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Technical
Service Bulletin 98-2
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Transmission Fluid Evacuation Service
There
has been a recent trend toward use of fluid evacuation systems in the
automatic transmission service industry in lieu of traditional transmission
service methods. These systems are used to pump the old fluid out of the
transmission and to refill with fresh fluid. This avoids dropping the
pan and draining the unit which can be time consuming and messy. The use
of this method to replace the transmission fluid is a clean, efficient,
and safe way to remove hot oil from a transmission. The problem, however,
is that often times it is mistakenly thought that this represents complete
transmission service and that removal, and cleaning of the pan and inspection
and servicing of the filter are unnecessary.
Some
people believe that all transmission filters are back flushed clean every
time the vehicle is turned off. This is a major misconception. Three-quarters
of all transmission filters today are not a simple screen, they are made
of felt. A felt filter CANNOT be back flushed. Felt holds dirt particles
within tiny pores in the felt. It will not wash out or flush out. If a
felt filter becomes clogged it must be replaced. Clogged filters restrict
fluid flow, which lowers pressure to clutches and bands. This can cause
slippage and eventual burnout of the transmission.
Service
manuals and textbooks on transmission service recommend that a transmission
filter be inspected and replaced, if necessary, as often as every 15,000
miles (24,140km), for severe service such as city driving, desert (hot
dusty) driving, extreme cold, frequent short trips, trailer towing, and
delivery service. In normal operating conditions the manuals recommend
to inspect and replace the filter at least every 30,000 miles (48,280km).
Even the newer vehicles with 100,000 mile (160,934km) drive train service
warranties, the manufacturer recommends filter replacement if the vehicle
sees severe service conditions.
There
have been an increasing number of instances surfacing recently regarding
transmission failures shortly after an evacuation service, without filter
removal. At the time of a fluid evacuation service, there is no way to
know the condition of the filter and how clogged it may be. The filters
job is to collect and hold contaminants, (dirt, metal filings, friction
particles, etc.), and prevent these particles from causing malfunction
in such components as electronic force motors and solenoids. Today's transmissions
are far more susceptible to malfunctions caused by fine dirt contamination.
Without servicing the filter, there is no way to know if the filter is
clean of debris or nearing capacity. If the filter is nearing capacity,
transmission failure may not be far off. This is also a sign that there
may be other internal problems in the transmission. Recognizing these
warning signs could eliminate major service later.
Most
of the transmission failures after an evacuation service have occurred
primarily on relatively high mileage transmissions that have not been
serviced in some time. One reason for this is that the sludge and dirt
buildup within the transmission will not completely be removed during
the service. When the new fluid (which has detergent properties) is placed
in the transmission, over days and weeks, the internal components begin
to wash the insides of the transmission.
This
sludge does finally work loose and settles in the transmission filter,
clogging it up even further than it may have been before service. In these
extreme cases, where service has not been performed in some time, changing
the filter may not completely fix the problem. Some mechanics recommend
a second service a few weeks after the first, replacing the filter again,
which may be partially clogged due to the cleaning process in the transmission.
Even
if the fluid evacuation method is desired to remove the used transmission
fluid, the pan should be removed also, and an inspection should be made
of the pan contents, fluid, and filter to determine the condition of the
transmission. Aluminum filings in the pan or iron filings on the pan magnet
are signs of internal wear and may give light to potential problems in
the transmission. Transmission service is performed for preventative maintenance.
Evaluating the overall condition of the transmission by removing the pan
should be part of this preventative maintenance also.
The
Filter Manufacturers Council urges everyone to dispose of all used filters
properly.
For additional information, contact:
Filter Manufacturers
Council
P.O. Box 13966
Research Triangle Park, NC 27709-3966
Phone: 919/406-8817 Fax: 919/406-1306
www.filtercouncil.org
Administered by Motor & Equipment
Manufacturers Association
Created June 1998
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