Transmission General Information 7D1

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 powertrain control module (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 rations with the planetary gear sets.

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

The general arrangement of the mechanical, hydraulic and internal electrical 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 4L60-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. For further information on the PCM, refer to Powertrain Control Module Description.

The programming in the powertrain control module (PCM) for GEN III V8 allows for different shift patterns, which are driver controllable through the use of the Power button. The Power button is located in the center console.

Note: All VZ Coupes do not have a Power button. The transmission fitted to these vehicles has its own specific calibration which cannot be controlled by the driver.

The calibration for this mode is for maximum comfort, with minimal intrusion of engine noise and smooth shifts under all driving conditions. When additional power is required for acceleration, full throttle upshifts are similar to those calibrated for the Power Mode.

When activated, the PCM modifies the transmission calibration in the following ways:

1. When the throttle is less than 80% open, later upshift points are provided.
2. Shift time is reduced.
3. The Torque Converter Clutch (TCC) will be applied in both the third and fourth speed ranges.

When the driver activates the cruise control (where fitted), the Power icon in the instrument clusters multi-function display (MFD) will be deactivated (provided the vehicle was operating in the Power mode) and the transmission shift pattern will switch to the cruise control pattern. When in this mode, the PCM modifies the shift pattern so that earlier downshift and later upshift points are provided.

Through the electronic programming of the logic processes contained in the PCM, the frequency of gear shifting and torque converter clutch application and release is minimized. The end result of these logic processes, is that a quick series of upshifts and downshifts (e.g. a '4-3-4' shift pattern) is minimized.

Torque management is a function of the PCM that reduces engine power under certain conditions, including transmission upshifts and downshifts.

Torque management is performed for the following reasons:

The PCM monitors the following sensors and engine parameters to calculate engine output torque:

Instances when engine power reduction is likely to be experienced, are:

The driver is unlikely to notice the torque management actions in the first two instances. The engine power output will be moderate at full throttle in the other two cases.

The PCM calculates the amount of ignition retard necessary to reduce the engine power, and cuts off spark to certain cylinders. For example the PCM disables the fuel injectors and retards spark for cylinders 1, 4, 6, and 7 in the case of a series of abusive manoeuvres.

Should 1st gear be selected and left in that range, the PCM will protect the engine from an over-speeding condition by upshifting to 2nd speed at a pre-determined point. Similarly, the PCM provides high speed, downshift protection by preventing a manual shift into 1st gear above pre-determined engine speeds.

Under severe operating conditions such as towing in high ambient temperatures, fluid temperatures can rise to a point where lubrication breakdown can occur. Vehicles, in addition to having an oil cooler fitted, the 4L65E transmission is also fitted with a transmission fluid temperature sensor located in the Transmission Range (TR) Pressure Switch Assembly (PSA).

When fluid temperatures in excess of 135°C are sensed, the torque converter clutch is applied as programmed, in 3rd or 4th gear. This action reduces further fluid temperature that occur during normal operation of the torque converter. While these high fluid temperatures are sensed, torque converter clutch apply is not available however, when the throttle opening is above 50%.

Similarly, when the fluid temperature is below 29°C, the PCM prevents torque converter clutch apply.

Should a condition occur that prevents electronic control of the transmission's functions, a 'Fail Safe' mode will default the transmission to 3rd gear when either Drive 'D' or '3' is selected, and also apply maximum line pressure. While in this mode, the vehicle operator can still manually select '2', '1', Reverse, Park or Neutral, should the need arise.