Transcript Chapter 19 Automatic Transmission Maintenance

Chapter 19
Automatic Transmission
Maintenance
Objectives (1 of 3)
• Perform hot and cold transmission oil level
checks.
• Identify the types of hydraulic fluid used in
truck automatic transmissions.
• Change automatic transmission oil and filters.
• Inspect transmission oil for signs of
contamination.
Objectives (2 of 3)
• Adjust the manual gear selector linkage,
mechanical modulator control linkage, and air
modulator control on a truck automatic
transmission.
• Perform a transmission stall test.
• Perform engine speed and vehicle speed
shift point tests.
Objectives (3 of 3)
• Describe basic transmission test stand
procedure.
• Test the transmission valve body.
• Summarize some basic inspection and
troubleshooting procedures for automatic
transmissions.
Low Oil Level
• Air enters the system
– When the transmission oil level is low, oil will not completely
cover the oil filter. This pulls air into the pump inlet along with oil
that is then routed to the clutches and converter.
• Aeration
– The result of air in the hydraulic system is known as aeration.
Because air is compressible, it severely affects the operation of
the hydraulic system. The effects can be:
• Converter aeration
• Irregular shifting
• Overheating
• Poor lubrication
– Aeration of transmission oil alters its viscosity and changes its
appearance to that of a thin, milky liquid.
Shop Talk
• It should be noted that a defective oil filler
tube seal ring will allow the oil pump to draw
air into the oil from the sump, which will result
in aeration of the oil.
High Oil Level
• Oil level should be below the rotating components.
– At normal oil levels, the sump oil level should be slightly below
the planetary gearsets.
– When the oil level is maintained above the FULL mark on the
dipstick, the oil level in the sump rises so that the planetary
gears run in oil, a condition that can cause foaming and
aeration.
• Aerated transmission fluid results in:
– Converter aeration
– Irregular shifting
– Overheating
– Poor lubrication
• If accidental overfilling occurs during servicing, the excess oil
should be drained.
Interpreting Oil Level Readings
• Engine speed and oil temperature significantly
affect the oil level.
• Both cold and hot level checks should be taken.
– A cold level check is required to ensure there is
sufficient oil in the transmission until normal operating
temperature is reached.
– The hot check is made when the transmission oil
reaches normal operating temperature (160°F–
200°F) and is the more reliable of the two checks.
Caution
• You should check the transmission oil level at least
two times to ensure that an accurate reading is
made.
– If the dipstick readings are inconsistent (some high,
some low), check for proper venting of the
transmission breather or oil filler tube. A clogged
breather can force oil up into the filler tube and cause
inaccurate readings. If the filler tube is unvented, the
vacuum produced will cause the dipstick to draw oil
up into the tube as it is pulled from the tube. Again,
the result will be an inaccurate reading.
Shop Talk
• The REF FILL (COLD RUN) level is an
approximate level and can vary with specific
transmissions.
• To ensure proper operating levels, a hot oil
level check must be performed.
Allison Dipstick
Hot Check
• The oil temperature should be between 160°F and
200°F to make this test.
• With the engine at idle and the transmission in
neutral, wipe the dipstick clean and check the oil
level.
– If the oil level registers in the HOT RUN band
(between ADD and FULL), the oil level is correct.
– If the oil level registers on or below the bottom line of
the HOT RUN band or the ADD line, add oil to bring
the level to the middle of the band.
• Note that one quart of oil will raise the level from the
bottom of the band to the top of the band in most
transmissions (from the ADD line to the FULL line).
Hydraulic Fluid Recommendations
• Automatic transmission
manufacturers may
recommend:
– Dexron, Dexron II, Dexron III,
or Type C-4 (ATD-approved
SAE 10W or SAE 30)
• Off-highway
– Type C-4 fluids are the only
fluids usually approved for use
in off-highway applications.
• Above 86°F
– Type C-4 SAE 30 is specified
when the ambient temperature
is consistently above 86°F.
– Some but not all Dexron II
fluids also qualify as type C-4
fluids.
• C-4 compatibility
– Check that the materials used
in auxiliary equipment such as
tubes, hoses, external filters,
and seals are C-4-compatible.
• TranSynd
– Allison currently recommends
the use of TranSynd synthetic
oil in all their transmissions.
TranSynd can extend oil drain
intervals by three times.
Cold Startup
• Don’t operate cold.
– The transmission should not be operated in forward or
reverse gears if the transmission oil falls below a
certain temperature.
– Minimum operating temperatures for recommended
fluids are as follows:
•
•
•
•
TranSynd -10°F
Dexron (I, II or III) -10°F
Type C-4 SAE 10W 10°F
Type C-4 SAE 30 32°F
• Preheat
– When the ambient temperature is below the minimum
fluid temperatures listed, preheat is required.
Caution
• Containers or transfer devices that have
been used for engine coolant solutions must
not be used for transmission fluid.
• Antifreeze contains ethylene or propylene
glycol, which, if introduced into a
transmission, can cause the clutch plate to
fail.
Governor Filter Change
• Allison recommend that the
governor filter be inspected
or replaced at every oil/filter
change.
• A pipe plug can be used to
retain the governor oil
screen in older model
Allison transmissions, as
shown.
• If it is undamaged, clean it in
mineral spirits and reinstall
it. If it is damaged, replace
it. Install the filter open end
first into the transmission
cover and reinstall the pipe
plug.
Metal Particles
• Metal particles in the oil or on the magnetic drain
plug (except for those minute particles normally
trapped in the oil filter) may indicate transmission
damage.
• When larger metallic particles are found in the
sump, the transmission should be disassembled
and inspected to locate the source.
• Beyond locating the cause, metal contamination
requires a complete disassembly of the
transmission and cleaning of all internal and
external circuits, cooler, and all other areas where
the particles could lodge.
Coolant Leakage
• Engine coolant damages transmissions.
• Remove all traces.
– The transmission should be disassembled, inspected,
and cleaned.
• Test kits
– Test kits can be used to detect traces of glycol in the
transmission oil.
• You should note, however, that certain additives in some
transmission oil can produce a positive reading.
• In the event of questionable test results, therefore, use a
lab analysis of the oil.
Auxiliary Filters
• After a transmission failure
– An auxiliary filter may be installed in the cooler return
line after debris or dirt has been introduced into the oil
system because of failure.
• Avoid a repeat failure
– The auxiliary filter, which should be installed before
the vehicle is placed back in service, prevents debris
from being circulated into the transmission and
causing a repeat failure.
• Most auxiliary oil filters are changed 5,000 miles
after their initial installation and at regular oil
change intervals thereafter.
High-efficiency Filters
• They are available for older transmissions.
• They have no mileage limitations, but when used on
older transmissions, they should be changed when
they become clogged or at three-year intervals,
whichever occurs first.
• They have a differential pressure switch that
monitors pressure drop across the filter. It triggers a
dash-mounted warning light.
• Allison does not recommend the use of extended
service high-efficiency filters on any WT
transmissions.
External Lines and
Oil Cooler Inspection
• Look for leaks
– Inspect all lines for loose or leaking connections, worn or
damaged hoses or tubing, and loose fasteners.
• Oil in the coolant
– Examine the radiator coolant for traces of transmission oil. This
condition may indicate a defective heat exchanger.
• High operating temperatures
– Extended operation at high operating temperatures can cause
clogging of the oil cooler and can lead to transmission failure.
• Oil cooler
– The oil cooler system should be thoroughly cleaned after any
rebuild work is performed on the transmission.
Transmission Oil Myths (1 of 3)
• Myth 1–Oils are interchangeable.
– Additive packages in lubricants made by
different companies vary.
– Two oils with the same viscosity and basic
properties can have additives packages that
can conflict and result in breakdown.
– Some synthetic oil additives are incompatible
with mineral base stocks; therefore, with
Allison, check if you are swapping from one to
the other.
Transmission Oil Myths (2 of 3)
• Myth 2–Oil never wears out.
– Oxidation limits the life of transmission oils,
and the extent to which the oil is oxidized
depends on running temperatures.
– Oil begins to oxidize at 65°C and, for each
10°C rise above that temperature, oil life is
reduced by half.
Transmission Oil Myths (3 of 3)
• Myth 3–Snake oil additives improve
lubrication.
– Major OEMs have extensive research and
engineering capabilities when proofing
lubricants and precisely balance the additive
package to maximize operational life.
– Tampering with the additive package by
dumping in additives of unknown chemistry
unbalances the oil and can result in premature
failure.
Caution
• Stall tests are usually specified for 15
seconds.
• Full stall should never be run for a period
exceeding 30 seconds at any one time
because of the rapid rise in oil temperature.
• Converter-out temperatures should not
exceed 300°F.
• If the stall test has to be repeated, allow for a
cool-down period. Monitor the engine
temperature as well.
Warning
• To perform a transmission stall test, both the
vehicle parking and service brakes should be
properly adjusted and fully applied.
• The wheels over at least two axles must be
chocked as an extra precaution. It also
makes sense to chain the vehicle to the floor
anchors. No one should stand either in front
of or behind the vehicle during the test.
Stall Test Results
• Because of operating condition variables, stall speed deviations
of up to 150 rpm from specification can be viewed as within
normal range.
– Over 150 rpm low = Engine stall speed is more than 150 rpm
below the OEM specification: indicates an engine problem.
– Over 150 rpm high = Engine stall speed is more than 150 rpm
above the OEM specification: indicates a transmission-based
problem.
– Extremely low = An extremely low stall speed, such as 30% of
the specified engine stall rpm, with no engine tattletales such as
smoking, could indicate a freewheeling torque converter stator.
– Normal but too hot = If the engine stall speed conforms to
specification but the transmission oil overheats, perform the
cool-down check. If the oil does not cool down during the 2minute cool-down check, a stuck torque converter stator could
be indicated.
Shift Point Engine
Speeds for Select Transmissions
• See Table 19-1 on page 568 of the textbook.
Adjusting Shift Points (1 of 2)
• Shift speeds can be altered by
changing the positions of the
adjusting rings.
• The adjusting ring is held in
the shift signal valve bore by a
pin that is press-fit through the
valve body housing.
• Adjustment of the valves is
performed using a valve ring
adjusting tool.
• When the ring is depressed by
the adjusting tool, the slots on
the ring that engage the pin
are released.
• The adjusting ring can then be
turned to adjust spring
pressure.
Adjusting Shift Points (2 of 2)
• Clockwise rotation increases
spring pressure.
• The slots on the adjusting ring
that engage the pin are on a
sloping ramp around the
circumference.
• This alters the spring tension
as the slots reengage the pin
in the new ring position.
• Each notch in the adjustment
ring will alter the shift point by
an incremental rpm value.
– For example, one notch might
be equal to 25, 35, 40, or 50
rpm of engine speed, based
on the particular model
transmission.
Speedometer Method
• Begin the test by checking the top speed the
vehicle can achieve in each gear before a shift
occurs.
– Some electronically managed engines may have
programming that makes these values soft.
• When the top vehicle speed has been recorded for
each gear, accelerate the vehicle at full throttle from
a standing start and note the speed at which each
upshift occurs.
• Compare the upshift rpms with the selected shift
speeds recorded in the first part of the test drive.
• The same general adjustment principles apply as in
rpm adjustment.
Test Stand Calibration
• The valve body is bolted onto
a manifold that resembles the
lower portion of the
transmission housing.
• This manifold is drilled and
tapped to mate to all the ports
and hoses required to route oil
properly through the valve
body for testing.
• The test stand can now be
used to check five principal
valve body functions:
–
–
–
–
–
Governor pressure
Modulator pressure
Hold regulator pressure
Shift points (up-down/inhibit)
Trimmer regulator operation
Shift Points without Modulated
or Adjustable Lockup
• See Table 19-2 on page 571 of the textbook.
Automatic Transmission
Troubleshooting
• See Table 19-4 on pages 572-573 in the
textbook.
Summary (1 of 4)
• Automatic transmissions should be cleaned
with a power washer to make inspection and
servicing easier. Special care should be
taken to avoid forcing water through the
transmission breather.
• Inspect the transmission for loose bolts,
loose or leaking oil lines, oil leakage, and the
condition of the control linkage and cables.
Summary (2 of 4)
• Maintaining the specified oil level in an
automatic transmission is important, as either
low or high oil levels can cause aeration of
the transmission fluid.
• At each oil change, examine the oil that is
drained for evidence of dirt or water.
• Metal particles in the oil or on the magnetic
drain plug (except for the minute particles
normally trapped in the oil filter) indicate that
damage has occurred in the transmission.
Summary (3 of 4)
• If engine coolant leaks into the transmission
oil system, immediate action should be taken
to prevent serious damage. Antifreeze
destroys the clutch materials used in
automatic transmissions.
• There are three methods of testing shift
points in automatic transmissions. Adjusting
shift points is part of routine preventive
maintenance.
Summary (4 of 4)
• Truck technicians should be able to
undertake first-level troubleshooting of Allison
transmissions using diagnostic charts.
• During initial troubleshooting, the engine and
transmission should be regarded with equal
attention, as engine problems can often be
misinterpreted as transmission problems, and
vice versa.