4R70W (AODE-W)

DESCRIPTION
This transmission has wide ratio gears and is a four speed rear wheel drive automatic with an electronic shift, torque converter clutch control, and line pressure controls. This transmission uses a double pinion compound gear set to produce four forward speeds and reverse. Two bands, two one-way roller clutches, and four friction clutches are used to hold or drive various planetary gear set members.

OPERATION
With selector lever in 1 position, the transmission will start and remain in first gear until the selector lever is moved to another position. In 3 position, the transmission will automatically shift through 1-2-3 range, but will not engage overdrive. In D position, the transmission will automatically select the appropriate time to shift into overdrive (4th gear). The design of the transmission features a split torque path in third gear, where 40 percent of the engine torque is transmitted hydraulically through the torque converter and 60 percent is transmitted mechanically through solid connections (direct drive input shaft) to the driveshaft. When transmission is in overdrive (4th gear), 100 percent of engine torque is transmitted through the direct drive input shaft.

CONSTRUCTION

Cross-sectional View Of Automatic Overdrive Transmission:

The transmission consists of a torque converter assembly, compound planetary gear train, and a hydraulic control system. For gear control the transmission has four friction clutches, two one-way roller clutches, and two bands. Overdrive is accomplished by the addition of a band to lock the reverse sun gear while driving the plan et carrier. The torque converter operation is similar to other types of automatic transmission, but has an added damper assembly and input shaft for 3rd gear and overdrive. The direct drive input shaft couples the engine directly to the direct clutch. This shaft is driven by the torque converter cover through the damper assembly which cushions engine shock to the transmission.

NOTE: For safety purposes, the transmission also incorporates a brake shift interlock system. This prevents the gear shift lever from being shifted from Park (with key in the ON position) unless the brake pedal is applied. The brake shift interlock system includes an actuator mounted at the base of the steering column that runs continuously while the ignition is in the ON position.