Transmission General Description 7D3

The Hydra-Matic 4L65-E is a fully automatic, four speed, transmission. It consists primarily of a four element torque converter, two planetary gear sets, various clutches, an oil pump and a control valve body.

The four element torque converter contains a pump, a turbine, a pressure plate splined to the turbine and a stator assembly. The torque converter acts as a fluid coupling to transmit power smoothly from the engine to the transmission. It also hydraulically provides additional torque multiplication when required. The pressure plate, when applied, provides a mechanical 'direct drive' coupling of the engine to the transmission.

The two planetary gear sets provide the four forward gear ratios and reverse. Changing of the gear ratios is fully automatic and is accomplished through the use of various electronic sensors that provide input signals to the PCM. The PCM interprets these signals to send current to the various solenoids inside the transmission.

By using electronics, the PCM controls shift points, shift feel and torque converter clutch apply and release, to provide proper gear ranges for maximum fuel economy and vehicle performance.

Five multiple-disc clutches, one roller clutch, a sprag clutch and a brake band provide the friction elements required to obtain the various ratios with the planetary gear sets.

A hydraulic system (including the control valve body), pressurised by a vane type pump, provides the working pressure needed to operate the friction elements and automatic controls.

The general arrangement of the mechanical and hydraulic components is shown in the General Motors Powertrain Group Electronically Controlled Automatic Transmission Technician's Guide.

With traditional, hydraulically controlled transmissions, the gear shifts are controlled by the opposing pressures of hydraulic fluid in a complex system of spring-loaded valves. In this electronically controlled Hydra-Matic 4L65-E transmission, gear shift points and shift feel are determined by electrical signals sent from the PCM.

The PCM processes data every 25 milliseconds from various sensors, such as throttle position, vehicle speed, gear range, temperature, engine load and other inputs. Using this data, a signal is transmitted to the valve body shift solenoids, which activate the shift valves for precise shift control. Shift points are therefore precisely controlled and are identical from vehicle to vehicle.

Shift feel is also electronically controlled by the PCM, by signals sent to the Variable Force Solenoid, which controls fluid line pressure and it is this pressure that precisely determines how the shifts will feel. In this way, the PCM electronically synchronizes the engine and transmission into a single, integrated powertrain system, for optimum performance, shift timing, fuel efficiency and emission control.