Transmission bands, which are thin steel (metal) bands with roughened inner surfaces, are anchored to the transmission case, which is the main structural skeleton of a standard transmission. By enabling transmission gear selection and action, transmission bands are a critical component of a vehicle's transmission. Transmission bands are anchored into place by small rivet-type structures called transmission anchors, or simply anchors. These anchors prevent the transmission bands from moving out of place, a condition that would seriously impede transmission operation.
Hydraulic transmission fluid, which provides the fluid force necessary to operate virtually every aspect of a vehicle transmission, provides the fluid force that results in transmission band activation. Transmission bands are connected to small fluid coupling devices called servos, which are similar in design to small plunger-operated valves. These servo mechanisms fill with hydraulic transmission fluid in response to transmission torque converter pressure, a process that results in the servo mechanisms exerting increased force against the transmission bands, which results in the bands being locked into place around the transmission drums.
A transmission band is considered a reaction device, in the same family as multiple clutch discs and one way overrunning clutches. There is a difference. A brake band is strictly a stopping and holding device. Clutches are used to hold and drive members of the planetary gear set.