Clutch/brakes (CV-A, CV-B, CV-C, CV-D/BV-E,
BV-F and BV-G) (Fig. 5.39) The clutch valves
control the engagement and disengagement of the
multiplate clutches and brakes. These valves are
variable pressure reduction valves which are actu-
ated by the appropriate solenoid valves, electronic
pressure regulator valves, traction valves and shift
valves and are responsible for producing the
desired clutch pressure variations during each
gear shift phase. Clutch valves CV-B, CV-C and
CV-F are influenced by modulation pressure which
resists the partial closure of the clutch valves, hence
it permits relatively high fluid pressure to reach
these multiplate clutches and brake when large
transmission torque is being transmitted.
Retaining valves (RV-E and RV-G) (Fig. 5.39) In
addition to the electronic pressure regulator valve
which actuates the clutch valves, the retaining
valves RV-E and RV-G modify the opening and
closing phases of the clutch valves in such a way as
to cause a progressive build-up or a rapid collapse
of operating multiplate clutch/brake fluid pressure
during engagement or disengagement respectively.
Traction/coasting valve (T/C-V) (Fig. 5.39) The
traction coasting valve T/C-V cuts out the regulat-
ing action of the traction valve TV (5±4) and shifts
the traction valve TV (4±5) into the shut-off posi-
tion when required.
Traction valve (TV) (4±5) (Fig. 5.39) The traction
valve TV (4±5) controls the main system fluid pres-
sure to the multiplate-clutch MPC-B via the trac-

Converter lock-up clutch valve (CLCV)
(Fig. 5.39) The converter lock-up clutch valve
`CLCV' is actuated with the converter pressure
control valve `CPCV' by the electronic pressure
regulation valve `EPRV-4'. The converter lock-up
clutch valve `CLCV' when actuated changes the
direction of input flow at reduced system pressure
from the drive-plate to the turbine wheel side of the
lock-up clutch. Simultaneously the converter pres-
sure valve `CPV' is actuated, this shifts the valve so
that the space between the drive-plate and lock-up
clutch face is vented. As a result the lock-up clutch
is forced hard against the drive-plate thus locking
out the torque converter function and replacing
it with direct mechanical drive via the lock-up
clutch.
Lubrication pressure valve (LPV) (Fig. 5.39) The
lubrication pressure valve `LPV' supplies fluid
lubricant at a suitable reduced system pressure to
the internal rubbing parts of the transmission gear
train.
5.10.8 Operating description of the electro/
hydraulic control unit
To simplify the various solenoid valve, clutch and
brake engagement sequences for each gear ratio
Table 5.6 has been included.
Neutral and park position (Fig. 5.39) With the
selector lever in neutral or park position, fluid is
delivered from the oil-pump to the selector position
valve `SPV', modulation pressure valve `MOD-V',

valve `SPV' then passes via the traction valves `TV
(4±5) and TV (5±4)' respectively to clutch valve
`CV-B', it therefore permits fluid pressure to
apply the multiplate clutch `MPC-B'.
2 Energizing solenoid valves `MV1 and MV2' opens
both valves. Solenoid valve `MV1' applies a
reduced constant fluid pressure to the left-hand
side of shift valves `SV-1 and SV-3'. Shift valve
`SV-1' shifts over to the right-hand side against
the tension of the return spring blocking the fluid
pressure passage leading to clutch valve `CV-D',
however shift valve `SV-3' cannot move over
since a similar reduced constant pressure is intro-
duced to the spring end of the valve via solenoid
valve `MV2'. Solenoid valve `MV2' applies
reduced constant pressure to the left-hand side
of shift valve `SV-2' and the right-hand side of
shift valve `SV-3'; this pushes the shift valve
`SV-2' to the right and so prevents shift valve
`SV-3' also being pushed to the right by fluid
pressure from solenoid valve `MV1' as pre-
viously mentioned.
3 Electronic pressure regulator valve `EPRV-1'
supplies a variable regulated fluid pressure to
the modulation pressure valve `MOD-PV', this
pressure being continuously adjusted by the elec-
tronic transmission control unit `ETCU' to suit
the operating conditions. Electronic pressure
regulating valve `EPRV-3 supplies a variable
controlling fluid pressure to brake and retaining

`MPB-G'.
4 The electronic pressure regulating valve `EPRV-2'
has its controlling current reduced, thus pro-
gressively closing the valve, consequently there
will be an increase in fluid pressure acting on the
right-hand side of both brake and retaining
valves `BV-E and RV-E' respectively. As a result
the brake valve `BV-E' opens to permit line pres-
sure to actuate and apply the multiplate brake
`MPB-E'.
Third gear (Fig. 5.43) Engagement of third gear is
obtained by applying the multiplate clutches
`MPC-B and MPC-D' and the multiplate brake
MPB-E.
The shift from second to third gear is achieved in
the following manner with the selector position
valve in the D drive range:
1 Multiplate clutch `MPC-B' and multiplate brake
`MPB-E' are applied as for second gear.
2 Solenoid valve `MV2' remains energized thus
keeping the valve open as for first and second
gear.
173
CLC
TTCP
S
OWC
MPB
E
MPC

FIQ
(torque)
TVP
(acceleration)
SS
engine/trans.
Transmission
program
ETCU
GCPS
1 2 3 DNRP
MV3
MV1
MV2
PRV-1
SV-1
SV-2
SV-3
1
MPV
BV-F
SPV
P
EPRV-1
TV (4-5)
MOD-PV
PRV-2
EPRV-2
EPRV-3
EPRV-4

(T/C)V
CPV
CLCV
CPCV
LPV
CV-B
TV (5-4)
MPC
D
NRV
to
LUB
176
FIQ
(torque)
TVP
(acceleration)
SS
engine/trans.
Transmission
program
ETCU
1 2 3 DNRP
GCPS
Y
P
SPV
2
MPV
BV-F

F
MPB
G
MPC
D
RV-E
RV-G
BV-E
BV-G
RGV
BV-D
CV-B
CV-C
Y
(T/C)V
TV (5-4)
CPV
CLCV
CPCV
to
LUB
LPV
PRV
NRV
178
FIQ
(torque)
TVP
(acceleration)
SS

179
CLC
TTCP
S
OWC
MPB
E
MPC
A
MPC
B
MPC
C
MPB
F
MPB
G
MPC
D
RV-E
RV-G
BV-E
BV-G
RGV
BV-D
CV-B
CV-C
(T/C)V
TV (5-4)
CPV

BV-F
SPV
P
EPRV-1
TV (4-5)
MOD-PV
PRV-2
EPRV-2
EPRV-3
EPRV-4
Y
4
Fig. 5.44 Hydraulic/electronic transmission control system ± fourth gear
181
CLC
TTCP
S
OWC
MPB
E
MPC
A
MPC
B
MPC
C
MPB
F
MPB
G

ETCU
GCPS
1 2 3 DNRP
MV3
MV1
MV2
PRV-1
SV-1
SV-2
SV-3
5
MPV
BV-F
SPV
P
EPRV-1
TV (4-5)
MOD-PV
PRV-2
EPRV-2
EPRV-3
EPRV-4
Y
PRV
NRV
Fig. 5.45 Hydraulic/electronic transmission control system ± fifth gear
183
CLC
TTCP
S

Lub
LPV
PRV
NRV
184
FIQ
(torque)
TVP
(acceleration)
SS
engine/trans.
Transmission
program
ETCU
GCPS
1 2 3 DNRP
MV3
MV1
MV2
PRV-1
SV-1
SV-2
SV-3
R
MPV
BV-F
SPV
P
EPRV-1
TV (4-5)

hand side. Subsequently line pressure now passes
via the shift valve `SV-1' to the clutch valve `CV-D'
and hence applies the multiplate clutch `MPC-D'.
Fourth gear (Fig. 5.44) Engagement of fourth
gear is obtained by applying the multiplate clutches
`MPC-B, MPC-C and MPC-D'.
The shift from third to fourth gear is achieved in
the following manner with the selector position
valve in the D drive range:
1 Multiplate clutches `MPC-B and MPC-D'
applied as for third gear.
2 Solenoid valves `MV1 and MV3' de-energized
and closed as for third gear.
3 Electronic pressure regulating valve `EPRV-1'
de-energized and partially closed, whereas
`EPRV-3' remains energized and open, both
valves operating as for third gear.
4 Electronic pressure regulating valve `EPRV-2'
now progressively energizes and opens, this
removes the control pressure from brake and
retaining valves `BV-E and RV-E' respectively.
Line pressure to brake valve `BV-E' is now
blocked causing the release (exhausting) of fluid
pressure via the brake valve `BV-E' and the dis-
engagement of the multiplate brake `MPB-E'.
5 Fluid pressure now passes though to the multi-
plate clutch `MPC-C' via shift valves `SV-1 and
SV-2', and clutch-valve `CV-C'. Subsequently,
the multiplate clutch `MPC-C' is applied to
complete the gear shift from third to fourth gear.

gear.
3 Solenoid valve `MV3' is energized, this allows
fluid pressure via passage `Y-Y' to shift trac-
tion/coasting valve `(T/C)V' over to the right-
hand side. As a result fluid pressure is released
(exhausts) from the spring side of the traction
valve `TV (5±4)', hence fluid pressure acting on
the left-hand end of the valve now enables it to
shift to the right-hand side.
4 Solenoid valve `MV1' is energized, this pres-
surizes the left-hand side of the shift valves `SV-1
and SV-3'. However, `SV-1' cannot move over
due to the existing fluid pressure acting on the
spring end of the valve, whereas `SV-3' is free to
shift to the right-hand end. Fluid pressure from
the clutch valve `CV-E' now passes via shift valve
`SV-3' and traction/coasting valve `(T/C)V' to
the traction valve `TV (4±5)' causing the latter
to shift to the right-hand side. Consequently
traction valve `TV (4±5)' now blocks the main
fluid pressure passing through the clutch valve
`CV-B' and simultaneously releases the multi-
plate clutch `MPC-B' by exhausting the fluid
pressure being applied to it.
5 Electronic pressure regulating valve `EPRV-2'
de-energized and partially closed. Controlled
186
fluid pressure now passes to the right-hand end
of the clutch valve `CV-E' and retaining valve
`RV-E', thus causing both valves to shift to the

5 Selector position valve `SPV' in reverse position
diverts fluid pressure from the fluid pump,
directly to multiplate clutch `MPC-A' and
indirectly to multiplate brake `MPB-F' via the
selector position valve `SPV', reverse gear
valve `RGV', shift valve `SV-2' and the clutch
valve `CV-F'. Both multiplate clutch `MPC-A'
and multiplate brake `MPB-F' are therefore
applied.
5.11 Semi-automatic (manual gear change two
pedal control) transmission system
5.11.1 Description of transmission system
(Fig. 5.48)
The system being described is broadly based on the
ZF Man Tip Matic/ZF AS Tronic 12 speed twin
countershaft three speed constant mesh gearbox
with a front mounted two speed `splitter' gear
change and a rear positioned single stage two
speed epicyclic gear `range' change; however, the
basic concept has been modified and considerably
simplified in this text.
Gear changes are achieved by four pneumati-
cally operated power cylinders and pistons which
are attached to the ends of the three selector rods,
there being one power cylinder and piston for each
of the splitter and range selector rods and two for
the three speed and reverse constant mesh two
piece selector rod. Gear shifts are actuated by
inlet and exhaust solenoid control valves which
supply and release air to the various shift power

prevailing engine torque and road resistance con-
ditions are matched.
5.11.2 Splitter gear change stage (Fig. 5.47)
Power flows via the clutch and input shaft to the
splitter synchromesh dog clutch. The splitter syn-
chromesh dog clutch can engage either the left or
right hand matching dog clutch teeth on the central
splitter gear mounted on the input shaft to obtain a
low splitter gear ratio, or to the central third gear
187
R
L
H
L
H
L
H
L
H
L
H
L
H
Input
Power flow path
Output
R
1
2
3

P
S
C
P
C
A
H
Power
piston
Splitter
Gearbox
Range shift
power cylinder
Constant
mesh
power cylinder
Selector rod
plunger & spring
Constant mesh
three speed and
reverse gear box
3
2
1
Epicyclic
single stage
gearing
range gear box
L
H

2
3
4
5
6
Fig. 5.47 Twin countershaft 12 speed constant mesh gearbox with synchromesh two speed splitter and range changes
188
mounted on the mainshaft to obtain the high split-
ter gear ratio. Power is now able to pass via the
twin countershafts to each of the mainshaft con-
stant mesh central gears by way of the constant
mesh gears 1, 2, 3 and R.
5.11.3 Constant mesh 1-2-3 and R gear stage
(Fig. 5.47)
The selection and engagement of one of the sliding
dog clutch set of teeth either with R, 1, 2 or 3
floating mainshaft central constant mesh gears per-
mits the drive path to flow from the twin counter-
shaft gears via the mainshaft to the epicylic range
change single stage gear train.
5.11.4 Range change gear stage (Fig. 5.47)
Low range gear selection With the synchromesh
dog clutch hub moved to the left-hand side, the
internal toothed annular gear (A) will be held sta-
tionary; the drive from floating mainshaft is there-
fore compelled to pass from the central sun gear (S)
to the output shaft via the planet gear carrier (C
P
)
(see Fig. 5.47). Now since the annular gear is held

sion drive are vehicle load, which includes pull-
ing away from a standstill and any road gradient,
vehicle speed and engine speed. Thus the vehicle's
resistance to move is monitored in terms of engine
load by the electronic diesel control unit `EDCU'
which is part of the diesel engine's fuel injection
equipment, and engine speed is also monitored by
the EDCU, whereas vehicle speed or wheel speed is
monitored by the wheel brake speed sensors. These
three factors are continuously being monitored, the
information is then passed on to the electronic
transmission control unit `ETCU' which processes
it so that commands can be transferred in the form
of electric current to the inlet and exhaust clutch
actuator solenoid control valves.
Engagement and disengagement of clutch when
pulling away from a standstill (Fig. 5.48) With
the vehicle stationary, the ignition switched on
and first gear selected, the informed ETCU ener-
gizes and opens the clutch solenoid inlet control
valve whereas the exhaust control valve remains
closed (see Fig. 5.48). Compressed air now enters
the clutch cylinder actuator, this pushes the piston
and rod outwards causing the clutch lever to pivot
and to pull back the clutch release bearing and
sleeve. As a result the clutch drive disc plate and
input shaft to the gearbox will be disengaged from
the engine. As the driver depresses the accelerator
pedal the engine speed commences to increase
(monitored by the engine speed sensor), the

solenoid control valves
Selector
rod
plunger
and
spring
Low gear
range
engaged
Selector
fork
Constant mesh 1-R shift
solenoid control valves
L
H
1-R shift
power cylinder
Exhaust
valve
1-R
selector
fork
1C
RC
Inlet
valve
Range
fork
1
R

Splitter shift
solenoid control
valves
3–2
selector
fork
Splitter
fork
L
H
Low gear
splitter
engaged
Splitter
selector
rod
Inlet valve
Transmission
multiplate
brake
HR
LR
2C
EVC
EVC
IVO
IVO
3C
IVC
IVC

diesel
control
unit
Gear
selector
switch
control
stick
Clutch
actuator
solenoid
control
valves
Inlet valve
Exhaust valve
Clutch actuator cylinder
3
2
Single
plate dry
clutch
Clutch
disengaged
Splitter shift
power cylinder
Fig. 5.48 A simplified electro/pneumatic gear shift and clutch control
190
with the vehicle moving forwards, the ETCU
immediately signals the clutch solenoid control
valves to operate so that the compressed air can

their speed with that of the mainshaft, then at this
point the appropriate constant mesh dog clutch can
easily slide into mesh with it adjacent central gear
dog teeth. Immediately after the gear shift the
transmission brake inlet valve closes and the
exhaust valve opens to release the compressed air
from the multiplate clutch cylinder thereby pre-
venting excessive binding and strain imposed to
the friction plates and assembly.
5.11.7 Splitter gear shifts (Fig. 5.48)
The splitter gear shift between low and high gear
ratio takes place though a synchromesh type dog
clutch device. Note for all the gear changes taking
place in the gearbox, the splitter gears are con-
stantly shifted from low to high going up the gear
ratios or from high to low going down the gear
ratios. With ignition switched on and the gear
selector stick positioned say in low gear, the
ETCU signals the splitter solenoid control to
close and open the inlet and exhaust valves respec-
tively for the high splitter gear solenoid control,
and at the same time to close and open the exhaust
and inlet valves respectively for the low splitter gear
solenoid control (see Fig. 5.48). The splitter shift
power cylinder will now operate, compressed air
will be released from the left-hand side and
simultaneously compressed air will be intro-
duced to the right-hand side of the splitter
shift power cylinder; the piston and selector
rod now smoothly shift to the low splitter gear

needed for the low range shift.
5.11.9 Constant mesh three speed and reverse
gear shift (Figs 5.47 and 5.48)
These gear shifts cover the middle section of the
gearbox which involves the engagement and disen-
gagement of the various central mainshaft constant
mesh gears via a pair of sliding dog clutches. There
is a dog clutch for engagement and disengagement
for gears 1-R and similarly a second dog clutch for
gears 2±3.
191