Automatic Transmission Fluid Filter

An automatic transmission filter's job is to remove contaminants from automatic transmission fluid (ATF) so that they do not damage the automatic transmission. Most of these filters are contained within the transmission (commonly just past the transmission pan) but can also be an external filter that appears similar to a spin-on oil filter. A few models of transmissions will use both filters.

Internal ATF Filters

A majority of automatic transmissions use their filters as the fluid pickup in the base of the transmission pan. Internal filters come in two designs, a surface filter or a depth filter.

Surface Filter

A surface filter is a mesh that is submerged in the fluid in the bottom of the transmission.

Depth Filter

Most modern automotive transmissions use a depth filter, which is a filter element contained in a shell of plastic, metal, or both. The case has an opening at the bottom so that it is sure to pull in only transmission fluid even if the pan is almost empty.

External ATF Filters

A few automatic transmissions have an external filter that can be removed without taking anything off of the transmission to access it. The Saturn S-Series cars and many Subaru models had automatic transmissions with this type of filter. The filter spins off like a typical oil filter does.

Filter Element Materials

There are many types of filter elements available, but the most common material used is paper.

Secondary Filters

Many transmissions also have a secondary filter deeper within the unit, put there as a secondary level of protection for vital fluid passageways. These filters typically do not need replacing and only get replaced during a rebuild.