An automatic transmission includes a planetary gear system with several different size gears, a hydraulic system that uses special transmission fluid sent under pressure by an oil pump through the valve body to control the clutches and the bands that control the gears; a governor and modulator or throttle cable that control when to shift; seals and gaskets to keep the oil from leaking; a torque converter that allows the vehicle to stop in gear; microprocessor-controlled electronic sensors and solenoids, including those that connect to a computer.

The most common problem with an automatic transmission has to do with the transmission fluid. If it is low, old, or burned smelling, it may cause problems that do not allow the vehicle to shift properly. A loss of transmission fluid can allow air to get into the hydraulic system causing multiple problems. A slip or jerk will usually indicate that pressure has been lost for this reason. If the vacuum hose on the modulator Transmission Headquarters is clogged or disconnected, the transmission will delay shifting or might not shift at all, and you may hear a loud whining sound which increases as the car accelerates. If the cable is broken, disconnected or misadjusted, the transmission will not shift properly. If the linkage is misaligned or disconnected multiple problems may occur. With so many components and so many possible problems, it takes experts like those here at Transmission Headquarters to properly do automatic transmission repairs.