wheel LAND ROVER DEFENDER 1999 Owner's Guide

26COOLING SYSTEM
10
DESCRIPTION AND OPERATION At low radiator temperatures, the fan operation is not required and the bi-metallic coil keeps the valve closed,
separating the silicone fluid from the drive plate. This allows the fan to’freewheel’reducing the load on the engine,
improving fuel consumption and reducing noise generated by the rotation of the fan.
When the radiator temperature increases, the bi-metallic coil reacts and moves the valve, allowing silicone fluid to
flow into the fluid chamber. The resistance to shear of the silicone fluid creates drag on the drive plate and
provides drive to the body and the fan blades.
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26COOLING SYSTEM
12
DESCRIPTION AND OPERATION Viscous Fan Operation
A = Cold
B = Hot
1.Drive plate
2.Fan body
3.Clearance
4.Valve plate
5.Valve
6.Bi-metallic coil7.Fluid seals
8.Ball race
9.Fluid chamber
10.Reservoir
11.Return port
When the engine is off and the fan is not rotating, the silicone fluid stabilises within the fluid chamber and the
reservoir. The fluid levels equalise due to the return port in the valve plate being open between the fluid chamber
and the reservoir. In this condition, when the engine is started, silicone fluid is present in the fluid chamber and
causes drag to occur between the drive plate and the body. This causes the fan to operate initially when the
engine is started.
As the fan speed increases, centrifugal force and a scoop formed on the fluid chamber side of the valve plate,
pushes the silicone fluid through the return port in the valve plate into the reservoir. As the fluid chamber empties,
the drag between the drive plate and the body is reduced, causing the drive plate to slip. This reduces the
rotational speed of the fan and allows it to’freewheel’.
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COOLING SYSTEM
13
DESCRIPTION AND OPERATION When the coolant temperature is low, the heat emitted from the radiator does not affect the bi-metallic coil. The
valve remains closed, preventing fluid escaping from the reservoir into the fluid chamber. In this condition the fan
will’freewheel’at a slow speed.
As the coolant temperature increases, the heat emitted from the radiator causes the bi-metallic coil to tighten. This
movement of the coil moves the valve to which it is attached. The rotation of the valve exposes ports in the valve
plate which allow the silicone fluid to spill into the fluid chamber. As the fluid flows into the clearance between the
annular grooves in the drive plate and body, drag is created between the two components. The drag is due to the
viscosity and shear qualities of the silicone fluid and causes the drive plate to rotate the body and fan blades.
As the coolant temperature decreases, the bi-metallic coil expands, rotating the valve and closing off the ports in
the valve plate. When the valve is closed, centrifugal force pushes the silicone fluid through the return port,
emptying the fluid chamber. As the fluid chamber empties, the drag between the drive plate and the body is
reduced and the body slips on the drive plate, slowing the rotational speed of the fan.
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CLUTCH
3
DESCRIPTION AND OPERATION 1.Brake/clutch reservoir
2.Connecting hose
3.Bolt - 2 off
4.Master cylinder
5.Clutch pedal
6.Gearbox housing
7.Primary driveshaft
8.Bolt - 2 off
9.Slave cylinder
10.Bleed nipple
11.Pressure plate
12.Drive plate
13.Dual mass flywheel
14.Metal hydraulic pipe
15.Ball spigot
16.Clutch release bearing sleeve
17.Bolt - 2 off
18.Pivot washer
19.Release lever
20.Release bearing
21.Retaining clip
22.Bolt
23.Plastic hydraulic pipe
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CLUTCH
5
DESCRIPTION AND OPERATION 1.Brake/clutch reservoir
2.Fluid supply pipe
3.Hydraulic feed pipe
4.Damper
5.Master cylinder
6.Piston
7.Clutch pedal
8.Primary driveshaft
9.Engine crankshaft
10.Drive plate
11.Dual mass flywheel
12.Ring gear
13.Leaf spring
14.Cover - pressure plate
15.Diaphragm
16.Release bearing
17.Ball spigot
18.Release bearing sleeve
19.Release lever
20.Slave cylinder
21.Piston
22.Bleed nipple
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33CLUTCH
6
DESCRIPTION AND OPERATION DESCRIPTION
General
The clutch system is a diaphragm type clutch operated by a hydraulic cylinder. The drive plate is of the rigid centre
type with no integral damping springs. The flywheel is of the dual mass type with damping springs integral with the
flywheel. The clutch requires no adjustment to compensate for wear.
Hydraulic Clutch
The hydraulic clutch comprises a master cylinder, slave cylinder and a hydraulic reservoir. The master and slave
cylinders are connected to each other hydraulically by plastic and metal pipes. The plastic section of the pipe
allows ease of pipe routing and also absorbs engine movements and vibrations.
The master cylinder comprises a body with a central bore. Two ports in the body connect the bore to the hydraulic
feed pipe to the slave cylinder and the fluid reservoir. The bore is also connected to a damper which prevents
engine pulses being transferred hydraulically to the clutch pedal. A piston is fitted in the bore and has an external
rod which is attached to the clutch pedal with a pin. Two coil springs on the clutch pedal reduce the effort required
to depress the pedal.
The master cylinder is mounted on the bulkhead and secured with two bolts. The cylinder is connected to the
shared brake/clutch reservoir on the brake servo by a braided connecting hose.
The slave cylinder is located on the left hand side of the gearbox housing and secured with two bolts. A heat
shield is fitted to protect the underside of the slave cylinder from heat generated from the exhaust system. The
slave cylinder comprises a cylinder with a piston and a rod. A port in the cylinder body provides the attachment for
the hydraulic feed pipe from the master cylinder. A second port is fitted witha bleed nipple used for removing air
from the hydraulic system after servicing. The piston rod locates on a clutch release lever located in the gearbox
housing. The rod is positively retained on the release lever with a clip.
Clutch Mechanism
The clutch mechanism comprises a flywheel, drive plate, pressure plate, release lever and a release bearing. The
clutch mechanism is fully enclosed at the rear of the engine by the gearbox housing.
A clutch release bearing sleeve is attached in the gearbox housing with two bolts and located on two dowels. A
spigot with a ball end is formed on the release bearing sleeve and provides a mounting and pivot point for the
clutch release lever. A dished pivot washer is located on the ball of the spigot. When the release lever is located
on the ball, the pivot washer seats against the rear face of the release lever. A spring clip is located on the lever
and the pivot washer and secures the lever on the spigot. A small bolt retains the spring clip in position.
The release lever is forked at its inner end and locates on the clutch release bearing carrier. The outer end of the
release lever has a nylon seat which locates the slave cylinder piston rod. A second nylon seat, positioned
centrally on the release lever, locates on the ball spigot of the release bearing sleeve and allows the release lever
to pivot freely around the ball.
The clutch release bearing locates on the clutch release lever and release bearing sleeve. The bearing is retained
on a carrier which has two flats to prevent the carrier rotating on the release lever. A clip retains the release lever
on the carrier. The bearing and carrier are not serviceable individually.
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CLUTCH
7
DESCRIPTION AND OPERATION Dual Mass Flywheel
1.Ring gear
2.Primary flywheel
3.Inner drive plate
4.Spring housing
5.Secondary flywheel
6.Rivet
7.Ball bearing8.Dowel location hole
9.Mounting hole
10.Inner spring
11.Outer spring
12.Crankshaft position sensing holes
13.Pressure plate locating dowel
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33CLUTCH
8
DESCRIPTION AND OPERATION The dual mass flywheel is bolted on the rear of the crankshaft with eight bolts. A dowel on the crankshaft flange
ensures that the flywheel is correctly located. A ring gear is fitted on the outer diameter of the flywheel. The ring
gear is not serviceable. Thirty blind holes are drilled in the outer diameter of the flywheel adjacent to the ring gear.
The holes are positioned at 10°intervals with four 20°spaces. The holes are used by the crankshaft position
sensor for engine management.
The dual mass flywheel is used to insulate the gearbox from torsional and transient vibrations produced by the
engine. The flywheel comprises primary and secondary flywheels with the drive between the two transferred by a
torsional damper which comprises four coil springs. The springs are located in the inside diameter of the primary
flywheel. Two of the springs are of smaller diameter and fit inside the larger diameter springs.
The primary flywheel locates the ring gear and is attached to the crankshaft flange with eight bolts. The two pairs
of coil springs are located in a recess in the flywheel between two riveted retainers. A roller bearing is pressed
onto the central boss of the primary flywheel and retained with a riveted plate. The bearing provides the mounting
for the secondary flywheel.
The secondary flywheel comprises two parts; an outer flywheel which provides the friction surface for the clutch
drive plate and an inner drive plate which transfers the drive from the primary flywheel, via the coil springs, to the
outer flywheel. The two components of the secondary flywheel are secured to each other with rivets. The inner
drive plate is located between the two pairs of coil springs and can rotate on the ball bearing in either direction
against the combined compression force of the four coil springs. Under high torque loading conditions the
secondary flywheel can rotate in either direction up to 70°in relation to the primary flywheel.
The operating face of the secondary flywheel is machined to provide a smooth surface for the drive plate to
engage on. Three dowels and six studs and nuts provide for the location and attachment of the pressure plate.
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33CLUTCH
10
DESCRIPTION AND OPERATION The pressure plate assembly comprises a pressure plate, cover and diaphragm and is mounted on and rotates
with the dual mass flywheel.
The pressure plate is forged from cast iron and machined to provide a smooth surface for the drive plate to
engage on. Three lugs on the outer diameter of the pressure plate connect it via three leaf spring to the cover. The
leaf springs have three tempered steel leaves which assist in pulling the pressure plate away from the drive plate
when the clutch pedal is depressed.
The cover is made from pressed steel and houses all pressure plate components. Shouldered rivets support the
diaphragm inside the cover. The rivets heads are chamfered to allow the diaphragm to pivot when pressure is
applied to it by the release bearing. Three holes in the cover locate on the dowels on the flywheel and six further
holes provide for the attachment of the cover to the flywheel with six nuts. Larger holes in the cover provide
ventilation for the drive plate and pressure plate and flywheel contact surfaces.
The diaphragm comprises a cast ring with eighteen fingers. The diaphragm is attached to the cover with nine
shouldered rivets. The inner head of each rivet is chamfered to allow the diaphragm to pivot when the clutch is
depressed or released. When pressure is applied to the fingers of the diaphragm by the release bearing, the
diaphragm pivots on the rivets and moves away from the pressure plate, releasing the force applied to the
pressure plate and allowing the drive plate to slip between the pressure plate and the flywheel.
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CLUTCH
11
DESCRIPTION AND OPERATION Drive plate
1.Friction material
2.Inner plate3.Hub
4.Spring steel plate
The drive plate is of the rigid centre type and is sandwiched between the flywheel and the pressure plate. The
drive plate has a splined hub which engages with the splines on the primary drive shaft from the gearbox. The hub
is attached to an inner plate which is pressed onto the hub. A spring steel plate is riveted to the inner plate with
eight rivets and provides the attachment surface for the drive plate friction material. The spring steel plate allows
some axial compliance and contributes to smooth clutch operation. The friction material comprises two 267 mm
(10.5 in.) discs which are secured with rivets to each side of the spring steel plate. The rivets are installed through
recessed holes in the disc and emerge in recessed holes in the opposite disc.
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