System description of automatic transmission - 8HP65AX

Table of contents
System overview
System function
System components
Instructions for the workshop

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System overview

Overview of automatic transmission installation position

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Automatic transmission
Automatic selector lever

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4

Transmission parking lock emergency
release
Control unit for rear axle transmission

The 8HP65AX 8-gear automatic transmission was developed for vehicles with
longitudinal engines and all-wheel drive. The main automatic transmission of the
8HP65AX is a further development of the Audi AL552 (8HP65A) transmission. The rear
axle transmission and cardan shaft are further developments of the corresponding
components from the Cayenne E2. The Hang-On transfer case is a further development
of the component used in the Macan. The manufacturer of the automatic transmission is
ZF-Getriebe GmbH in Friedrichshafen.
In contrast to its predecessor AL552, the 8HP65AX from Porsche has a Hang-On
transfer case for four-wheel drive, which is supplied by Magna. The new gear wheel set
concept, consisting of four planetary gear sets with five shifting elements, minimises
drag losses and increases transmission efficiency.
The basic transmission is also fully hybrid-capable. The modular system developed by
ZF Friedrichshafen AG makes it possible for micro and full hybrid systems to be
equipped with the basic transmission of the automatic transmission.

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System function

Cutaway view of clutch

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Circlip
Multi-disc brakes
Ondular washers

Clutch
The wet multi-disc clutch is actuated using a ball ramp system and an electric actuator
with integrated control unit.
The drive and front axle output use two coaxial shafts: drive outside and front axle
output drive inside. The clutch is operated in continuous slip and has a capacity of 1200
Nm ±10% in continuous operation. Short-term peak torques of 1400 Nm are possible,
with a maximum of 100 instances over the entire service life. The direction of rotation of
the rear axle output drive is clockwise when viewed in the direction of travel.

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System function
Switching elements
The 8-speed 8HP65AX automatic transmission consists of 5 switching elements in the
form of 3 revolving clutches (C, D and E) and 2 fixed brakes (A and B).
Due to the arrangement of the planetary gear sets, two switching elements are always
open and three are always closed for each gear (see table): clutch logic).
Brakes A and B are fitted with ondular washers between the vanes. When open, they
allow the clearance necessary to reduce the drag torque as much as possible. This
reduces fuel consumption by about 1.5% while also reducing CO 2 emissions. Since the
switching elements have no freewheel and only one clutch changes, gear shifts are
always carried out without interrupting the flow.

Clutch logic

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System function

Torque flow in rear axle output drive

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Input shaft and output to rear axle (input torque)
Output to front axle
Multi-plate clutch (output torque of front axle drive)
Ball ramp
Transmission of input torque to rear axle

Transfer case (Hang-On)
The flange-mounted Hang-On transfer case with bolted damper and heat shield is
required for all-wheel drive. It is supplied by a separate oil supply. Porsche has also
given the new transmission housing a modified flange contour for the converter bell.
There is also a reinforced differential cover and further changes to the interior. Among
other things, ventilation tubes, bore holes and bearings were revised. The former
hydraulic oil reservoir has been replaced by an electric control unit which, together with
the actuator, controls the multi-disc clutch.
When the multi-plate clutch is open, the input torque is transmitted directly to the rear
axle. Closing the clutch controls the percentage distribution of the input torque to the
front and rear axles. The input torque is transmitted back to the transmission via the
internal shaft and from there to the front axle final drive via the output unit and the side
shaft.

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© Copyright by Dr. Ing. h.c. F. Porsche AG

System function
Three-line converter
The new three-line converter built into the 8HP65AX 8-speed automatic transmission is
an optimised hydrodynamic torque converter. The converter lockup clutch is supplied
through third control line (at 5-6 bar operating pressure). The first and second lines are
used for oil supply and return.
The torque converter is equipped with a slip-controlled converter lockup clutch. By using
a turbine torsional damper and a speed adaptive damper with centrifugal pendulum,
torsional vibrations between the engine and transmission are decoupled, providing
greater shifting comfort.

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© Copyright by Dr. Ing. h.c. F. Porsche AG

System components

Component overview of automatic transmission

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Front-axle final drive (VAG integrated)
Automatic transmission (main transmission)
Transfer gear with Hang-on
Cardan shaft (inserted in front, bolted in rear)
Rear axle differential
Transmission parking lock operating cable
Transmission parking lock emergency release

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© Copyright by Dr. Ing. h.c. F. Porsche AG

System components

Vane pump
The new mechanical hydraulic pump from manufacturer Ixetic GmbH, used in the
transfer case of the 8HP65AX 8-speed automatic transmission, has been given a more
efficient housing with an oval design for the delivery chamber. This means that the vane
pump conveys twice on each turn. The pump is operated with a timing chain from the
central drive shaft.
Advantages of the new vane pump:
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•
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Lighter and smaller than before
The drivers can no longer be damaged
Driving by timing chain

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System components
Mechatronics
The hydraulic control unit and the electronic transmission control unit are integrated into
a single unit: the mechatronics. This is installed in the transmission earn the ATF pan.
The following components are integrated into the mechatronics:
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•
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Transmission control unit
Solenoid valve
Yellow pressure control valves: rising characteristic from 0 to 4.7 bar
Blue pressure control valves: falling characteristic from 4.7 to 0 bar
Magnet for transmission parking lock
Transmission input speed sensor
Transmission output speed sensor
Temperature sensor for control unit
Sensor for transmission parking lock

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System components

Selector lever for automatic transmission (basic)
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Unlocking button
Selector lever
Drive mode display

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5

P-button (transmission parking lock)
Electric parking brake

Thanks to complete shift-by-wire technology, there is no longer any mechanical
connection between the selector lever and the transmission. This enables short shifting
paths in the automatic gear-selection gate and reduces shifting forces. The comfortable
operation is thus purely registration of driver requests, with no mechanical fallback level.
Transmission ranges D, R and M are available for selection.
In order to use the Triptronic S function on the steering wheel, manual mode M must be
used. The release button on the selector lever prevents unwanted switching operations.
It must be pressed in order to be able to move the gear lever in the automatic gearselection gate. The selector lever returns to the middle starting position after each
operation. You can only switch to operating mode M from operating mode D. The
transmission reaches top speed in sixth gear. The seventh and eighth gears are used
for the most efficient driving style possible, increasing long-distance comfort. The low
engine speed further reduces interior noise levels and fuel consumption.
Start/stop operation
The Auto-Start/Stop function has also been refined further, and now switches the
engine off when approaching a traffic light. This increases comfort and reduces fuel
consumption. While the Audi AL552 transmission still has a pressure accumulator, the
Porsche 8HP65AX transmission has an electric auxiliary pump for the oil pressure,
which regulates the oil supply during start/stop operation if required.
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System components

Parking-lock gear
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Parking-lock gear
Driving dog

Transmission parking lock
The transmission parking lock is actuated electrohydraulically and is operated via the
P-button on the selector lever. When the ignition is switched off or the vehicle is left in
the operating modes D, M or R, the transmission parking lock is engaged automatically.
The vehicle can also be moved with the driver's door open and the driver's seat belt
unfastened if the electric parking brake is released and the D, M or R operating mode is
selected. In this case, the transmission parking lock is not activated automatically. An
emergency release of the transmission parking lock is also possible when it is activated.

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System components
Emergency release of the transmission parking lock
The emergency release is located in the driver's footwell. Using a socket wrench
located in the on-board tool kit, the transmission parking lock can be permanently
unlocked using an operating cable. This should only be done in the following situations:
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When the vehicle has to be towed
If the transmission parking lock cannot be unlocked electrohydraulically due to a
malfunction
If the vehicle must be manoeuvred or moved but the on-board voltage is
insufficient
If the engine is not running and the vehicle must be manoeuvred or moved in the
workshop, for example

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Instructions for the workshop

Transmission identification
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Position of identification on vehicles with 4-cylinder and 6-cylinder engines (arrow = reading
direction)
Position of identification on vehicles with 8-cylinder engines (arrow = reading direction)
Transmission no.
Parts list no.
Electric motor no.
Customer and type name code

The transmission identification 8HP65AX is made up as follows:
8HP65 AX PH -

Gears
Hydrodynamic starting element
Planetary transmission
Type designation
Variant (X for all-wheel drive)
Hybrid (for hybrid vehicles only)

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Instructions for the workshop

Overview of transmission parking lock
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Emergency release mechanism (driver's
side footwell)
Operating cable A
Rapid-action coupling

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Operating cable B
Selector lever for emergency release
Mushroom seat

Emergency releasing the transmission parking lock
Important: Before activating the emergency release of the transmission parking lock, the
vehicle must be secured against rolling away, for example by activating the electric
parking brake or depressing the brake pedal.
Note:
There must be some oil pressure to unlock the transmission parking lock.
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Remove the cover in the footwell on the driver's side.
Insert the emergency release socket wrench into the actuating mechanism.
Push the socket wrench down and turn it clockwise 90 degrees until it clicks into
place.
Leave the socket wrench inserted.

As soon as the emergency release of the transmission parking lock is actuated,
operating mode N is displayed in the instrument cluster.

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Instructions for the workshop
Locking the transmission parking lock again
Note:
To remove and lock the transmission parking lock, do not turn the socket wrench back,
as this may damage the transmission.
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Pull the socket wrench vertically up and out.
Fit cover.

Reduction of structure-borne noise transmission
A special feature is the positioning of the emergency release operating cable to the gear
shift lever. The end of the operating cable is equipped with a rigid rod and a mushroomshaped seat which grips around the gear shift lever without contacting it. This largely
prevents transmission of structure-borne noise from the transmission to the operating
cable and thus its transmission into the vehicle interior. The seat and gear shift lever
only come into contact when the emergency release is actuated.

Porsche Cayenne
© Copyright by Dr. Ing. h.c. F. Porsche AG

Instructions for the workshop

Overview of separate oil supply systems

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Transfer case breather hose
Ventilation bore
Plastic ATF pan with integrated suction
filter

A
B
C

Oil system 1: Hang-On
Oil system 2: Basic manual transmission
Oil system 3: FA differential and output
drive unit

Separate oil supply systems
The 8HP8565 has three separate oil supply systems (A, B and C), eliminating the need
for a secondary pump in the transfer case.

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Instructions for the workshop

Overview of oil drain plugs

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ATF drive plug (bayonet lock)
Oil drain plug on intermediate housing
Oil drain plug on transfer gear
Oil drain plug on transfer gear
Oil drain plug on intermediate housing
ATF oil filler screw
Oil filler screw on front final drive
Oil drain plug on front final drive

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Instructions for the workshop
Removing the transmission
In general, it must be ensured that all necessary aids are available before starting work.
Turn the front wheels to straight-ahead position. Always perform work on the
transmission as described in the relevant Workshop Manual.
General instructions on working on the transmission
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When working on the transmission, there is a danger that the transmission
control unit (mechatronics) may be destroyed by static discharge.

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When the mechatronics has been removed, make sure that it is only placed with
the screw head side down to avoid damaging the sensor on the rear side. When
replacing the mechatronics, a second person is required during installation to
prevent the unit from tilting.

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Do not support the removed transmission on the ATF cooler or the ATF pan.

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To prevent damage to the transmission after installation, all plugs attached to the
ATF lines and transmission must be removed. If these are forgotten, the ATF
cooling will no longer work and the transmission will be damaged.

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When transporting and working on the transmission, it is possible that axle oil
and ATF may mix via the common transmission vent if the transmission is tilted
too much.

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The engine must not be started if there is no longer ATF in the transmission or
the mechatronics have been removed.

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The clutch must always be pre-filled to avoid possible air inclusions.

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The clutch clearance can only be adjusted during assembly by using circlips of
different thicknesses.

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To simplify transmission removal and installation, the emergency release
operating cable consists of two parts connected to one other via a quick
connector.

Porsche Cayenne
© Copyright by Dr. Ing. h.c. F. Porsche AG

Instructions for the workshop
Legal Notice
Dr. Ing. h. c. F. Porsche
Aktiengesellschaft
Postfach 1108
D-71634 Ludwigsburg
Department: After Sales Engineering/Diagnostics
Editorial work: Technical Service Diagnostics (VAT3)
12/2018
Diagrams, descriptions and schematic drawings are provided for illustrative purposes
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© Copyright by Dr. Ing. h.c. F. Porsche AG