Mercedes 722.

9 Preliminary Information, Part 1

Mercedes 722.9
Preliminary
Information, Part 1 by Mike Souza

T he Mercedes 722.9
transmission has been
around since the later
part of 2004, but there still
isn’t a lot written about it. The
722.9 can be found in these
Mercedes vehicles:
2004-06 – SL500

2005-up – CL500, E500,

S430, 500, SLK350,
55 AMG

2006-up – C230, 280, 350,

CLK350, CLS500, E350,
E63 AMG, R350, 500,
SLK280 • Earlier upshifts and later
downshifts
2007-up – CLK550, CLS550, • 37-47 MPH • Reverse gear 2 (2.231:1)
CL600, CLS63 AMG, E550, acceleration times are short-
E63 AMG, GL320, 450, ened by 23-28% (model The transmission will start in first
ML350, 500, ML63 AMG, dependant). gear if any of these conditions apply:
R63, and S550 • Fuel consumption is reduced • 1st gear is selected manually.
by up to 4%. • ¾-throttle to full-throttle
That’s a lot of vehicles! This 5th • Noise levels are reduced due acceleration from start.
generation transmission is the first 7- to lower engine speed in 5th, • Cold engine temperature (pre-
speed automatic produced by Mercedes 6th and 7th gear at constant catalytic warmup).
Benz. The Mercedes designation for vehicle speed.
this transmission is New Automatic • Flexible adaptation to vehicle Emergency Function
Gearbox 2 (NAG2) or 7G–Tronic. and engine. or Limp-Home Mode
Along with seven forward speeds this There are a variety of failsafe
unit also has two reverse gears ratios Variable Shift modes:
(similar to the 722.6) depending on Programming • If a solenoid doesn’t work the
whether it’s in Sport or Comfort mode. There are two basic shift programs affected gear is blocked. For
that can be varied by the customer example: if solenoid Y3/8y7
Shift Strategy (similar to the 722.6) using the S or C or the B3 clutch is defective,
Shift strategy improvements button on the Electronic Shifter Module you won’t have 1st, 7th or
include: (ESM): reverse in S mode.
• Computer reaction time is 0.1 1. S (Sport) • If a hydraulic fault prevents a
second shorter. • 1st gear starts gear from engaging, the previ-
• Downshifts are shortened by • Normal shift points ous gear will remain applied.
up to 0.2 seconds. • Reverse gear 1 (3.416:1) • If the computer defaults to
• Coasting downshifts are short- 2. C (Comfort) limp mode while driving,
ened by 0.4/2.5 seconds. • 2nd gear starts it’ll turn all solenoids off.

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 Figure 1
Solenoids that are normally transmission will be in 6th redirected to the B2/BR sole-
open will allow full pressure gear. After shifting to park, oil noid by emergency operation
to selected clutches and the pressure from K2 solenoid is valves, and the transmission

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 Mercedes 722.9 Preliminary Information, Part 1

Figure 2 Figure 3

Figure 4
will now provide reverse, and • B1 Brake Clutch Solenoid • Oil Control Float 2 (32)
2nd gear with the selector in (Y3/8y5) (normally open)
drive (figure 1). • B2 Brake Clutch Solenoid Fluid Level Float Function 2
(Y3/8y6) (normally closed) The extended length of the trans-
Electronic Control • B3 Brake Clutch Solenoid mission (41mm) allows oil to slosh
Components (Y3/8y7) (normally closed) forward during hard stops. To prevent
Here’s a diagram of the compo- • Torque Converter Lockup oil foaming from gears running in fluid,
nents that make up the electronic con- Solenoid (Y3/8y8) (normally Mercedes added a front float.
trol system (figure 2). closed)
• Transmission Control Module Three Speed Sensors
(Y3/8n4) (flash capable) Normally Closed: high current, high These components are built into
• Working Pressure Control pressure; no current, no pressure. the valve body assembly (figure 3):
Solenoid (Y3/8y1) (line/nor- Normally Open: no current, high pres- • Turbine RPM Sensor (Y3/8n1)
mally open) sure; high current, low pressure. (Front)
Normally open solenoids are used
• K1 Clutch Solenoid (Y3/8y2) • Internal RPM Sensor (Y3/8n2)
for limp mode with no current to the
(normally closed) (Center)
transmission.
• K2 Clutch Solenoid (Y3/8y3) • Output RPM Sensor (Y3/8n3)
(normally open) (Rear / Hall Effect)
• K3 Clutch Solenoid (Y3/8y4) Two Oil Floats • Selection Range Sensor
(normally open) • Oil Control Float 1 (31) (Y3/8s1)

32 GEARS March 2009

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 Mercedes 722.9 Preliminary Information, Part 1

Unlike the Lepelletier

geartrain, the 722.9
geartrain has the
sun gear fixed to the
K1 clutch assembly,
located in the front of
the unit (figure 6).
three clutch packs to provide seven
forward gear ranges and two reverse
ranges.
• 4 Multi-Disc Brakes
• 3 Multi-Disc Clutches
• No Sprag

Gear ratios are achieved with one

Ravigneaux and two simple planetary
assemblies shown in figure 5. Unlike
the Lepelletier geartrain, the 722.9
geartrain has the sun gear fixed to the
K1 clutch assembly, located in the front
of the unit (figure 6). The Ravigneaux
planetary assembly is also located in the
front section of the transmission (figure
7). There are two simple planets located
toward the back of the transmission,
one in front of the other (figure 8).

Fluid Type
The 722.9 uses a newly-developed,
suggested-use-only transmission fluid,
referred to as ATF 3353 (figure 9). It
Figure 5 promises a higher friction consistency,
thermal stability, and temperature rat-
Range Sensor Function / small ring gear). ing. ATF 3353 can also be used on
2. The center speed sensor (Y3/8n2) previous model 722.3/.4/.5/.6 transmis-
The Y3/8s1 range sensor is monitors the Ravigneaux carrier sions. This special ATF is available
built into the ECM ribbon cable, and speed (ring gear of rear planet). from Shell & Fuchs Europe oil sup-
can’t be replaced individually. It’s a 3. The rear speed sensor (Y3/8n3) pliers in 1 liter bottles under Mercedes
Permanent Magnetic Linear Contactless monitors the park pawl gear (excit- Benz part number A001 989 45 03 10.
Displacement (PLCD) sensor; it has a er ring/2 Hall Effect). No scheduled maintenance is
permanent magnet mounted to the man- required for the 722.9 (fill for life).
ual valve, which changes the magnetic The magnets for these sensors are In the next issue we’ll go into
field and output voltage as you move molded in a plastic ring and secured sequential shifting, powerflow, and
the selector. If the sensor signal doesn’t inside nonferrous flanges. some unusual features associated with
register properly with the computer, the Mercedes 722.9.
it’ll put the system into limp mode. Transmission Fluid
Temperature
Speed Sensor Function The transmission fluid temperature
The 722.9 uses three speed sen- sensor is built into the TCM, and isn’t
sors to monitor transmission operation replaceable separately.
(figure 4):
1. The front speed sensor (Y3/8n1) Clutch Components
monitors turbine speed (input shaft The 722.9 uses four brakes and

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 K1 Clutch
Assembly

Figure 6

Ravigneaux
Planetary Gears

Figure 7

Planetary
Assembly

Figure 8 Figure 9

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