Fluid evacuation systems in the automatic transmission service industry are commonly being used in lieu of traditional transmission service methods. The use of this method to replace the transmission fluid is a clean, efficient and safe way to remove hot oil from a transmission. However, there are some risks to doing a fluid evacuation service.
There have been instances 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. Today’s transmissions are far more susceptible to malfunctions caused by fine dirt contamination. The filter’s job is to collect and hold contaminants and prevent these particles from causing malfunction in such components as electronic force motors and solenoids. 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.
Some of the transmission failures following evacuation service have occurred on relatively high-mileage transmissions that have not been serviced in some time. One reason 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 technicians 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.
Fluid evacuation service should not be mistaken for complete transmission service. Some people believe that the removal and cleaning of the pan and inspection and servicing of the filter are unnecessary, but this is a major misconception. Most transmission filters contain felt media. Felt holds dirt particles within tiny pores that 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.
Typically transmission service is performed at 15,000 miles 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 it is recommended to inspect and replace the filter at least every 30,000 miles. Even in vehicles with 100,000-mile or higher drivetrain service warranties, the manufacturer recommends filter replacement sooner if the vehicle sees severe service conditions. Refer to your manufacturer’s recommendations for your particular application.
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 preventive maintenance. Evaluating the overall condition of the transmission by removing the pan should be part of this preventive maintenance also.
Courtesy of the Filter Manufacturers Council