Automatic transmissions have internal filters designed to capture only large particles. These filters are designed as a pickup to keep large particles from flowing through the transmission. These filters are on the suction side of the pump. The 4r100/e4od and many other transmissions were never equipped with this type of external filter. The allison in the chevy and many medium duty and heavy duty trucks come equipped from the factory with an external transmission filter. This is not a new idea in transmission maintenance and protection. The oem filter location requires that you pull the pan to change or check the filter. With our kit you can simply spin on a new filter element. With the optional pressure gauge to monitor when you should change your filter, you can avoid unnecessary filter changes. Filter is on the "push" side of the pump. This location allows for a filter with increased efficiency -- or smaller micron rating. Normally, you have the dirty fluid in the pan. The oem filter hopefully catches the really big particles before it enters the valves and pump. After running through the transmission, it leaves as "dirty" fluid. This fluid will have clutch dust and other impurities which are all normal in any automatic transmission. This dirty fluid would be re circulated back to the pan. With our kit you can catch dirty fluid before it makes back to the pan. Keeping the fluid clean, keeps your valve body clean and keeps your transmission shift quality at its highest. After installation of our external kit the filter in the pan now acts simply as a pickup for the pump and virtually never needs changed.