The speedometer drive assembly is geared to the output shaft. A flexible drive cable connects the drive assembly to the speedometer in the instrument panel. Transmissions without a speedometer drive have a wiring harness connected to a vehicle speed sensor, also located at the output shaft.

At the rear of some transmission housings is a round metal canister with a tubular opening; this is the vacuum modulator.

A vacuum line from the engine's intake manifold is connected to the opening. This supplies vacuum to operate the modulator. The vacuum modulator is a load-sensing device that increases or decreases fluid pressure in response to the vacuum signal. Transmissions not equipped with a vacuum modulator use a throttle cable or electronics to sense engine load and change fluid pressures. Increasing the fluid pressure holds the planetary control units tightly to reduce the chance of slipping while under heavy load.

Linkages

The throttle cable is connected to a lever located at the left front of the transmission housing. The throttle lever is moved by the throttle linkage at the carburetor or throttle body of the fuel injection system. The throttle lever moves according to the position of the throttle pedal. Some automatic transmissions use a rod-type linkage assembly, not a cable, to move the throttle lever. The other lever is the manual shift lever. As the gear shift selector is moved into its various positions, the manual lever moves the manual shift valve in the transmission's valve body. The movement of the gear selector is directed to the manual shift lever via a cable or shift rod assembly. Each gear position of the lever and/or shift valve is held in place by the internal linkage seating itself into the various seats or detents for the gear range selected.

Cooler Lines

The housings are also fitted with an ATF cooler outlet. ATF leaves the torque converter and is directed to the transmission cooler in the vehicle's radiator. Some vehicles have an auxiliary cooler separate from the radiator. The cooler return line sends the cooled fluid back to the transmission housing.

Most transmissions are also equipped with plugs that can be removed to connect hydraulic pressure gauges for testing the operation of the transmission.

Electrical Connections

Many different electrical switches, sensors, and connectors may be connected to the housing. As more electronics are used to control and monitor the functioning of the transmission, more connectors and electrical devices will be found at the housing. One of the more basic switches that may be found is the neutral safety switch, which allows the engine to start only when the transmission is in neutral or park. The backup light switch is sometimes incorporated with the neutral safety switch, as are other shift position switches. These switches may be individual switch assemblies. Connectors for shift solenoids may also be present on the outside of the case.

Mounts

The weight of the transmission or transaxle is supported by the engine and its mounts and by a transmission mount. These mounts are not only critical for proper operation of the transmission, but they also isolate transmission noise and vibrations from the passenger compartment. The mountings for the engine and transmission keep the power train in proper alignment with the rest of the drive train and help to maintain proper adjustment of the various linkages attached to the housing.