electronically controlled 5-speed transmission with a
lock-up clutch in the torque converter. The ratios for
the gear stages are obtained by 3 planetary gear sets.
Fifth gear is designed as an overdrive with a high-
speed ratio.

NAG1 identifies a family of transmissions and

means “N”ew “A”utomatic “G”earbox, generation 1.
Various marketing names are associated with the
NAG1 family of transmissions, depending on the
transmisson variation being used in a specific vehi-
cle. Some examples of the marketing names are:
W5A300, W5A380, and W5A580. The marketing
name can be interpreted as follows:

• W = A transmission using a hydraulic torque

converter.

• 5 = 5 forward gears.

• A = Automatic Transmission.

• 580 = Maximum input torque capacity in New-

ton meters.

The gears are actuated electronically/hydraulically.

The gears are shifted by means of an appropriate
combination of three multi-disc holding clutches,
three multi-disc driving clutches, and two freewheel-
ing clutches.

Electronic transmission control enables precise

adaptation of pressures to the respective operating
conditions and to the engine output during the shift
phase which results in a significant improvement in
shift quality.

Furthermore, it offers the advantage of a flexible

adaptation to various vehicle and engines.

Basically, the automatic transmission with elec-

tronic control offers the following advantages:

• Reduces fuel consumption.

• Improved shift comfort.

• More favourable step-up through the five gears.

Fig. 1 NAG1 Automatic Transmission

1 - TORQUE CONVERTER

11 - PARKING LOCK GEAR

2 - OIL PUMP

12 - INTERMEDIATE SHAFT

3 - DRIVESHAFT

13 - FREEWHEEL F2

4 - MULTI-DISC HOLDING CLUTCH B1

14 - REAR PLANETARY GEAR SET

5 - DRIVING CLUTCH K1

15 - CENTER PLANETARY GEAR SET

6 - DRIVING CLUTCH K2

16 - ELECTROHYDRAULIC CONTROL UNIT

7 - MULTI-DISC HOLDING CLUTCH B3

17 - FRONT PLANETARY GEAR SET

8 - DRIVING CLUTCH K3

18 - FREEWHEEL F1

9 - MULTI-DISC HOLDING CLUTCH B2

19 - STATOR SHAFT

10 - OUTPUT SHAFT

20 - TORQUE CONVERTER LOCK-UP CLUTCH

AUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATION

21 - 3

• Increased service life and reliability.

• Lower maintenance costs.

TRANSMISSION IDENTIFICATION

The transmission can be generically identified

visually by the presence of a round 13-way connector
located near the front corner of the transmission oil
pan, on the right side. Specific transmission informa-
tion can be found stamped into a pad on the left side
of the transmission, above the oil pan rail.

TRANSMISSION GEAR RATIOS

The gear ratios for the NAG1 automatic transmis-

sion are as follows:

1st Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.59:1
2nd Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.19:1
3rd Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.41:1
4th Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00:1
5th Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.83:1
Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.16:1

TRANSMISSION HOUSING

The converter housing and transmission are made

from a light alloy. These are bolted together and cen-
tered via the outer multi-disc carrier of multi-disc
holding clutch, B1. A coated intermediate plate pro-
vides the sealing. The oil pump and the outer multi-
disc carrier of the multi-disc holding clutch, B1, are
bolted to the converter housing. The stator shaft is
pressed into it and prevented from rotating by
splines. The electrohydraulic unit is bolted to the
transmission housing from underneath. A sheet
metal steel oil pan forms the closure.

MECHANICAL SECTION

The mechanical section consists of a input shaft,

output shaft, a sun gear shaft, and three planetary
gear sets which are coupled to each other. The plan-
etary gear sets each have four planetary pinion
gears. The oil pressure for the torque converter
lock-up clutch and clutch K2 is supplied through
bores in the input shaft. The oil pressure to clutch
K3 is transmitted through the output shaft. The
lubricating oil is distributed through additional bores
in both shafts. All the bearing points of the gear sets,
as well as the freewheeling clutches and actuators,
are supplied with lubricating oil. The parking lock
gear is connected to the output shaft via splines.

Freewheeling clutches F1 and F2 are used to opti-

mize the shifts. The front freewheel, F1, is supported
on the extension of the stator shaft on the transmis-
sion side and, in the locking direction, connects the
sun gear of the front planetary gear set to the trans-
mission housing. In the locking direction, the rear
freewheeling clutch, F2, connects the sun gear of the
center planetary gear set to the sun gear of the rear
planetary gear set.

ELECTROHYDRAULIC CONTROL UNIT

The electrohydraulic control unit comprises the

shift plate made from light alloy for the hydraulic
control and an electrical control unit. The electrical
control unit comprises of a supporting body made of
plastic, into which the electrical components are
assembled. The supporting body is mounted on the
shift plate and screwed to it.

Strip conductors inserted into the supporting body

make the connection between the electrical compo-
nents and a plug connector. The connection to the
wiring harness on the vehicle and the transmission
control module (TCM) is produced via this 13-pin
plug connector with a bayonet lock.

SHIFT GROUPS

The hydraulic control components (including actua-

tors) which are responsible for the pressure distribu-
tion before, during, and after a gear change are
described as a shift group. Each shift group contains
a command valve, a holding pressure shift valve, a
shift pressure shift valve, overlap regulating valve,
and a solenoid.

The hydraulic system contains three shift groups:

1-2/4-5, 2-3, and 3-4. Each shift group can also be
described as being in one of two possible states. The
active shift group is described as being in the shift
phase when it is actively engaging/disengaging a
clutch combination. The 1-2/4-5 shift group control
the B1 and K1 clutches. The 2-3 shift group controls
the K2 and K3 clutches. The 3-4 shift group controls
the K3 and B2 clutches.

OPERATION

The transmission control is divided into the elec-

tronic and hydraulic transmission control functions.
While the electronic transmission control is responsi-
ble for gear selection and for matching the pressures
to the torque to be transmitted, the transmission’s
power supply control occurs via hydraulic elements
in the electrohydraulic control module. The oil supply
to the hydraulic elements, such as the hydrodynamic
torque converter, the shift elements and the hydrau-
lic transmission control, is provided by way of an oil
pump connected with the torque converter.

The Transmission Control Module (TCM) allows for

the precise adaptation of pressures to the correspond-
ing operating conditions and to the engine output
during the gearshift phase, resulting in a noticeable
improvement in shift quality. The engine speed limit
can be reached in the individual gears at full throttle
and kickdown. The shift range can be changed in the
forward gears while driving, but the TCM employs a
downshift safeguard to prevent over-revving the
engine. The system offers the additional advantage of

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AUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATION

flexible adaptation to different vehicle and engine
variants.

EMERGENCY RUNNING FUNCTION

In order to ensure a safe driving state and to pre-

vent damage to the automatic transmission, the TCM
control module switches to limp-home mode in the
event of critical faults. A diagnostic trouble code
(DTC) assigned to the fault is stored in memory. All
solenoid and regulating valves are thus de-energized.

The net effect is:
• The last engaged gear remains engaged.
• The modulating pressure and shift pressures

rise to the maximum levels.

• The torque converter lockup clutch is deacti-

vated.

In order to preserve the operability of the vehicle

to some extent, the hydraulic control can be used to
engage 2nd gear or reverse using the following pro-
cedure:

• Stop the vehicle.
• Move selector lever to “P”.
• Switch off engine.
• Wait at least 10 seconds.
• Start engine.
• Move selector lever to D: 2nd gear.
• Move selector lever to R: Reverse gear.
The limp-home function remains active until the

DTC is rectified or the stored DTC is erased with the
appropriate scan tool. Sporadic faults can be reset
via ignition OFF/ON.

CLUTCH APPLICATION

Refer to CLUTCH APPLICATION for which shift

elements are applied in each gear position.

CLUTCH APPLICATION

GEAR

RATIO

3.59

2.19

1.41

1.00

0.83

N/A

3.16

R - Limp

1.93

* = The shift components required during coast.

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