Chapter 16
Standard Transmission
Servicing
Objectives (1 of 2)
• Explain the importance of using the correct
lubricant and maintaining the correct oil level
in a transmission.
• List the preventive maintenance inspections
that should be made periodically on a
standard transmission.
• Explain how to replace a rear seal.
• Describe the procedure for troubleshooting
standard transmissions.
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 failure
analysis on transmission components.
• Troubleshoot an air shift system.
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.
Mineral-based Lubes
• Initial oil change
– Will flush out of the transmission any cutting debris
created by virgin gears meshing
– Linehaul
• Any time after 3,000 miles, but before 5,000 miles
– Off-highway
• After 24 and before 100 hours of service
• Oil change intervals
– Linehaul: Oil change intervals vary between 50,000
and 100,000 miles for linehaul applications.
– Off-highway: Off-highway operation usually requires
oil change intervals ranging from 1,000 hours to a
maximum of 2,000 hours of service.
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 maximize
transmission service life, can be eliminated.
• E-250: E-250 lubricant is rated for 250,000
linehaul miles.
Caution
• Do not add transmission lubricant without first
checking what lubricant the transmission is
using.
• Mineral-based gear oils, mineral-based
engine oils, and synthetic gear lubes are all
approved for use in transmissions and none
of them are particularly compatible. Mixing
transmission oils causes accelerated lube
breakdown, resulting in lubrication failures.
Checking Oil Level
• Check at each A-type
service, typically at intervals
of 5,000 or 10,000 highway
miles.
• Avoid mixing brands,
weights, and types of oil.
• The transmission oil level
should be exactly even with
the filler plug opening as
shown.
– Overfilling can cause oil
aeration.
– Under-filling results in oil
starvation.
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 level
by dipping your finger into the oil filler hole is
not a good practice.
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.
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.
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.
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 problems
such as hard shift or jumping out of gear.
B Inspection PM
• Air control system
– Check for leaks.
• Bell/clutch housing flange
– Check fastener torque.
• Clutch shaft yoke bushings
– Grease clutch shaft bushings
lightly.
– Pry upward on the shaft to
check for wear.
• COE remote shift linkage
– Lube U-joints and check for
wear.
– Check any bushings in the
linkage 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 proper
torque.
– Tighten if necessary.
• Output shaft assembly
– Pry upward on the output
shaft to check radial play in
the mainshaft rear bearing.
– Check the splines on the
output shaft for wear from
movement and chucking
action of the U-joint yokes.
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 oil
change intervals that are better suited to the actual operating
condition 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.
Preventive Maintenance
Recommendations
• See Table 16-1 on page 469 of the textbook.
Caution
• Using a 1-inch air gun to tighten yoke retaining nuts
should be avoided, although it is all right to remove
the 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 thoroughly
clean the fasteners and their mating threads before
reinstalling.
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 to
operating temperatures, it expands to occupy
a greater volume. If the breather is plugged,
this can cause seal failure.
Rear Seal Replacement
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 the
seal or draw in contaminants.
Caution
• Do not over-torque the yoke nut, which can
damage the bearing.
• Do not perform this operation using a 1-inch
air gun.
Shop Talk
• Wear rings that increase the original yoke
diameter can cause the new seal to wear
more rapidly due to increased seal lip
pressure.
Transmission
Troubleshooting Guidelines
• See Table 16-2 on pages 476-477 of the
textbook.
Towing Precautions
Caution
• When the driveline or axle shafts are
reinstalled:
– The axle nuts must be tightened to the correct
torques (Refer to the specific service manual
for the correct torque values.)
– The axle shafts properly installed (RH and LH)
– The drive shafts properly phased
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.
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 today’s 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.
Analysis of Bearing Failures
• Fretting
– The bearing outer race can
pick up the machining pattern
of the bearing bore.
– It can be mistakenly
diagnosed as one that has
spun in the bore.
• Contamination
– Scoring, scratching, and
pitting of bearing contact
surfaces identify
contamination failures.
– It is caused by very fine
particles suspended in the
lubricant or by the use of older
EP (extreme pressure) oils.
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 until
ready for installation.
Timing Transmissions
• Multiple countershaft transmissions must be timed during
assembly.
• Timing ensures that the countershaft gears contact their mating
mainshaft 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 this
chapter:
– In the main section, it is necessary to time only the drive gear
set.
– In the auxiliary section, depending on the model, only the low
range, deep reduction, or splitter gear sets have to be timed.
Timing the Front Section (1 of 2)
• Before placing each
countershaft 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.
Timing the Front Section (2 of 2)
• Mark the two adjacent teeth
located directly opposite the
first set marked on the main
drive gear.
– There should be an equal
number of unmarked gear
teeth on each side
between the marked teeth.
• After the mainshaft and
countershaft are installed
into the housing, the marked
teeth should be meshed
exactly as shown.
Timing the Auxiliary Section (1 of 2)
• The specific gears on the
mainshaft 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 located
directly opposite the first
set marked.
Timing the Auxiliary Section (2 of 2)
• Mark the tooth stamped with
an “O” on gear to mate with
timed the mainshaft gear.
• Install the mainshaft gear in
position on the range
mainshaft or output shaft.
• Place the auxiliary
countershaft assemblies into
position and mesh the marked
teeth of mating countershaft
gears with the marked teeth of
the mainshaft gear.
• Fully seat the rear bearings on
each countershaft to complete
the installation.
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 rotating
components contact, pick up, and circulate oil
from the oil in the sump.
– Maintaining the correct oil level is critical for
splash lubrication to be effective.
Summary (2 of 6)
• Only lubricants recommended by the
transmission manufacturer should be used in
a transmission.
– These could be either gear or engine oils.
• It is usually recommended that the first oil
change be performed shortly after the
transmission enters service, often between
3,000 and 5,000 miles of operation in a
linehaul application, or less in vocational
service.
Summary (3 of 6)
• In general linehaul application, it is good
practice 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.
Summary (4 of 6)
• Leakage in transmission rear seals is a
relatively common problem in truck
transmissions, but one that is easily repaired.
• When diagnosing transmission complaints, it
is important that you confirm that the
transmission is the actual cause of the
problem before removing it for repair.
Summary (5 of 6)
• When disassembling a transmission, each
component should be carefully inspected for
abnormal wear and damage.
– Components that are not reusable should be
ordered 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.
Summary (6 of 6)
• Bearing failures occur because of dirt
contamination and poor lubrication.
– More than 90 percent of bearing failures are
caused by dirt.
– Cleanliness is critical when repairing and
servicing standard transmissions.