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Section F
Transmission
17 - 4
Basic Operation
Powershift Gearbox
Hydraulic and Electrical Operation
Oil pump J is directly driven by the engine via the torque
converter.
Oil from the pump J is fed through an internal passage via
the filter Q to the pressure maintenance valve H, which
maintains pressure to the solenoid valve block for clutch
selection. Excess oil from the maintainance valve flows
b ac k t hrough t he c asing t o t he t orq ue c onvert er A.
Pressure in the converter is controlled by a relief valve G
which dumps oil from the converter line back to the sump.
Oil from the torque converter A flows out of the gearbox at
position M to the external oil cooler 6, returning to the
solenoid valve manifold block 5 at position N. The oil then
flows through internal oilways providing lubrication for
clutches and bearings before returning to the gearbox
sump.
The torque converter A is a fluid coupling bolted to a drive
plate which in turn is bolted to the engine flywheel. As the
engine starts to rotate, the converter gives smooth power
take off gradually increasing the torque transmitted. This
torque is transferred from the converter assembly to the
clutch/gear assemblies via input shaft on the forward
clutch assembly B.
Forward clutch assembly B contains two hydraulically
operated clutches; one clutch (T) provides a forward low
ratio drive and the other (U) a forward high ratio drive. Each
clutch is controlled by a 2-position solenoid valve. When
the applicable solenoid is energised, pressurised oil is
directed to either the forward low (solenoid Ts) or forward
high (solenoid Us) clutch.
The reverse clutch assembly C is similar to the forward
clutch assembly. It contains two hydraulically operated
clutches; one clutch (W) provides a reverse low ratio drive
and the other (V) a reverse high ratio drive. 2-position
solenoid valves when energised, direct pressurised oil to
either the reverse low (solenoid Ws), or reverse high
(solenoid Vs) clutch.
Both the mainshaft and the layshaft assemblies have a
single clutch each. Solenoid valve Zs, when energised,
directs pressurised oil to the layshaft clutch Z. Solenoid
valve Ys, when energised, directs pressurised oil to the
mainshaft clutch Y.
On 6 speed gearboxes, the 6 speed clutch X is controlled
via solenoid valve Xs.
Note: The 6 speed clutch assembly is so called as it is
fitted to 6 speed, and not 4 speed gearboxes. However,
the clutch is NOT engaged when 6th gear is selected. See
the adjacent table.
Note: All the clutches work on the same principle. For a full
description of operation see Systems Description.
9803/3280
www.WorkshopManuals.co.uk
The 2/4 wheel drive unit F also has a single clutch S. When
4WD is selected, pressurised oil is directed via solenoid
valve Ss to the 4WD clutch. When 2WD is selected a
connection from the clutch to the transmission sump is
made. For a full description of 2/4 wheel drive clutch
operation see Systems Description, 2/ 4WD Clutch
Operation
When a gear is selected via the control switch in the cab, 2
clutches are always engaged. By selecting different pairs of
clutches different gear ratios are engaged. On 4 speed
gearboxes the solenoids are electrically controlled using
relays. On 6 speed gearboxes the solenoids are controlled
by an electronic control unit (ECU) mounted in the cab.
Speed sensor 1 is used to enable the gear selection to be
managed automatically as required.
Example - 2nd gear forward 4WD (6 speed gearbox)
In the schematic, the gearbox is shown with 2nd gear
forward engaged. 2nd gear forward requires the forward
low clutch T and layshaft clutch Z to be engaged. When
the gear selection switch is moved to 2nd gear forward, the
electrical control system energises solenoid valves Ts and
Zs. Pressurised oil is diverted to the back of pistons in
both clutches to engage the drive. At the same time all
other solenoids are de-energised, diverting oil from the
back of the other clutch pistons to the gearbox sump. 4WD
clutch S is also energised to give 4 wheel drive.
The t ab les show w hic h c lut c hes and solenoid s are
engaged for each gear selection.
Note: Solenoid valve Xs controls clutch X, solenoid valve
Zs controls clutch Z and so on.
Purchased from www.WorkshopManuals.co.uk
4 Speed Powershift
Gear
Clutches engaged
Forward
Reverse
1st
T,Z
W,Z
2nd
U,Z
V,Z
3rd
T,Y
W,Y
4th
U,Y
V,Y
6 Speed Powershift
Gear
Clutches engaged
Forward
Reverse
1st
X,Z
W,Z
2nd
T,Z
V,Z
3rd
U,Z
W,Y
4th
X,Y
V,Y
5th
-
T,Y
6th
U,Y
-
Ts
Us
Ws
Vs
Ss
Ys
5
Zs
Xs
Section F
17 - 4
Key
A
Torque converter
B
Forward clutch assembly
C
Reverse clutch assembly
D
Mainshaft assembly
E
Layshaft assembly
F
2/4 wheel drive clutch assembly
G
Torque converter relief valve
H
Oil pressure maintenance valve
J
Transmission oil pump
K
6 speed assembly (if fitted)
L
4WD output yoke
M
Hose connection - to oil cooler
N
Hose connection - from oil cooler
P
Oil strainer
Q
Oil filter
R
Driveshaft (drives machine main hydraulic
pump)
S
2/4WD clutch
Ss 2/4WD clutch solenoid
T
Forward low ratio clutch
Ts Forward low ratio clutch solenoid
U
Forward high ratio clutch
Us Forward high ratio clutch solenoid
V
Reverse high ratio clutch
Vs Reverse high ratio clutch solenoid
W Reverse low ratio clutch
Ws Reverse low ratio clutch solenoid
X
6 speed clutch (6 speed gearbox only)
Xs 6 speed clutch solenoid (6 speed gearbox only)
Y
Mainshaft clutch
Ys Mainshaft clutch solenoid
Z
Layshaft clutch
Zs Layshaft clutch solenoid
1
Speed sensor
5
Solenoid valve manifold block
6
Gearbox oil cooler
Issue 1
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