How Does Transmission Fluid Work?

by Jason Medina

Transmission Fluid Supplies Hydraulic Pressure

Transmission fluid works by supplying an automatic transmission with the hydraulic pressure necessary to function. Unlike a manual transmission, which uses gears, levers, and linkages operated manually to shift gears and engage and disengage the transmission, an automatic transmission uses automatic transmission fluid to perform vital transmission functions. As automatic transmission fluid flows throughout an automatic transmission, it flows under varying levels of pressure, levels that are determined by engine load, driving conditions and various gear selections.

Torque Converter Pressurizes Transmission Fluid

Without the action of the transmission torque converter, which is a cylindrical-shaped pump located at the front of an automatic transmission, transmission fluid would be virtually useless. Transmission fluid must be pressurized for it to perform properly. The transmission torque converter, which is filled with small fans, metal fins, and a small internal pump and spinning rotor, sucks transmission fluid into its inner housing and rapidly spins and propels the transmission fluid about its inner housing. As the transmission fluid spins, it gains speed and develops a tremendous fluid pressure force. After being sufficiently pressurized, the transmission fluid flows out of the torque converter and into the main functional part of a vehicle's transmission, the part that houses the transmission gears, bands and linkages.

Flowing Transmission Fluid Lubricates and Cools

In addition to supplying the fluid force necessary for a transmission to shift, transmission fluid also serves to lubricate and cool the inner workings of a transmission. Shifting gears, engaging and disengaging the transmission, rotating transmission bands and linkages--all of these actions produce heat and require constant lubrication. Without circulating transmission fluid, a transmission would quickly deteriorate. Circulating transmission fluid flows along a series of small channels and ports within a transmission, small openings that allow it to lubricate and cool all of the critical parts within the transmission.