transmission components.
Troubleshoot an air shift system.
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Recommended Lubricants
Recommended lube Use only the recommended lube.
Synthetic lube Most transmission manufacturers today prefer synthetic
lubricants.
E-500 Eaton recommends E-500 lubricant. It is designed to run
500,000 linehaul miles with no initial drain interval required.
E-250 Lubricant is rated for 250,000 linehaul miles before a change is
required. Synthetics exceed requirements They can be expected to perform effectively through various
geographic and seasonal temperature conditions.
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Synthetic-based Lubes
E-500: E-500 is designed for 500,000
linehaul miles.
Initial drain: The initial drain interval, once
considered so important to maximizetransmission service life, can be eliminated.
E-250: E-250 lubricant is rated for 250,000
linehaul miles.
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Checking Oil Level
Check at each A-typeservice, typically at intervalsof 5,000 or 10,000 highwaymiles.
Avoid mixing brands,weights, and types of oil.
The transmission oil levelshould be exactly even withthe filler plug opening asshown.
Overfilling can cause oilaeration.
Under-filling results in oilstarvation.
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Shop Talk
Transmission oil should be exactly level with
the filler plug opening.
One finger joint equals approximately one
gallon of transmission oil, so testing oil levelby dipping your finger into the oil filler hole is
not a good practice.
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Caution
Do not overfill the transmission.
Overfilling usually results in oil breakdown due
to aeration caused by the churning action of
the gears. Premature breakdown of the oil will result in
varnish and sludge deposits that plug up oil
ports and build up on splines and bearings.
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Shop Talk
When draining transmission oil, check for
metal particles in the oil.
Metal particles may indicate excessive wear
and may warn of an imminent failure.
It is not unusual for a newly broken in
transmission to have minute metal particles
held to a magnetic drain plug.
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Preventive Maintenance Inspections
Preventive maintenance (PM) can help avoid failures,
minimize vehicle downtime, and reduce the cost of repairs.
Often, transmission failures can be traced directly or indirectly
to poor maintenance.
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Daily Maintenance
During the drivers daily pre-trip:
Air tanks
Drain air tanks to remove water or oil.
Oil leaks
Visually check for oil leaks.
Shifting performance
Report any shifting performance problemssuch as hard shift or jumping out of gear.
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B Inspection PM
Air control system Check for leaks.
Bell/clutch housing flange Check fastener torque.
Clutch shaft yoke bushings
Grease clutch shaft bushingslightly.
Pry upward on the shaft tocheck for wear.
COE remote shift linkage Lube U-joints and check for
wear. Check any bushings in thelinkage for wear.
Air filter Check and clean or replace
the air filter element.
Transmission output yoke Uncouple the U-joint and
check the flange nut for propertorque.
Tighten if necessary.
Output shaft assembly Pry upward on the output
shaft to check radial play inthe mainshaft rear bearing.
Check the splines on theoutput shaft for wear frommovement and chuckingaction of the U-joint yokes.
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C Inspection PM
Oil life If an oil change is required, drain and refill the transmission with the
specified oil.
Transmission oil analysis can be used to establish more precise oilchange intervals that are better suited to the actual operatingcondition of the truck.
Gearshift lever Check for bending and free play in the tower housing.
Oil shift tower assembly Remove the air lines at the slave valve and remove the shift tower from
the transmission.
Check the tension spring and washer for wear and loss of tension.
Check the gearshift lever spade pin/shift finger for wear. Also take a look at the yokes and blocks in the shift bar housing,
checking for wear at all critical contact points.
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Caution
Using a 1-inch air gun to tighten yoke retaining nutsshould be avoided, although it is all right to removethe nut using this tool.
Many fasteners are bored completely through the
housing. These fasteners must have thread sealant applied to
the threads.
If oil leakage is observed at the PTO covers,
replace the PTO cover gaskets and thoroughlyclean the fasteners and their mating threads beforereinstalling.
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Shop Talk
Always check for a plugged transmission
breather when identifying the cause of a
transmission oil leak.
When transmission oil is raised from cold tooperating temperatures, it expands to occupy
a greater volume. If the breather is plugged,
this can cause seal failure.
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Rear Seal Replacement
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Shop Talk
Do not attempt to repair a visibly worn or
damaged yoke by polishing it with crocus
cloth.
Minor scratches can either track oil under theseal or draw in contaminants.
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Caution
Do not over-torque the yoke nut, which can
damage the bearing.
Do not perform this operation using a 1-inch
air gun.
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Transmission
Troubleshooting Guidelines
See Table 16-2 on pages 476-477 of the
textbook.
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Towing Precautions
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Caution
When the driveline or axle shafts are
reinstalled:
The axle nuts must be tightened to the correct
torques (Refer to the specific service manualfor the correct torque values.)
The axle shafts properly installed (RH and LH)
The drive shafts properly phased
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General Transmission
Removal Practices Caution
Ensure that the transmission does not hang by
the input shaft in the pilot bearing bore in the
flywheel. The clutch assembly, pilot bearing, and input
shaft can be damaged if the transmission is
supported by the input shaft.
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Shop Talk
Engine torsionals refers to the frequency of
torsional pulses delivered to the drivetrain as
the force of each cylinder power stroke is
unloaded into the crankshaft. Because of todays practice of managing
engines at slower speeds and higher torque to
produce better fuel economy, lower frequency
torsionals are produced and this has caused
some transmission failures.
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Analysis of Bearing Failures
Fretting The bearing outer race can
pick up the machining patternof the bearing bore.
It can be mistakenlydiagnosed as one that hasspun in the bore.
Contamination
Scoring, scratching, andpitting of bearing contactsurfaces identifycontamination failures.
It is caused by very fineparticles suspended in thelubricant or by the use of olderEP (extreme pressure) oils.
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Shop Talk
Store new bearings in their shipping
wrappers until ready for use.
Used bearings should be cleaned in solvent,
lubricated, and wrapped in greasy paper untilready for installation.
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Timing Transmissions
Multiple countershaft transmissions must be timed duringassembly.
Timing ensures that the countershaft gears contact their matingmainshaft gears in phase to properly distribute the torque load. When timing a transmission, follow the OEM procedure.
In the typical truck transmission used as an example in thischapter: In the main section, it is necessary to time only the drive gear
set.
In the auxiliary section, depending on the model, only the lowrange, deep reduction, or splitter gear sets have to be timed.
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Timing the Front Section (1 of 2)
Before placing eachcountershaft assembly into
the housing, mark the tooth
located directly over the
keyway of the countershaft
drive gear.
In many transmissions,
you might find that this
tooth is stamped with an
O to identify it.
Mark any two adjacent teeth
on the main drive gear.
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Timing the Auxiliary Section (1 of 2)
The specific gears on themainshaft and countershafts
that must be marked differ,
depending on the auxiliary
gearbox design.
Mark any two adjacent teeth
on the mainshaft gear of the
set to be timed.
Then mark the two
adjacent teeth locateddirectly opposite the first
set marked.
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Timing the Auxiliary Section (2 of 2)
Mark the tooth stamped withan O on gear to mate withtimed the mainshaft gear.
Install the mainshaft gear inposition on the range
mainshaft or output shaft. Place the auxiliary
countershaft assemblies intoposition and mesh the markedteeth of mating countershaftgears with the marked teeth of
the mainshaft gear. Fully seat the rear bearings on
each countershaft to completethe installation.
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Summary (1 of 6)
Scheduled lubrication services are key to a
good transmission maintenance program.
Standard transmissions depend on splash
lubrication, meaning that some of the rotatingcomponents contact, pick up, and circulate oil
from the oil in the sump.
Maintaining the correct oil level is critical forsplash lubrication to be effective.
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Summary (2 of 6)
Only lubricants recommended by thetransmission manufacturer should be used ina transmission.
These could be either gear or engine oils.
It is usually recommended that the first oilchange be performed shortly after thetransmission enters service, often between
3,000 and 5,000 miles of operation in alinehaul application, or less in vocationalservice.
S
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Summary (3 of 6)
In general linehaul application, it is goodpractice to schedule a transmission oil
change from 50,000 to 100,000 miles of
service. Good preventive maintenance (PM) lowers
the incidence of breakdowns, minimizes
downtime, and reduces the cost of repairs.
S
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Summary (4 of 6)
Leakage in transmission rear seals is arelatively common problem in truck
transmissions, but one that is easily repaired.
When diagnosing transmission complaints, itis important that you confirm that the
transmission is the actual cause of the
problem before removing it for repair.
S
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Summary (5 of 6)
When disassembling a transmission, eachcomponent should be carefully inspected for
abnormal wear and damage.
Components that are not reusable should beordered after disassembly, not discovered
during reassembly.
Ensure that a cause of failure is determined
before reassembly, or the failure is likely to
recur within a short period.
S
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Summary (6 of 6)
Bearing failures occur because of dirtcontamination and poor lubrication.
More than 90 percent of bearing failures are
caused by dirt. Cleanliness is critical when repairing and
servicing standard transmissions.