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Transmission General Description
The Hydra-matic 8-Speed RWD is a fully automatic, 8-speed, rear-wheel drive, electronic-controlled transmission. The eight
speed ratios are generated using four simple planetary gearsets, two brake clutches, and three rotating clutches. The resultant
on-axis transmission architecture utilizes a squashed torque converter, an off-axis pump and four close coupled gearsets. The
three rotating clutches have been located forward of the gearsets to minimize the length of oil feeds which provides for enhanced
shift response. There are different variants of the transmission, all based on torque capacity. Architecture is common between the
variants, and component differences are primarily related to size.
The transmission architecture features a case with integral bell housing for enhanced powertrain stiffness. A unique pump drive
design allows for off-axis packaging very low in the transmission. The pump is a binary vane type which effectively allows for
two pumps in the packaging size of one. This design and packaging strategy not only enables low parasitic losses and optimum
priming capability but also provides for ideal oil routing to the controls system, with the pump located in the valve body itself. The
transmission control module (TCM) is externally mounted, enabling packaging and powertrain integration flexibility. The controller
makes use of three speed sensors which provide for enhanced shift response and accuracy.
The 4-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 smoothly transmit power 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 planetary gear sets provide the 8 forward gear ratios and reverse. Changing gear ratios is fully automatic and is accomplished
through the use of a transmission control module (TCM). The TCM receives and monitors various electronic sensor inputs and
uses this information to shift the transmission at the optimum time.
The hydraulic system primarily consists of an off-axis chain-driven binary vane-type pump located in the valve body, and 2 control
valve body assemblies. The pump maintains the working pressures needed to stroke the clutch pistons that apply or release
the friction components. These friction components, when applied or released, support the automatic shifting qualities of the
transmission.
The friction components used in this transmission consist of 5 multiple disc clutches. The multiple disc clutches deliver 7 different
gear ratios, 8 forward and one reverse, through the gear sets. The gear sets then transfer torque through the output shaft.
The transmission may be operated in any of the following gear ranges:
PARK (P)
This position locks the rear wheels and prevents the vehicle from rolling either forward or backward. PARK is the best position
to use when starting the vehicle. Because the transmission utilizes a shift lock control system, it is necessary to fully depress
the brake pedal before shifting out of PARK. For safety reasons, use the parking brake in addition to the PARK position.
REVERSE (R)
This position allows the vehicle to be operated in a rearward direction.
NEUTRAL (N)
This position allows the engine to be started and operated while driving the vehicle. If necessary, you may select this position in
order to restart the engine with the vehicle moving. This position should also be used when towing the vehicle.
DRIVE (D)
Drive range should be used for all normal driving conditions for maximum efficiency and fuel economy. Drive range allows the
transmission to operate in each of the 8 forward gear ratios. Downshifts to a lower gear, or higher gear ratio, are available for
safe passing by depressing the accelerator or by manually selecting a lower gear in the manual mode range.
MANUAL (M) SPORT MODE (S)
This position allows the driver to utilize the Driver Shift Control (DSC) system, or manual mode. When the shift selector lever
is moved to the M/S position, the driver may select upshifts or downshifts by using the paddle switches located on the steering
wheel. An upshift is requested by pushing either + button forward. A downshift is requested by pulling either + button rearward
toward the driver.
To protect the engine or transmission from damage, the TCM will only allow you to shift into a gear appropriate for engine
speed and vehicle speed.
Supermatic Transmission Controller Kit
TITLE
19371499
IR
AP1
PART NO.
6
30
SHEET
OF
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